This is the first in a series. Special to Leeham News.
By Peter W. Lemme
Feb. 2, 2021, © Leeham News: The Boeing 707 entered service in 1958. 60 years later, a Boeing 737 MAX, the model’s fourth generation, crashed into the sea with all lives tragically lost. After, the 737 entered service in 1968, every subsequent 737 model was carefully crafted with the minimum changes necessary to deliver performance and reliability improvements. Differences were discouraged in order to reduce pilot training requirements, holding dear to visible family traits pioneered by the 707.
Changes that jeopardized an amended Federal Aviation Administration Type Certificate were culled. A new type certificate is a costly and lengthy process, with considerable risk.
The 757 should have saved Boeing from endless 737 generations, but the will of the customer changed its trajectory from the start, in the end leaving no mark at all.
The 737-100 was a marvel by fitting the engine tight under the wing, and every generation since has marveled at how to fit the latest engine under the wing.
Every swept wing air transport suffers growing pains, working out issues with flying qualities.
The 737 seems to have diverged from the other Boeing airplanes progressively. Should the 737 MAX’s now-infamous Maneuvering Augmentation Characteristics System (MCAS) implementation have been applied to the stabilizer? Did Boeing have a better choice?
Flying qualities approved “to the letter”, quantitatively, are balanced by qualitative measures, with latitude in judging acceptable performance.
The 737 family was fundamentally refreshed three times: Classic, NG, and MAX. In each case, customers with earlier 737 models expected that the newest model would require minimal differences training. Airlines prefer to minimize training, especially full-flight regime simulator time, to reduce cost and to speed up the approvals.
FAA criteria (AC 120-53B) defines a process for addressing differences between aircraft models for pilot qualification required for flying different variants of transport aircraft with the same type certificate (TC) and between aircraft with different TCs, that have been “designated” by the Administrator as related (Common).
To address aircraft differences pertinent to pilots safely flying those assigned aircraft, the FAA’s Flight Standardization Board (FSB) issues a report to specify the basis for the approval of airline programs for pilot qualification, as necessary for the operation of any airline aircraft under 14 CFR Parts 61, 91, 121. Airline pilot qualification to fly these aircraft types and variants with differences include necessary provisions for training, checking, and recency.
The FAA FSB Report for the B737 addresses the specifics needed for each variant of B737 flown. These are included in the FAA FSB Report for the B737, in the criteria listed as the “Master Difference Requirements” (MDR) Tables.
Master Difference Requirements are applied to each specific airline flying B737s, tailored for their particular set of B737 models or variants flown, in their airline specific “Operator Difference Requirements (ODR) tables”. Each airline’s pilot qualification program is designed to fully address any specific training, checking, or recency requirements needed, to fly each B737 variant applicable to that airline.
US regulatory requirements for the pilot in command of a jet transport aircraft flown in airline service specify that the pilot in command must both hold a suitable type-rating for that type aircraft flown, and also have completed any required qualification under FAR 121 as needed, before that pilot can operate that airplane in airline service. This typically involves training, checking, and recency of experience, but can also involve various aspects such as supervised flying with a Check Airman termed “Initial Operating Experience” (more recently just termed “Operating Experience”). Other aspects of qualification include Route Qualification, International Qualification, special Airport Qualification, and potentially other provisions.
In some instances, a pilot serving as a “Second-In-Command” pilot may also need to be “type rated”, to meet ICAO requirement as well as meeting additional qualifications.
One of the key elements of Initial or Upgrade Pilot training is “Differences” training applicable to flying different models or variants of a model. As an example, consider the B757 and B767. Originally, a pilot could be type-rated in the Boeing 757, or the Boeing 767, or both. Later (in 1983) FAA made a determination that a Pilot holding either a B757 Pilot Type Rating, or a B767 Pilot Type rating would be considered to have both type ratings (designated as a “B757 B767 Common Type Rating”) listed on that pilot’s Airman Certificate. However, to fly either type in airline service, suitable differences training still would be needed in each specific model actually flown. While both the Boeing 757 and 767 may in general be flown by a pilot with a “Boeing 757 767” Common Type Rating, all the other FAR 121 specific qualification requirements, such as “Differences” training, must still be met.
For the Boeing 737 series, one pilot Type Rating currently is assigned by the FAA (B737), and that Type Rating on the Airman Certificate covers flying any Boeing 737. However, in airline service, a B737 pilot still must also meet all the necessary qualification provisions for each specific model (variant) of the B737 flown.
Both a 737 PIC and SIC must satisfy any necessary difference training, checking, and recency requirements, as specified by the FAA’s Flight Standardization Board (FAA FSB), to operate each different Boeing 737 model (variant).
A new type certificate (14 CFR Part 25) application sets the regulatory basis in effect at the time of application, as the certification basis for the type. Whereas an amended type certificate may or may not necessarily have to re-establish parts or much of the certification basis, at the time an amended Type Certificate is initially sought. An amended type certificate can prolong applicability of criteria otherwise no longer used, based on acceptable safe in-service history of the basic type to be modified.
Usually, some elements of an updated regulatory basis are agreed upon, with some subsequent regulatory provisions not required. In other instances, an applicant may be encouraged to voluntarily apply an updated provision, or an equivalent provision.
Boeing applied for an amended type certificate with each new 737 model. Significant regulatory basis changes were also agreed between FAA and Boeing, and subsequently made, for each successive B737 derivative generation.
The Boeing 737 was the most advanced airplane Boeing had built. Pushing the envelope for their first two-crew flight deck meant more automation, reliability and simplicity. The issue was not simply putting all the flight engineer instruments and controls in front of the pilots. The Boeing 737 was the first airplane certificated in production with Category II automatic approach capability.
Figure 2: 737-200 Advanced Flight Deck. Source: Wikimedia Commons
Southwest Airlines led the way on the 737, yet held it back at the same time, for the Classic, the NG and for the MAX. Is there such a thing as too much LUV? Is the most successful airplane Boeing ever built handicapped by the dynamic that makes it so attractive?
T.M. Sell, Valley Daily News, 17 June 1993: For Boeing worker, 737 is No. 1
In early 1981, then Renton Division chief Frank Shrontz (Boeing Chairman in 1993) pursued the idea of an upgraded 737. Boeing’s own marketing experts predicted only 140 sales of the new version. Ron Woodard (Boeing Commercial EVP) said Shrontz had to talk them into raising the estimate to 180 to convince Boeing’s board to launch the new version.
By 1993, customers had ordered 3,100 737s.
“No one has ever built so many commercial airplanes of any one type,” Woodard said, “In fact, no one has come close.”
Sales for the 737-300 did not budge the year after it was launched, while the Original models continued unabated, reaching the 1,000-airplane milestone.
Figure 3: Chuck Yeager with Herb Kelleher. Source: Southwest Community Forum
In Southwest’s own recount, the airline takes credit for the 737 “classic.”
Southwest Community Forum: If not for Southwest, the 737 might have stopped with the -200 Advanced
Deregulation in 1978 allowed Southwest to expand beyond the borders of Texas, but it needed an aircraft that would allow it to compete on longer routes from San Antonio and Houston to the West Coast.
The larger 737-300, with its more powerful engines, greater range, and greater performance was the perfect airplane.
Southwest and US Airways were the launch Customers.
Ironically, none of the other airlines showed initial interest as they were happy with the 737-200 for shorter flights and had 727s serving the same markets that would be flown by the 737-300.
Without the launch customers’ support, the 737 line might well have ended with the -200.
The brand new 737-300 made its worldwide airline debut on December 17, 1984. Because this was the anniversary of the Wright Brothers first flight, the aircraft, N300SW, was named The Spirit of Kitty Hawk. The Spirit of Kitty Hawk is on permanent display at the Frontiers of Flight museum in Dallas.
The funny thing about calling a product “next generation” is that the name makes no sense once the product is in service plus it boxes you in for naming the inevitable “next” product afterwards.
The 737 Next Generation, or NG, represented almost a whole new airplane. It was all about performance, cost, commonality. Nothing more.
T.M. Sell, Valley Daily News, 17 June 1993: 737 on a Roll
Ron Woodard, EVP Boeing Commercial, and Gordon Bethune, vice president and general manager of the Renton Division, said Boeing is pursuing development of the 737-X, a jet that will have greater wing-span and improved engines to provide greater performance at lower cost.
He said the new jet will include only improvements that customers definitely want. “One very important thing we’ve learned is you don’t mess with success,” said Woodard.
“Simplicity, reliability and family commonality,” Woodard said. “That’s what our customers are telling us.”
“One airline executive has said ‘Stop right there. Put a lock on the cockpit.’” Bethune said. “They’re not interested in technology for technology’s sake.”
On Dec. 17, 1997, Southwest became the first operator of the 737 NG.
Boeing Mediaroom: First Boeing 737-700 Goes to Southwest Airlines
“Boeing has been fortunate to have Southwest as a successful business partner over the past 26 years, and we wish them continued success with their Next-Generation 737s,” said Ron Woodard, president of Boeing Commercial Airplanes. Southwest’s fleet of 258 jetliners consists entirely of Boeing 737s.
Modifications to the Next-Generation 737’s wing and engine provide improved fuel capacity, fuel efficiency, speed and range. The total wing area increased by 25 percent to 1,340 square feet (125 square meters), providing 30 percent more fuel capacity for a total of 6,878 U.S. gallons (26,136 liters).
The airplane’s range is approximately 3,200 nautical miles (3,682 statute miles or 5,926 kilometers), an increase of up to 900 nautical miles over current production 737s. This will allow U.S. transcontinental flights and increased 737 route capability throughout the world.
The 737-700 is powered by new CFM56-7 engines produced by CFMI, a joint venture of General Electric of the United States and Snecma of France. The CFM56-7 will have a 10-percent higher thrust capability than the CFM56-3C engines that power today’s 737s.
Commonality does not advance like engines, wings, and materials.
Boeing pilot Ray Craig promoted commonality.
Dan Dornseif: Boeing 737, The World’s Jetliner
Ray Craig said, “The goal from the Classic to the NG was one day of differences training for pilots, with no simulator required. We were striving to keep, as much as we could, similar handling qualities and minimize the training differences for the airlines.”
Aside from the addition of EFIS flight instrumentation to the flight deck (which could be configured with software to be visually similar to the Classics), most of the other changes made to the 737NG series were not any major consequence to the flight crew.
Flightblogger, Feb. 10, 2011
Boeing boss green-lights all-new next generation narrowbody
Speaking at the Cowen and Company Aerospace and Defense Conference in New York City, McNerney says: “We’re gonna do a new airplane. We’re not done evaluating this whole situation yet, but our current bias is to not re-engine, is to move to an all-new airplane at the end of the decade, or the beginning of the next decade.”
McNerney suggests that the A320neo has put pressure on the smaller Bombardier C-Series, which shares a common power plant in the Pratt & Whitney PW1000G geared turbofan platform. While Airbus has focused on its existing customer base McNerney sees a looming threat to the 737: “That doesn’t mean that as [Airbus gets] deeper in the development they’re not going to approach our customer base. I think they will.”
McNerney adds: “It’s our judgment that our customers will wait for us, rather than move to an airplane that will obsolete itself when [Airbus develops] a new airplane. I understand why they’re doing [the neo], we haven’t seen the need for it yet. I feel pretty comfortable we can defend our customer base, both because they’re not going ahead of us, they’re catching up to us, and because we’re going to be doing a new airplane that will go beyond the capability of what the neo can do.”
Boeing had struggled with downsizing the 787 in Project Yellowstone, or Y-1. In the end, the flight instruments were the biggest contribution, yet without managed crew alerting.
David Parker Brown, AirlineReporter, 16 Feb 2011: Could this be what the next Boeing 737 will look like?
At a recent Boeing media event Scott Fancher, the Vice President and General Manager of the 787 Dreamliner Program was asked what new technologies from the 787 could be scaled down for the new Boeing 737. When asked about composite materials being found in the new 737, he stated, “some composites scale down nicely, but others, they don’t.” He explained that some of the new systems technology and engine efficiencies could also be scaled down. Boeing feels that all the investments made on the 787 Dreamliner will serve as a basis for future new aircraft.
Southwest was the launch customer for the 737-300 Classic and, in November 1993, for the 737 NG. This history and the growing size over the decades of Southwest’s orders for 737s, became a crucial factor in the development of the MAX.
Scott Hamilton, Leeham News, “When the MAX was launched in July 2011 by American Airlines, Southwest’s CEO Gary Kelly was reportedly miffed. Southwest had urged Boeing to launch a re-engined 737, but the company dithered between this and an entirely new design. Airbus forced Boeing’s hand with a huge order from American for the A320 family. Backed into a corner, Boeing launched what became the MAX.”
Kelly tried to take the sting out of American’s being the first customer for the new 737 model.
Seattle Times: Southwest is launch customer for Boeing 737 MAX but won’t get the first delivery
There’s more to being a launch customer than bragging rights — although that’s a large part of the appeal of being the first to market with a shiny new jet. Aircraft makers also promise that their newest models boast lower fuel and maintenance costs than prior airplanes, providing an immediate bottom-line boost to airlines.
“We’re the launch customer, regardless of when we take the first delivery,” Southwest CEO Gary Kelly said of the MAX.
His chief operating officer, Mike Van De Ven, said Thursday that “we’re the ones that have done the service-ready operational validation for Boeing. We’re the ones working very closely with Boeing to make sure it’s operating as everyone intended.”
Boeing’s MAX development is on-budget and ahead of schedule. All this good news, as far as production is concerned, is a rarity in an industry renowned for being late to everything.
In the end, the MAX ran significantly over budget. And schedule and budget would haunt Boeing in the aftermath of two fatal accidents.
The first Boeing 737 was the last new airplane to be built at Plant 2 on Boeing Field in Seattle, with a production run that included the legendary B-17 Flying Fortress, B-52 Stratofortress and the world’s first large swept-wing jet — the XB-47 Stratojet.
The 737 evolution was stalled by commonality. Airlines want to minimize differences to make it easy for pilots to transition between the various models. Once cast, the 737 was forever anchored in the past.
Airbus A320 entered the market in 1989 with full-flight regime fly-by-wire. The choice of non-moving throttles and uncoupled sidesticks was a significant departure from any other air transport. Boeing remained faithful to the control column and moving throttles with the 777 and 787 entrants. The Airbus A220 stands in contrast to the rest of the Airbus fleet, with moving throttles and uncoupled side sticks. Airbus has replicated the A320 flight deck design to the A330, A340, A380, and their latest A350. Gulfstream G500/G600/G650 have moving throttles and coupled sidesticks or active sidesticks.
While most examples of commonality hold an airplane back, the 747-400 was pushed ahead, instead.
Philip Bartles, Boeing 747-400
Boeing consulted 14 major international airlines. Boeing wanted to go for a minimum-change aircraft, particularly on the flight deck, where the analog instruments were to be retained. This was supported by Cathay, one of the launch customers, in order to minimize training.
However, there was strong pressure from the other potential launch customers to update the flight deck, since they were experiencing the advantages of the 757/767 entry into service and the advanced flight decks of the Airbus family.
Each generation of the 737 accommodated new engines, new displays, and new features. The 747, when faced with the same proposition, broke with the 747-400, an advancement from the 757/767. The 777 and 787 each followed from the 747-400. Yet the 757 influence is lost to the 737.
Figure 4: 737 development compared to its competitors. Source: Peter Lemme
Boeing never perceived that technology itself holds the 737 back, for it has been behind since 1989. This position was re-affirmed in the most recent two generations, the NG and MAX. Design changes focused on fuel savings, growth, common parts, and minimum difference training for the pilots.
Airline emphasis on commonality discourages change or favors older designs as a winning proposition.
The Boeing 757 set the stage for the Boeing 737 to persist for four generations. Had the 757 been built as planned, with a two-member 757-100/200 family (the -300 came much later) to fill the 150-160 seat capacity that the 727-200 pioneered, everything would have been different. The 737-500 would have been the last 737, there would have been no NG.
Peter Rinearson offers some very keen insights that relate well to the 737 story.
Seattle Times: Making it Fly
Then, on that August (1978) morning in Miami, (Frank) Borman surprised (Tex) Boullioun and other Boeing executives who had gathered at Eastern’s headquarters at the edge of the airport. Borman asked to see data on a hypothetical plane about 15 seats bigger than they’d talked about earlier.
Boeing officials, though not eager to increase the size of the plane, obliged and laid out the material for Borman, who was noncommittal.
Boullioun had to leave early, and Borman said he’d see him to the airport terminal. Once together in the back seat of the car, Borman told Boullioun he liked the bigger airplane design and was willing to gamble on it.
All at once Borman had a flash that a 175-passenger airplane was what Eastern wanted,”
Boullioun recalled. “He said, ‘If you’ll build that, we’ll go.'”
Boullioun replied: “You’ve got it.”
And so, with a handshake-just as the car jiggled over some railroad tracks-the Boeing 757 was born.
Boeing was anxious to get a launch customer. Once the airplane was launched, things did not improve.
Seattle Times: Making it Fly
For a long time, the 757 didn’t have any orders — and by some measures, it still doesn’t. The modest number of orders fed rumors of cancellation, as did nagging concerns that Boeing had blundered into making the airplane too large — at 178 seats, too close in size to the 210- seat 767.
“Some people felt the 757 wasn’t the right size for the market, this sort of thing. That the 150-passenger plane was the one,” said Benjamin Gay, who oversaw construction of the 757 for Eastern Airlines
The 757 broke away from its 727 roots solely by the synergies resulting from building the premier, new 767 at the same time.
Seattle Times: Making it Fly
The transformation effectively linked the 757 technologically with the new 767 rather than with the tried-and-true 727, the Boeing airplane the 757 was intended to replace. The changes were improvements, but they raised eyebrows.
The 757 sits in the shadow of the 767. The 737 was even further in the shadows, and would never emerge, effectively a branch in the Boeing development team.
Seattle Times: Making it Fly
“The 767 got the best of everything,” said a rank-and-file engineer on the 757 program, emphasizing the final word of the sentence. “They got the money. They got the appropriations. They got the management. Corporate gave them whatever they wanted. And we got what was left over.”
The 757 was to be a derivative of the 727, making it a comparatively low-cost program. The 767, which got an earlier start, was to be the all-new showpiece. It was to be, in the words of the 757 engineer, “Boeing’s baby.”
It seemed to some of those working on the 757 that their achievements were shrouded in obscurity and they were relegated to “me-too” status: Boeing had this great new airplane it was building, the 767. It was the first new Boeing since the 747 in the mid-1960s. It would be ultra-modern. It would be more fuel-efficient. It would be a great seller. And, oh yes, Boeing was also making this other airplane, the 757.
Human family traits are visible, the color of hair, tall, short. Animals physical traits evolve as they domesticate. The Boeing 757 changed its shape to accommodate the 767 flight deck layout to promote commonality. The narrow 727 nose section was replaced with a wider, more rounded section.
Figure 5. The Boeing 757 nose section was redesigned to accommodate the wider 767 flight deck layout. Source: Philip Birtles, Boeing 757.
The ME262 had one jet engine installed tight under each wing. Yet Joe Sutter, the legendary Boeing engineer, was probably not thinking of that when he proposed to install engines under the wings on the 737-100. Jack Steiner, 737 chief engineer, expected a T-tail derivative with two tail-mounted engines; it was just a smaller 727, after all.
Steiner’s decision to go with the 707/727 fuselage as a competitive advantage made the airplane a bit shorter than its competition, simply because at least one less seat row was needed. The proximity of the wing’s trailing edge and the resulting tail-mounted engine inlet created challenges with reliable operation and required structural compromises.
Putting the engines inside the wing, as had been done by others, was rejected. Damage tolerance was a large deterrent.
Sutter considered pod-mounted engines. Boeing had discovered pod-mounted engine mounts could be positioned favorably for the B-47, using the “broomstick in the wind-tunnel” technique. The B-52, 367-80, KC-135, 707, and 720 had all followed suit with pod-mounted engines. Pod mounted engines also damped out flutter, or instability in the wing structure itself.
Sutter considered how the smaller jet, operating more frequent cycles and in less-improved areas, would benefit by being low to the ground. A mechanic could service the airplane without always needing a ladder. A last-minute bag could be loaded by just running out to the airplane.
Sutter proposed to install the engines tight up against the underside of the wing, because traditional pods needed too much ground clearance and created challenges positioning exits. The resulting conventional empennage opened up the cabin to more seat rows. Sutter was named inventor on a patent for the concept.
The brilliance from Joe Sutter would ironically dog the airplane every step along the way.
The 737-100 Pratt and Whitney JT8D performed well during flight test, with only one engine needing to be changed out. The 747 Pratt and Whitney JT9D fared far worse; 55 were changed during the 747 flight test. The 747 does carry twice as many as the 737.
The CFMF56-3 had to be installed forward on the 737-300 and ended up with a flattened inlet.
Figure 6: 737-300 with CFM56-3 non-circular inlet cowl. Source: Wikimedia Commons.
The 737 NG used a new wing entirely, but still was pressed to fit the latest CFM56-7 engine.
Figure 7: 737-100 Vs 737-800. Source: Wikipedia
Top officials in Boeing Commercial Airplanes were cool to the idea of re-engining the 737 NG even as the engineers proceeding with a design.
Leeham News reported that at an employee meeting Jan. 14, 2011, Jim Albaugh, president of Boeing Commercial Airplanes, dismissed the neo and its potential competitiveness vs the 737NG.
“I think Airbus will find re-engining the A320 more challenging than they think it will be,” he told employees during one of his periodic “Excellence” meetings. “When they get done, they will have an airplane that might be as good as the Next Generation 737. We think we can continue to make incremental improvements to the 737 to make sure that it is a more capable airplane than even the re-engined A320.
“At the same time, while we haven’t made a firm decision, I don’t think we will re-engine the 737. It’s really hard to come up with a compelling business case to do that. We think the right answer to probably do a new small airplane that might come out toward the end of this decade. We’ll make that decision probably sometime in the middle of this year,” he said.
“Every customer I talk to has a real hard time understanding why a re-engined airplane makes sense,” Albaugh said
In a March 2011 interview with Scott Hamilton, Mike Bair, 737 product development head, said:
Boeing was focused on what a new airplane might be that would enter service in the “back half of the  decade,” around 2019 or 2020.
“We think there is a fairly compelling bundle of technologies we could put into a new airplane,” he said.
Engine technologies for the new, future airplane (which we’ll call NFA) could come from maturing the GTF, LEAP and Trent designs from P&W, CFM and Rolls-Royce, he said.
Boeing, in 2011, was looking at airplanes above and below 150 seats, which at the time was what officials liked to call “the heart of the market.” (Seven years later, this had moved to 162 seats.)
“I try to avoid saying ‘replace the 737,’ because what we’re doing is something a little bit different. We’re trying to figure out what does the world want in 2030, in 2035?” Bair said. “That’s when this airplane will be kind of at its prime. On the surface, it’s hard to image what worked well in 2000 is going to work well in 2030.
Boeing was indecisive about which direction to choose, Leeham News reported.
The ambiguity was driven in no small part during this era by the continued 787 debacle, which at the time of this interview, had not entered service.
By July 2011, when its hand was finally forced, the 787 was more than three years late, billions of dollars over budget and it hadn’t been delivered to any customer yet. Word on the street was that there was no way the Board of Directors would approve a new, clean-sheet airplane program under these circumstances. It had lost confidence in Boeing Commercial Airplanes and the Longacres executives to meet their promises, to keep a schedule and within budget.
The MAX was hastily launched in July 2011, when American Airlines informed Boeing it was about to place a record-setting order for nearly 500 airplanes. Airbus was lined up to snare it all with the A320ceo and neo families unless Boeing could make a credible offer.
Within 48 hours, Jim McNerney, then-CEO of Boeing, made the decision to launch the re-engined design of the 737. This later was branded the MAX.
It was a plane Boeing designed but didn’t want to build.
Once launched, Boeing had to play catch up to Airbus, which had a seven-month lead with its neo.
The MAX used the same wing as the NG, but the larger fan moved the engine forward and upward again.
Figure 8: The profile of the engines on the 737 NG (top) and 737 MAX (bottom). Source: Leeham News
The low standing profile surely is advantageous. The nose gear was lengthened by eight inches, but the main gear was unchanged. Longer landing gear have to go somewhere. It is a credit to the many engineering disciplines that Boeing has made each 737 model with the latest engines while retaining the stance. (The 737-10 MAX, still years away, has articulating main gear to accommodate the longer fuselage.) Of course, again, the 757 would much more easily accommodated the new engines.
Commonality acts as a moat barring the way into the kingdom. The toll to cross the moat is to pay back the cost of change in direct operating benefits. Airlines want to avoid pilot difference training, whatever the ultimate cost. Yet, almost all airlines have taken on more than one manufacturer of airplanes. There is no common type across suppliers. Regulators push the envelope, but suppliers work around them. What is the answer?
The 737-100 was designed for two-crew operation. A number of operators persisted with a third crew member after the airplane entered service. The use of fail-safe to prevent hazard from malfunction and dual systems to increase availability were designed to simplify pilot workload.
Consider crew alerting as a showcase of how, step by step, a focus on commonality, cost, and schedule, lead to a 737 decades out of step with every single competing airplane.
The original 737 models, now called the Jurassic by some, utilized a Caution Annunciator Panel to direct the flight crew to the appropriate control panel to diagnose system issues. Each system manages their own indications. The flight crew must prioritize their actions by assessing the situation and choosing which systems to attend to first.
Figure 9: 737-200 Caution Annunciator Panel. Source: Unofficial Boeing 737-200 Flight Crew Operations Manual.
The 757/767 spotlighted the quiet and dark cockpit. Normally, all lights extinguished. A central display with system synoptics and message priorities.
The 757 was a two-crew airplane. Boeing pioneered Engine Indication and Crew Alerting System (EICAS) for the 757 to simplify the pilot interface when addressing non-normal situations. EICAS was a great success. The 767 adopted EICAS in its decision to go two-crew as well. In this case, the 757 led the 767. The 757 entered service in 1983. Every Boeing airplane built since then uses EICAS, except the 737.
The 737 Classic was built after the 757.
For reasons of commonality, the 737 Classic “idiot light” caution annunciator panels were retained. The Classic included EFIS as an option. Many airlines also retained the “steam gauges,” of mechanical instruments, for commonality.
The original 737 was already holding back the Classic. Both followed the same panel installed on the Boeing 367-80, which first flew in 1954.
Figure 10: Boeing 367-80 (precursor to KC-135 and 707) flight instruments. Source: Boeing 367-80 Jet Transport Panorama.
Figure 11: Non-EFIS 737-300. Source: b737.org.uk. Note the annunciator panel for automatic flight control mode on the upper left.
The concepts that led to the Electronic Flight Instrument System (EFIS) were initially developed on the very first 737, NASA 515. The 757/767 were first to market with EFIS. A prominent difference with EFIS Vs. non-EFIS is the integrated mode display along the top of the upper display, a huge improvement in automatic mode awareness.
Figure 12: 737-300 EFIS: Source: b737.org.uk.
The MD-95 become the Boeing 717, entering service in 1999 with an advanced alerting system.
Boeing Aero: 717 Advanced Flight Deck
A highly integrated, advanced alerting system replaces most conventional indicator lights, warning lights, annunciator panels, and other dedicated indications.
The alerting system consists of the Engine and Alert Display (EAD); system displays; the master warning, master caution lights; and the central aural warning system.
When a condition requiring an alert is detected, the VIA displays the alert, illuminates the master warning or master caution light if required, and sounds an appropriate aural warning.
The flight crew acknowledges the alert by pressing the lighted cue switch on the systems control panel (SCP), which displays the appropriate synoptic display.
If a checklist procedure is required, the flight crew refers to the abnormal checklist to accomplish the required corrective action.
The 737 NG started development in 1993. That follows the 767, 757, A320, 747-400, MD-11, and A330/A340. The 777 and MD-95/717 were in development. The Caution Annunciator Panel has filled out since the 737-200 but is identical otherwise.
Figure 13: 737 NG Caution Annunciator Panel. Source: Unofficial Boeing 737-800 Flight Crew Operations Manual
The 737 NG lack of managed alerting is remarkable. Once again, airline concerns over commonality, and the inherent simplicity of idiot lights was compelling. Since steam gauges were not an option, Boeing simulated steam gauges on the glass to satisfy airlines wanting to minimize differences with pilots still flying the 737 Jurassic series.
Figure 14. Southwest 737 NG with steam gauges on glass. Source: airliners.net
Boeing Common Display System offered the complete flexibility to take on the features of old or new. Boeing described this in a company periodical.
Boeing Aero: The Next Generation Flight Deck
The next-generation 737 airplane (737-600/-700/-800/-900) offers more advanced, even more reliable airframe systems and digital avionics for increased altitude, speed, and range capability.
Key to the next-generation 737 is the computer-generated graphic representation of flight instruments on the common display system (CDS).
Simply by loading flight-deck software, operators can use the CDS to replicate either the electronic flight instrument system with map (EFIS/MAP) display of classic 737 models (737-300/-400/-500) or the primary flight display/ navigational display (PFD/ND) used in the 777 and 747-400 models.
As a result, operators can continue to fly their earlier 737s while introducing next-generation 737 airplanes into their fleets with minimal training.
Operators who fly the latest 737 exclusively will find the more advanced PFD/ND display formats are aligned with those on the advanced 747-400 and 777.
In order to duplicate the functionality of the 737-300 flight deck, any change to its integral presentations had to be minimal in the following displays on the next-generation 737 flight deck:
The FAA’s Flight Standardization Board ruled that simply “transitioning from CDS EFIS/Map to PFD/ND in the -600 through -900ER series group the minimum training requirement has been determined through testing to meet C level training.”
Yellowstone 1, or Y-1, was to replace the 737 family. The study ran from about 2004 to 2008. Issues with downsizing 787 components and composites chilled the project.
Airbus announced the A320neo series in 2010 and Boeing was faced without a new airplane to match.
Realizing that the fuel gains were the main motivation, Boeing launched the MAX in 2011 as “Min to the MAX” to restrict changes from the NG to only those mandated to meet the performance or to install the engines.
Figure 15: The year after the 2011 program launch, Boeing promoted the MAX as the “same” as the NG, including simulators. Source: Boeing
Boeing considered the certification risk of continuing with idiot lights and chose to retain them instead of the effort and risk to revise the alerting system altogether which would then create significant differences with all other 737s.
Figure 16: 737 MAX Flight Deck, Caution Annunciator Panels are shown on the upper left and right, on the glareshield, with master warning and caution illuminated. Source: wraltechwire.com
The 737 MAX has the same Caution Annunciator Panel design from the 737-100. The website Aviation Today wrote:
Since winning the Max display contract from Boeing in 2012, Rockwell Collins has worked with the Original Equipment Manufacturer (OEM) to effectively mimic the cockpit package featured on the 787. Engineering teams at Boeing and Rockwell Collins worked to replace, revise and relocate 23 displays and controls, and the Max design also reduces the six-display configuration of the 737 NG to four 15.1-inch Liquid Crystal Displays (LCDs).
“The clocks, which were standalone pieces of equipment in the cockpit before, have now been incorporated into the displays. There are separate switches and functions in knobs that have either been relocated or incorporated into the displays, as well. Those changes were made to accommodate for the four large screen displays in that smaller cockpit. Generally speaking, regarding what is in the Max versus what was in the previous Next Generation version of the airplane, everything is the same, it is essentially in the same location, which was all part of Boeing’s plan to simplify the transition between the NG model airplane to the Max,” Keith Stover, principal systems engineer at Rockwell Collins told Avionics Magazine.
From submittals gathered by the US House, Boeing recognized the best solution and the most practical solution.
Figure 17: 737 MAX EICAS Risk Review. Source: US House-Boeing Submission
Figure 18: 737 MAX EICAS Risk Review. Source: US House-Boeing Submission
Figure 18: Exemptions sought by Boeing from the FAA. Source: Seattle Times.
Figure 20: 737 models compared to other airplanes, noting fly-by-wire and centralized crew alerting. Source: Peter Lemme.
The 737-100 went through quite a bit of tweaking as it evolved to the 737-200 ADV. The 737-100 started with much higher drag and stall speeds than expected. It had a pitch-up at stall. It had “stick lightening” at high Mach numbers. The changes to correct the deficiencies from the start of flight test to delivery (737-100) included:
The aerodynamic center of the wing shifts backwards when transonic, in part due to shock waves that form along the leading edge. The lift shifting backwards causes the airplane nose to drop, which if unchecked, will cause the airplane to accelerate further, worsening the tendency. This is called Mach Tuck. The pilot must pull back on the column to keep the nose from dropping as the airplane accelerates. Mach Trim applies an offsetting control input to compensate for Mach Tuck.
Movable Stabilizer restores X-1 pitch control. Source: chuckyeager.com.
Then, during his eighth flight on 10 Oct., he lost pitch control altogether, as a shock wave formed along the hinge line of the X-1 elevator. He reached Mach 0.997 but without pitch control it would have been foolhardy to proceed. The X-1 had been designed with a moving horizontal tail and Capt. Jack Ridley convinced Yeager that by changing its angle of incidence in small increments, he could control the craft without having to rely on the elevator. This had never been attempted at extremely high speeds but Yeager was game to give it a try on the next flight.
The 737-100 discovered the need for a Mach Trim function during flight test. An actuator was added to the elevator feel-centering unit to apply a small elevator bias as a function of Mach number.
The 707 had a Mach Trim function that applied a small amount of stabilizer trim.
The 757, 767 and 747-400 use stabilizer for Mach Trim function.
The 757, 767 and 747-400 models adapted the same Speed Trim System used on the 737 to include a Mach Trim schedule as well. These models implement the Mach/Speed Trim System in a two channel, dual lane (ARM and COMMAND) with dual inputs manner. In contrast, the 737 Speed Trim System (later with MCAS) was originally implemented as an active/standby two channel, single lane, single input manner.
The 707 also had a stick-nudger installed in some cases, which effectively pushes the control column forward with a modest force, less than 10 lbs. The stick nudger is operating on the elevator to offset pitch-up.
The 747-100/200/300, the 767, and the 747-8 all have some form of stick nudger or pitch augmentation that operates on the elevator.
The following figures show the 767 stick nudger, which is attached to the elevator feel and centering unit.
Figure 21: 767 Elevator Control System with Stick Nudger attached to Elevator Feel and Centering Unit. Source: Unofficial Boeing 767 Airplane Maintenance Manual.
Figure 22: 767 Stall Warning Components. Source: Unofficial Boeing 767 Airplane Maintenance Manual.
Figure 23: 767 Stick Nudger Description. Source: Unofficial Boeing 767 Airplane Maintenance Manual.
Figure 24: 767 Stick Nudger. Source: Unofficial Boeing 767 Airplane Maintenance Manual.
The 737 Mach trim is attached in almost exactly the same manner as the 767 stick nudger.
Figure 25: 737 Elevator Control System with Mach Trim Actuator attached to the Elevator Feel and Centering Unit. Source: Unofficial Boeing 737 Airplane Maintenance Manual.
The original 757/767 design included a pitch augmentation system that operated on the elevator but was removed prior to delivery.
Every Boeing model, other than 737, has used augmentation on elevator controls to counter pitch-up.
The 737 MAX uses elevator for Mach Trim and stabilizer for Pitch Augmentation.
Every other Boeing airplane uses elevator for Pitch Augmentation (if required) and stabilizer for Mach Trim.
Figure 26: Pitch Augmentation using Elevator Vs Stabilizer. Source: Peter Lemme.
Figure 27: Mach Trim using Elevator Vs Stabilizer. Source: Peter Lemme.
It is not known if Boeing considered moving the 737 MAX Mach Trim function to the Speed Trim System (as done on the 757, 767, 747-400) and redesign the Mach Trim actuator as a stick nudger. Adding Mach Trim to Speed Trim System would have driven some form of Fail-Safe design.
There were redacted sections mentioning other methods to manage pitch-up which remain unknown. The 737 MAX final configuration included:
Malfunction is inevitable. The hazard from malfunction can be managed. The objective is to minimize the crew workload in response. Fail-safe systems trade protecting the pilot from the effect of malfunction to the effect of loss of function. Redundancy can allow for Fail-Op, if continued functionality is required.
Logical limits are the result of executable software and computing. The reliability of software is associated to the level of hazard it exposes. If the hazard is greater, the software has to be better; as in more documents, more analysis, and tested much more rigorously. Much credit is taken for software to protect from malfunction, but when software itself malfunctions, anything is possible.
Electrical limits are the result of component failure. The hardware can be designed with tandem components, or gates, such that any one gate stuck open won’t cause a malfunction. Removing power should disarm all functional outputs.
Mechanical limits afford the next backstop, where the actuator has only a limited “throw”. The 767 stick nudger and the 737 Mach trim actuator have limited mechanical authority, no matter how they fail. The 737 Yaw Damper was once thought to be the source of catastrophic lateral upsets, but analysis showed its authority was too limited (the issue was in the rudder).
The last backstop for malfunction is the pilot. The pilot must recognize the situation, formulate a response, and take action. In the case of stabilizer runaway, the pilot has no more than four seconds to stop the runaway from its unexpected onset.
Elevator augmentations have mechanical limits that restrict malfunction without any pilot action.
Autopilot stabilizer trim malfunction:
The risk from logical limits is based on software Design Assurance
The risk from electrical limits is based on adding tandem components in a Fail-Safe manner
The risk from reaching mechanical limits is entirely up to the flight crew.
Stall Identification is an augmentation to encourage a nose down pitching moment at the stall break point. The 737 is the only Boeing model that lists stall identification as a function in its Flight Crew Operations Manual.
Figure 28: 737 NG Stall Identification. Source: Unofficial Boeing 737-800 Flight Crew Operations Manual.
The high alpha mode drives the stabilizer continuously Airplane Nose Down (AND) until a washout gain (-2.5 units) or by the aft column cutout.
Source: Unofficial 737 Airplane Maintenance Manual
The stall detection circuit monitors the flap position and the angle of airflow. Near stall, the speed trim function trims the stabilizer to a nose down condition to allow for trim above the stick shaker AOA and idle thrust. The trim continues until the stabilizer gets to its limits or the aft column cutout position is exceeded.
Once the high alpha mode is released (by AoA going below the reset threshold), speed trim will trim Airplane Nose Up (ANU) as the airplane accelerates.
The 737 NG High Alpha mode, as part of Stall Identification, operates even more aggressively than the 737 MAX MCAS. It appears to be a single sensor application. With no service issues to draw from, there does not appear to have been any significant issues with a single AoA sensor triggering an Airplane Nose Down (AND) stabilizer runaway. There are some interlocks.
Source: Unofficial 737 Airplane Maintenance Manual
The gain is 100 percent for an average N1 more than 80 percent or zero for an average N1 less than 60 percent.
The gain is 100 percent for a Mach less than 0.5 or zero for a Mach more than 0.68.
Figure 29: 737 NG Stall Identification using Elevator Vs Stabilizer. Source: Peter Lemme.
The FCC controlled neutral shift region (FCNSE) appears to be a unique feature for the 737 taking advantage of the Mach trim actuator. The primary function of the flight control computer (FCC) controlled neutral shift is to reduce the pilot column force necessary to trim the airplane during initial climb out after takeoff with a forward CG and both engines operating.
The Mach trim actuator can trim the elevator 4.7 deg Airplane Nose Up and -1.65 deg Airplane Nose Down.
The 737 MAX incorporate other sophisticated functions. A fly-by-wire spoiler system was programmed to improve handling. Load alleviation relates to distributing the load across the wing. LAM = Landing Attitude Monitor is designed to prevent tail scrapes. Elevator Jam Landing Assist uses the spoilers to enable a flare.
Figure 30: New 737 MAX Features. Source: 737 Flight Standardization Board Report.
The following figure traces significant features as they evolved from the 737 Jurassic to the 737 MAX. Those features that required changes for return to service are highlighted in red (airworthiness directive).
Figure 31: 737 Technical Heredity. Source: Peter Lemme.
UK ARB Certification Test Pilot D.P. Davies found that the FAA certificated the 727-100 with a pitch-up into a stall based on Boeing professing “equivalent safety”. He questioned his FAA counterpart on what was found equivalent and got nothing in response. Davies enforced strict compliance to a specification that no one disagreed with. What was at stake was that the Boeing/FAA agreement professed handling qualities “good enough” but not “to the letter”.
Equivalent safety is applied to an alternate means of compliance to meet the expected standard, not to argue that the standard is just a guideline.
The British ARB insisted on installing a stick pusher to protect from a “deep stall” and for stall identification.
The same issue came up with the 727-200, and Davies lost the decision. There was no stick pusher on the 727-200 and it was eventually removed from the 727-100s as well.
The 727 has powered elevator actuators and can be flown out of a deep stall, as Lew Wallick demonstrated through inadvertent encounter. Deep stall did not emerge as a common finding with 727 accidents.
A stick nudger was added to the 747-100 in yet another difference between the US FAA and the UK ARB. The pitch-up issue had been accepted by the US; the UK insisted on the stick nudger. The 747-400 replaced the stick nudger with speed trim system, the same system that was installed on the 737-300 classic in 1984.
The 757 and 767 were both initially developed with a Pitch Augmentation Control System (PACS) to offset a pitch-up. Vortex generators on both models, a stick nudger on the 767, and countless other aerodynamic tweaks, collectively, provided adequate flying qualities. PACS was removed from both airplanes before either was delivered.
TWA Skyliner Magazine, 1982-08-02, TWA Pilots Fly the Boeing 767
We went to 37,000 feet and accelerated to Mmo (maximum operating speed) and rolled the aircraft into a steep bank, pulling close to 2.5 g’s and, although the pitch augmentation had been removed, the addition of seven vortex generators on each wing seemed to correct what we understand had been an adverse stability condition. The aircraft was stable and “honest” throughout the high g/high Mach maneuver. Full stalls in all configurations were accomplished at 10,000 feet with the stick shaker turned off. This aircraft was not equipped with the proposed stick nudger but the aircraft seemed to stall with no adverse characteristics. (Ed. note The “stick shaker” is a warning device which senses a stall build-up and accentuates vibration before a pilot might feel the actual stall condition on the yoke. The “nudger” automatically presses the nose of the plane down to· forestall a stall.)
Boeing Stability and Control judged the 737 MAX flying qualities as unacceptable. They rate it a “Major” hazard if high-alpha flight is encountered while the MCAS system is not available. A Major hazard is well within the capabilities of every pilot to overcome. The vigor of the pitch-up should not be judged as a substantial threat to the safety of the airplane.
Major hazards are routinely managed successfully in isolation. Major hazards become much more challenging when multiple hazards arrive at the same time, consuming margins in workload and attention.
The 737 MAX handling qualities, with MCAS functioning as designed, were considered sufficiently similar to the 737NG. They share the same wing, which certainly is a substantial factor in their similarity.
AC 25-7C is the “Flight Test Guide for Certification of Transport Category Airplanes”, revised in 2012 and used for the 737 MAX. An Advisory Circular provides acceptable means for compliance.
A gauge for flying qualities provides three passing grades (Satisfactory, Adequate, Controllable) and one failing grade (Unsatisfactory).
Figure 32: Pilot Induced Oscillation (PIO) Rating Guidelines. Source: AC 25-7C.
AC 25-7C provides the minimum flying qualities based on atmospheric disturbances, flight envelope, and likelihood of the condition (where anything less than 1E-5 is improbable). The failure of MCAS in the Operational Flight Envelope was considered Major. The pitch-up is in the Operational Flight Envelope.
AC 25-7C teaches that the flying qualities can degrade under improbable situations by one notch but may not become unsatisfactory. MCAS failed in the operational flight envelope is considered Improbable, and for light turbulence, the handling qualities may be no worse than Adequate, which is well within the expected skill of a pilot qualified for the airplane.
Figure 33: Minimum Handling Qualities (HQ) Requirements. Source: AC 25-7C.
Aviation safety hinges on pilot response to malfunction and loss of function. The greatest challenge is to take a bad situation and not make it worse. Reducing the level of automation during malfunction should be the first step, often the most reluctant.
The 737 has embraced a reliable and straightforward alerting system but fails to manage alerting under multiple failure scenarios, where the flight crew are most stressed, shunning using capabilities evident 40 years ago.
The 737 was born in a time of analog computers and circuitry. System failures were frequent. Pilots expected the unexpected. The 737 simplicity and elegance provided a stable foundation that never wavered over four generations. While the instruments moved from dials to glass, the hardware to software, the core of the 737 became fully integrated and incredibly reliable.
The 737 should have stopped at the 737-500 and the 757 should have picked up the trail into the twenty-first century, except that the launch customer had made the 757 too big. Without a replacement, the 737 just kept getting new engines. Customers wanted commonality. What they got was the least common denominator.
The 737 is an oddball in the Boeing fleet. The choice to put MCAS on stabilizer and Mach trim on elevator, when the opposite was used everywhere else, is puzzling. Limiting malfunction on elevator can be achieved through hard, mechanical limits. Limiting malfunction on stabilizer that relies on the pilot to take action means that they can be overcome if they don’t.
A close look at the findings and analysis leading to return to service. What went wrong? What is the corrective action? What’s missing? What’s next?
Peter Lemme is a pilot, engineer, and writer with over 40 years of experience in the aviation world. He draws on his expertise in aviation history, aeronautics, automatic flight control, data link, and satellite communication; to provide insight into the performance and safety of aircraft systems, the human interface, and flying.
Thanks for providing this free of charge Scott. This looks like it’s going to be a good long read to help get us through a dark winter. Covid-19 mental health support service.
Whoooee, Ask and you shall receive and then your brain hurts.
I am going to need mental health services trying to absorb it all.
One comment on nomenclature and no knock on Peter, its a Boeing stupidity
Classic should refer to the original 737-100/200 not the follow up 300 etc. Its from the computer world where the first generation of a system is known as the Classic.
Airbus did the same thing when they changed the name of Winglets (have you ever seen a shark with two parallel fins?)
I believe that the original 100 /200 are known as Jurassic
The problem with product iterations that are designed to require minimal re-certification per iteration is that you just keep postponing the inevitable. The result is a dinosaur in the modern era. Consequently, a modernized FBW narrowbody from Boeing (if it ever comes) will be so different to the current product that — from a pilot re-training point of view — operators might as well just switch to a product from another OEM. Customers such as Southwest may choose to start making that switch now rather than later, by (partially) defecting to today’s A220.
Availability of product was an issue at one point and will not be for a bit.
Reality was production at one point was all taken and better to have some sooner than latter.
That is why a me too A320 does not cut it, you need a game changer. I don’t see that in Boeing future.
Calhoun can kick the plane down the runaway until he retires with his ill gotten gains and then the next guy or gal looks at it figuring out how to game whats left.
> That is why a me too A320 does not cut it, you need a game changer. I don’t see that in Boeing future.
A good call, in my opinion. The recent article (was it Aboulafia?) talking about “retaining commonality” w/
the present 737 fuselage shows precisely *what’s not*
going to work; er, fly..
Wouldn’t you say always waiting indefinitely for a “game changer” is what got Boeing Southwest etc into this place in the first place. Boeing could have replaced both the NG 20 years ago and the MAX several years ago and had an aircraft with better technology than the A320. I would say a lithium aluminium fuselage with a composite wing and B787 style “game changers” systems such as not using bleed air. It would probably have had a wider single aisle that would have allowed a person to pass a service trolley and had A320XLR game changer range.
Southwest has gotta realize it cannot bet its future on one type and the A220 is the perfect 737-700 replacement. With the current state of the business, they have the choice of upgauging or paying a huge efficiency penalty to stick with 737. The subfleet will be pretty large as well.
Just read the new article by Dominic Gates referenced in the LNA Twitter feed: see link below.
Of particular interest is the following passage:
“Last February, knowing the grounding of the 737 MAX would likely mean another year of very poor financial performance, Boeing’s board changed the structure of the company’s incentive plan. Instead of basing targets largely on profits, the financial goals were tied to the timing of the first delivery of a 737 MAX after its ungrounding by the Federal Aviation Administration (FAA).”
In other words: as regards the MAX ungrounding, employees were offered an incentive based on *speed* rather than quality/thoroughness of re-certification.
Nothing has changed.
That is a mischaracterization. Boeing knew there would be no profit, therefore no profit sharing with employees, in 2020. So they linked bonuses to the MAX RTS, which was an achievable goal, and would produce bonuses for 2020.
Boeing had no control over the timing of RTS, it was entirely dependent on the regulators. The incentive program set up a goal which would benefit both employees and the company.
Nor was there a trade-off between speed and quality or thoroughness, since only the regulators could determine what would be acceptable for RTS. Regulators were absolutely clear, throughout the entire process, that speed was never a factor in their decision, there was no timetable. They looked only at safety and thoroughness.
That is what Boeing had to demonstrate for RTS, and did. And now the employees will receive a bonus, which is only a good thing. There is no negative context here.
They looked only at safety and thoroughness.
That is what Boeing had to demonstrate for RTS, and did. And now the employees will receive a bonus, which is only a good thing. There is no negative context here.
Why then was it seen as prudent by Boeing to “prime” testers in the RTS formalities?
IMHO your are not only putting lipstick on a pig .. you are encasing it in layers of lipstick.
Uwe, we’ve covered this before. The Boeing test pilot reminded the FAA test pilot in July 2019, to correct for MCAS when simulating the accident scenario. The FAA test pilot did correct, and recovered, as did all the pilots in that particular test. Had nothing to do with the certification flights in 2020, or the bonuses awarded for 2020.
“Boeing had no control over the timing of RTS”. This is an extremely good reason why it was a totally unsuitable measurement for a bonus payment.
Since thoroughness was a criterion of regulators, a bonus for thoroughness would be valid. The goal was recertification as defined by regulator requirements. Speed was a conjecture made here, rather than a requirement. The bonus was perfectly suitable.
Uwe, thanks for reminding us of the cooked re-cert flights.
Priming test pilots to “keep the finger on the pickle switch” is a sign of (at least) two gross shortcomings, namely:
– A complete lack of scruples as regards trying to bias the outcome of the certification process;
– A plane that is so unstable that pilots have to be primed to be constantly alert to the occurrence of serious issues.
IMO Boeing needs all the talent they can get now, They didn’t pay them Bonuses last year. I think developers and engineers at Boeing would need an incentive to stay.
I am not completely against this simply because most of the employees got Bonuses, now had it only been Management that would be a prime example of greed
An excellent and thorough analysis which requires careful reading. Thank you !
The choice of MCAS pitch augmentation with stabilizer was driven by development experience with the KC-46 tanker. It preserves elevator authority for the pilot, and also consolidates trim functions in the stabilizer.
Trim is a form of inner autopilot, it controls the position & attitude of the aircraft in the air. The conventional outer autopilot controls the path of the aircraft in the air. Utilizing separate surfaces for these is a valid design approach. Ideally the pilot does not need to be concerned with the inner control loop, while focused on monitoring the outer control loop, which retains full control authority.
MCAS wasn’t a poor design choice so much as a poor implementation, as is now well-documented. I’m sure Peter will enlighten us on that in the second part.
Although it looks like MCAS may not have been needed at all for flight, but purely for certification.
If this really is the case, certification needs to be looked at. If certification ends up adding an additional layer of complexity that introduces more possible points of failure, I think there’s certainly scope to examine certification if your goal is to increase flight safety.
Balance the need for training regarding the pitch moment curve against adding a complex system, which ends up being the safer option ?
Yes, boeing was stuck in the certification rules and could not switch to simulator training for non-linear stick forces.
I don’t think there is a certification issue. Needed for flight and certification for flight are legally the same thing. The rules exist for a reason. The reason remains valid.
The system designed to meet the regulations was done poorly. Had that not been the case, none of us would have ever heard of MCAS. We’ve seen that MCAS can become a safe system.
If Boeing had applied for an exception (additional training in this case), and eventually the exception caused an incident, then the criticism would be, as we’ve heard here many times, of not meeting the rules and grandfathering.
Further there is no guarantee that initial training for an unlikely circumstance, would mean anything years later. That was one of the lessons of the MAX accidents (and others), and is why recovery training will now be recurrent every 3 years.
In my mind, the issue was the belief that this minor corrective system did not merit the same scrutiny as other more critical systems. Further the scrutiny became less as the system evolved to become more complex and powerful, instead of greater. And the belief that pilots were a fail-safe endpoint in the fault tree, instead of being branches of their own.
That goes ultimately to safety culture and design principles, and is what’s changing now.
The rules are there, but if you compare a non-linearity but still stable aircraft that you train on vs. MCAS hidden in the software that you were not given information and training on.
It reminds me on the MD-80 Automatic Thrust Restoration system and the SAS MD-80 accident were that automation was hidden and the pilots were not aware nor trained on it that caused troubles after clear ice ingestion and engine surges.
Another is Asiana 214 777 speed trap crash.
Well intended automation hidden into the aircraft systems can bite back and there has to be a delicate balance between complexity and comfort.
Do we know definitively when the decision to add MCAS was made? I.E. was this after wind tunnel testing, or simulator testing or did Boeing actually fly a MAX test aircraft without any form of MCAS, and discover the issues at that point, and then add MCAS after discussion with the FAA?
I’ve read various pieces of information on this, but would really like to know exactly when the decision was made to add MCAS.
A precise timeline would be very helpful.
Jakdak, this has been discussed at length here, and is documented in a NYT article, in the IG report, and the DOT report.
The discovery of the need for pitch augmentation was made very early on in the simulator in 2012, and the wind tunnel testing for various ways to resolve it was also made about that time. MCAS was listed in the ATC application approved by FAA in March 2012, so the initial decision had been made by then. Notably, this was the high-speed version of MCAS
MCAS continued to be revised and tested in the simulator between 2012 and 2016, with reports made to the FAA. At that time, the FAA retained the certification basis for MCAS.
In 2016, things began to happen in quick succession. The MCAS fault tree analysis was completed January 19, for the high-speed version. First test flight conducted January 29.
March 2016, FAA issues the TIA, and Boeing introduces MCAS revision D, which adds the low speed case to MCAS. On the same day, MCAS is removed from the FCOM and FSB training materials, based on evaluation of the earlier low-speed version of MCAS.
Note this is the source of the Forkner “I lied unknowingly to the FAA” comment which led to the fraud charge. Forkner had not seen revision D when he campaigned to remove MCAS from manuals and training materials. When he became aware of it later, he did not disclose to the FSB/FAA. Boeing had disclosed Revision D to the FAA, as the FAA still retained control of the certification basis at that time, and it was necessary to revise the flight test plan.
April 2016, the FAA begins flight-testing the MAX. May 2016, FAA conducts flight testing of MCAS, both high and low speed scenarios. August 2016, final revision of flight software revision E is released.
September 2016, FAA delegates the certification basis for MCAS to Boeing ODA.
November 2016, flight testing of MCAS is complete. March 2017, ATC certification granted.
The choice of MCAS pitch augmentation with stabilizer was driven by development experience with the KC-46 tanker.
For the MAX ( a basic 737 with repeat mommy makeovers )
this was an unsuitable method applied to an unsuitable object.
( 767 is not aero compromised the like the MAX is, data input assumptions on the 767 tanker clash with the systems philosophy of the 737. 767 provides synthetic/marked good data input )
And yet MCAS has been approved by the regulators and is now certified as safe, with needed modifications. Not found to be unsuitable, as the MAX was not found to be unsuitable.
The design from the KC-46 was not directly portable to the MAX. The new design was poorly done and implemented, but the concept was applicable and remains so.
The MAX has been “found to be unsuitable” in China: still sitting on the ground, corroding slowly, with no sign of certification any time soon.
That’s 40% of the world market.
Poor Boeing 🙁
Obviously China being the political bully at large.
Without cause. …
Ask the B-guy. 🙂
> And yet MCAS has been approved by the regulators and is now certified as safe
They’ve never failed us before, now have they?
Can you say “regulatory capture”?
EASA, Canada, Brazil also participated in the approval of MCAS. So the “regulatory capture” must be worldwide, for your assumption to be valid.
It seems this was to correct a ‘fault’ in the 707- 300 and 400 series ( Conway engines)
“Davies noted that with the first stage of flap selected, the aircraft had a tendency to pitch up just prior to entering the stall. This was determined to be caused by the inboard leading edge devices, peculiar only to the 707-3/400 series which, when extended, effectively retained lift to higher angles of attack, and moved the Center of Pressure forwards, causing the nose to pitch up. ..”
“The 737 is an oddball in the Boeing fleet. The choice to put MCAS on stabilizer and Mach trim on elevator, when the opposite was used everywhere else”
This quote from Lemme seems to imply that MCAS on the 767 was on the elevator.
the 767 design included Pitch Augmentation Control System (PACS) on elevator – but it was removed by installing vortex generators. It does have a stick nudger – on elevator.
Yes, MCAS on KC-46 was on stabilizer, but that was not pitch augmentation, it is more of automatic mode. Regardless, I agree I should acknowledge KC-46 MCAS, thanks.
Hi Rob, thanks for the comment. The application of MCAS on the KC-46 has never been very well described, but I understand that the point is to maintain trim while offloading fuel which is manually flown, as a workload reduction. There is no expectation for mistrim in the sense that it would be holding trim in stable conditions, not stepping in a command to offset a nonlinear pitching moment. The 767 stabilizer system is entirely different, but that is not the big issue. On the KC-46, there would be no reason to disable either column cutout. That means any malfunction is easily managed. MCAS override of the aft column cutout was a huge fracture in the safety balance that MCAS 1.0 just ignored. It was never appreciated. the safety analysis just said the pilot would trim in opposition to make up for it.
Thanks Peter, I agree the purpose of MCAS was wholly different for the KC-46. Only the basic concept of trim control was common. Also about the sophistication of controls and implementation on the 767 vs the 737. Had that been equal, there would not have been an issue on the 737.
the removal of the aft column cutout would have the same effect, not stopping airplane nose down trim.
e.g. 767, alternate trim still available, in cutout scenario, no ET302 binding.
“If the malfunction is unique to the electric trim control, full trim rate is available by using alternate trim.”
Nice to see how well Peter Lemme’s analysis chimes with other analyses by known pilots. For example:
– Bjorn Fehrm, who described MCAS as “absolutely unforgivable”.
– Chesley Sullenberger, who described the MAX as “not up to modern standards”.
Interesting to see in Table 1 of the 777X article below that the number of “firm” MAX orders currently stands at only 3282, after 749 ASC606 deductions (18.5 % open order erosion). Add in the 387 that were already delivered and you get 3669. In contrast, the order list for the A320 neo family is showing 7451 (with 1617 delivered) — more than twice the MAX figure. Add in the orders for the A220 (630; 143 delivered) and it becomes clear that:
– Airbus is wiping the floor with Boeing in the NB segment.
– An ever-dwindling percentage of airlines want to associate themselves with the archaic technology in Boeing’s “flying dinosaur”.
I would suggest this variant has to do with Boeing split community of the 737 and the Wide Body factory.
As Boeing continue to break up those relationships between engineering and the factory and the models, we can understand why so many problems occur in so many areas.
I saw it in my last 25 years or working.
2. Parochial: It was all about the Silo performance and the layer in the silo, not anything to do with the company as a whole or doing it right.
Rather than a pack of dogs it was each neighbor let their dog out and it was a dog fight on a massive ever widening scale.
The mild term of it was.
Teamwork: Hooray for me and the heck with you.
Corporate America: Love it or shudder at it.
It is going to take me several days to read through this – thanks.
One observation I can make is that among committed technology people the is often found a belief that a newer, redesigned system is always better than a system that started from an older base and changed through iterative redesign. Sometimes a clean sheet design is better, but there is no inherent natural upward curve of technology that guarantees new clean-sheet designs are necessary “better”, and there are many examples in software systems where a clean-sheet redesign of a large system turned out to be a disastrous failure. The historic Bell System had a number of notorious failures through redesign, and IBM mainframes notable run core code that was perfected in the 1960s and requires an act of Gaia and Lady Ada Lovelace to authorize a change control.
…however, there comes a point where old designs just don’t cut it any more, and you need to take the plunge and develop something new.
Otherwise we’d still be using steam engines and sailing ships, and biplanes with cloth wings.
back in the day shockingly when the steam turbine unshelved the triple expansion engine.
As sPh says I quit halfway (job & stuff) but certainly an interesting piece of info. May split it out a bit more into smaller subassemblies.
Recognizable is (Albaughs) believe and faith the 737NG is so good, the NEO won’t be a problem and customers will wait. Any engineer / marketing guy worth his salary could see the Airbus BPR/sfc, AKH, A321, engine choice would have market impact. Had Boeing exec’s ended up in echo rooms or were they still pararlized and risk averse because of by the 787 dramas?
Interesting to read the 757 story. If Boeing in the nineties had invested to combine the 757 cockpit / systems with the NG wing and create space below the wing, Boeing would be in a totally different system today..
Some say the RB211-535 shop visit bills and the old design wing killed off the 757 as the A321 grew in range thanks to winglets and its much cheaper Engine shop visit bills. Still Boeing could have designed a new wing, reduced empty mass and ordered new Engines. Still those Engines would be ophans with no other application. PWA was is no good shape those days with both PW2000 and PW4000 problems and RR was living off the RB211-535, so no easy task telling CFMI to design a new 37k Engine back then. Don’t know if Boeing did try it?
the engines lead the airplane, for sure.
it would be fun to go back and plot all the candidates as they emerged to see if any interesting trends.
excessive (paradigm) wrappers and curlygig additions create traps.
At some point you have so many layers and warts the system turns opaque to introspection.
The proper way is to extract knowledge gained and create from new with that improved knowledge.
A case in point is what happened with AF447.
With automation implemented half assed and not understanding or testing your pilots in their reactions, you wind up with a miner issue being turned into a full stall and no one recognizing it (its not even 100 level flying, if the hose is up at 20+ deg you are in stall territory and a 10,000 FPM decent rate confirms it)
Until Boeing made the lethal MCAS 1.0 variant, the 737 had an equal safety rate to the modern A320 approach .
In the case of Airbus you could make a pitot loss at altitude a non event with a ding, and it puts the aircraft into the right power setting and attitude to ride through it.
The core problem is the pilots got used to it doing everything for them and it was lost they were pilots.
Training is now done to help correct that but no one does human factors reaction before this stuff, just after.
Much like AOA vanes, they had a whole library of pitot loss and something like 13 incidents all of which were handled wrong and none was the basic revert to the memory item of 85% power and 5 deg up nose.
As a pilot I find that appalling.
If your pitot acualy quit at 30,000 feet, you just ran into a mountain. It can’t do that, ergo you have a system issue.
But the reaction was either yank back (insane) or push forward (some logic to regain airspeed but how do you loose all airspeed in a mili second?
Answer is you don’t and you look to maintain, maintain, maintain until you sort it out (mostly like frozen Pitot)
Human factors are long gone from what they are putting in the cockpit.
Equably like instrument display, there should be a standard that you have moving throttles and you don’;t put in FLCH Traps.
You could provide for better commentary if you would read, understand and commit to memory the report on AF447.
one of the biggest issues I have is in normal mode you pull back to escape and rely on envelope protection, or you push forward to command a recovery from slow speed if not in normal mode,
same flight condition, opposite flight control command based on flight control law.
mode awareness is a big deal!
“ conventional stall is only possible in alternate and direct control laws, because of the protections provided in normal law. Alternate or direct law will be indicated by ECAM and the changes on the PFD ; bank angle and pitch limitation replaced by amber X, low speed indications change from alpha prot. to VSW. VSW is load factor dependant and will increase with increase in pitch up rate or bank angle.”
the other is coupled sidesticks. i know for coupled columns, there is no hiding a massive pull back.
Afaik: “Dual input, Dual input” voice annunciation.
That is rather difficult to ignore, isn’t it?
The (apparent) Stall Alarm on/off inversion.
that imho is an unpleasant issues.
Its intrinisc logic is OK but it misleads the uninformed.
I don’t respect what airbus did in its primary flight sensors: the triplicated AOA vanes and the triplicated pitot static sensors. Given the number of near misses something more than just more training should’ve been done to an inadequate system. The tendency of the AOA vanes to seize simultaneously could be dealt with by either synthetic air data or the additional redundancy of say a pair of pressure null seeking sensors which have a different failure mode to the vane sensors. (i.e. two vane and two pressure null seeking). The failure of the pitot static sensors is easily dealt with by the use of synthetic air data. Pressure null seeking sensors might also be usable if they can measure an absolute pressure.
what professional value does your respect have?
There is no doubt that Airbus left some big obvious and quite stupid holes in the airbus Fly By Wire system. I have no doubt that EASA and the FAA have a grip on each others reproductive glands.
A/ Only 3 angle of attack vanes. Since the most common failure mode is for the vanes to ice in position more or less simultaneously the two out of three triplication provides no protection, in fact two iced sensors will impeach the good one as has happened on several occasions. The solution would have been to either 1/ install in addition at to the vane sensor different type of sensor, the pressure null seeking sensor, that has a different failure mode, 2 a fourth sensor or 3 synthetic air data that uses the inertial navigation system and GPS to estimate air data and do a plausibility check against the air data.
B/ The lack of additional redundancy for the prandle or pitot-static tubes in the form of synthetic air data or additional sensors. If the sensors fail due to icing they also disable the angle of attack sensors not only disabling normal laws but disorienting the crew.
The fact that to this day Airbus nor EASA haven’t mandated synthetic air data (like Boeing has on the B787) lets me know that Airbus and EASA is captured by the same group think as Boeing was on the B737 and is a tragedy waiting to happen,
“synthetic air data.”
your are falling for the Boeing bullshit bingo words PR game
please provide a comparison of failure modes and expectable MTBF numbers for the existing and your proposed solution.
synthetic computed values are just another “shaved thin for more profits” solution.
i.e. what you do is expand the envelope of systems and interconnections for your failure coverage.
( the automotive industry are still on the verge of failure in their drive towards interconnecting anything with everything. too complex, not KISS at all.)
Uwe, I’m not a fanboy of Boeing. I am not American.
There are as many dead people from Airbuses multiple simultaneous sensor failures (alpha vanes and pitot static tubes) as there are from Boeings MCAS. Media reaction, which is always more anti American, is the difference.
Airbuses makes a fundamental design flaw for fault tolerant and safety critical systems.
Common-cause failure (CCF) means the loss of function to multiple structures, systems, or components due to a shared root cause. The CCF includes those that can result from external environmental effects, design deficiencies, manufacturing errors, maintenance errors, and operator errors.
It’s fair to say that alpha vanes and pitot static tubes freezing simultaneously is a “Common Cause Failure” CCF that defeats redundancy. Sensor diversity is one solution. (pressure null or a different type of sensors)
Therefore, diversity and defence-in-depth has become an important issue to overcome the CCF of the safety I&C systems.
The idea of SADS (Synthetic Air Data System) has been around since the 1980s. The basic idea is to use non air data sensors such as Inertial Measurement Unit (IMU) and GPS fused with vehicle dynamics models to estimate air data triplet airspeed, angle of Attack, and angle of sideslip (either separately or combined). It is not Boeing’s idea.
SADS has gained a lot of renewed interest after the Air France Flight 447 accident in 2009. Several universities and government agencies such as the University of Minnesota, Delft University of Technology, NASA Langley Research Center, and the Institute of Flight Mechanics and Flight Control at Technische Universität München, have been researching the SADS related topics. Recent patents related to SADS have been filed by the leading air data system producers such as Collins Aerospace and Honeywell.
Boeing is to be commended for introducing SADS on the B787. It is more than Airbus has done to deal with this issue.
Be careful you don’t develop the same mentality as a B737 team member in your defence of Airbus.
There must have be nearly half a dozen 2nd generation off the shelf fly by wire systems available for inclusion in a B737 replacement. It was a mature technology, more mature than airbuses.
electrically driven aero surfaces ( old, look at 1930ties Tupolev )
full FBW inclusive envelope protection.
A universal abstract airplane model projected onto real world airframes encapsulated by envelope protections is the prominent and core feature of Airbus FBW.
What Boeing offers is a cancer growth layer cake.
A good start, some editing needed plus removal of hype words
Boeing – and Southwest Airlines – erred in not going with the original 757 configuration (never produced), the shorter -100. SWA did not think long term. (PW might have used it as well, but with a small fleet bet on the widebody 767 and an expectation it could operate into Edmonton Industrial Airport.)
Development of the 757 was interesting, I understand that Boeing dusted off blueprints for the never-built 727-300, then morphed it into a twin with conventional tail, different wing aerodynamics, excellent nose (flight deck quieter, common with 767, less drag).
Did Boeing and customers then miss an opportunity to advance somewhat by introducing the -100 configuration to replace the 737NG?
My understanding is that the UI merge with the 767 was a bit of an afterthought. ( Airbus made commonality a big thing with the FBW types but afair it started smaller with A300 and A310.
When they put a new wing on the NG, was it possible to add longer landing gear at that point?
@Ted, anything was possible but longer gear meant a change in the wingbox (articulating gear wasn’t around then), which mean changing this and that and no longer close to the ground for ground handling, etc.
I understand the whole change in the wingbox thing, but wasn’t the original concept of the 737 being built for Lufthansa, with the stairs built into the aircraft (low to the ground) a factor of jetways not beings around during that period?
Surely, by the time the NG was rolled out, we were all walking down heated (or air conditioned) passageways to line up for packaging into the sardine can?
As far as loading bags goes, all the loaders I worked on had an inclination adjustment switch that allowed the belly boys to get up in there to crink your neck for a good 10 minutes or so.
It’s all about the moolah, methinks. Moving the gear to make more space is a big no-no for the bean counters.
If you fly in Europe you will be amazed how common use of stairs is. Ryan Air is almost all walk across the tarmac and then stairs. But even outside the LLCs at secondary airports, some major airports, Vienna comes to mind, have you deplaning via stairs out on the tarmac and you then get bussed.
Just looking at Vienna now. Looks like they have a mix of jetbridges and buses. Ryanair most likely get the buses.
Very interesting though. Thanks
The reason why Ryanair use stairs is that it allows them a much faster turnaround time (25 mins). Ryanair always uses the front and back doors concurrently, but I’m not aware of (m)any airports that offer dual jetways to service narrowbodies — hence the unavoidable use of stairs. However, this is not a uniquely Ryanair thing: Wizzair (for example) also do it, and they only have (much higher) A320s/A321s — so, instead of using a retractable stairway for the front door, they just use two mobile stairways. It works a treat (at least in temperate climates).
The NG wing inherits the basic structure of the existing 737 wing.
( and thus the real estate for the landing gear. )
Extended and reprofiled to something nearer a supercritical profile.
NASA says it shows “elements of a supercritical design”.
I don’t believe so. The design change would be significant, as it would be also for the MAX. Mentour Pilot has done a video on the 737 gear and why they have remained short. The gear are stowed externally (no doors). The video shows the bay above the gears and the equipment housed there, which operate the wing control surfaces.
Not really externally ( or half submergered like on th DC3).
Just no aerodynamic cover closing over the wheels in the wheel wells.
Not the only type around with this arrangement.
( C-series now A220 too )
Trailing link gear legs aren’t new either.
But the design Boeing choose is not simple at all.
Isnt the core of the 737 landing gear stowage issue shown in photos of the belly in flight….the wheels almost abut each other either side of the keel beam. No room to stow longer ‘legs’
I thought articulating undercarriage was around from the sixties , the Concorde had it too ( and their gear bays met close to centre line as well)
Perhaps a look at history? The Griffon engined Spitfire had a larger propellor that necessitated more ground clearance …
“The designers used a system of levers to shorten the undercarriage legs by about 8 in (20 cm) as they retracted, because the longer legs did not have enough space in which to retract; the levers extended the legs as they came down” – https://en.wikipedia.org/wiki/Supermarine_Spitfire_(Griffon-powered_variants)
I’m sure the engineers at Boeing would have been able to come up with a way to do something like this, possibly the “keep changes to a minimum” mantra precluded raising the fuselage height (for baggage handling for instance).
the -10 solution is rather complex.
It introduces new forces into the gear leg and attachment area.
( like the pivot forces are ~twice the wheel axle loading, a rearward moment is introduced into the gear leg, .. )
It’s nice to see you on Leeham News.
The MAX-10 version doesn’t actually raise the fuselage height when the aircraft is on the ground though does it?
I don’t doubt for a minute that the Boeing engineers could have raised the fuselage with a gear extension solution to put bigger engines more directly under the wings, I’m just speculating that the “don’t change anything that doesn’t absolutely need to be changed” mantra possibly got in the way of some possible technical options.
I understand there would have been additional maintenance, training and operational issues which may also have played into any decision to extend the height of the landing gear.
A lot of conformance to cert requirements hinges on the ground hugging attitude. ( Like no slides for over wing exits. )
The pitch issue on the MAX was related to the engine diameter as much as the engine position. All modern airliners have the engines mounted forward rather than under the wing. The MAX did this to a greater extent than others. But the landing gear redesign wouldn’t have eliminated the need for augmentation, with the LEAP engine.
Think Boeing had a design with the LEAP-1C Engine as well in its computers but eventually dropped it. Most likely with a new main landing gear that expanded further and had some 737-10 features. Somebody in Chicago made the decision to drop it and go for the not as competetive LEAP-1B powered 737MAX
A longer landing would have meant a total redesign of the wing., something avoided for 40 years. The keelbeam is in the way of a “simple” stretch.
I was told firmly that the limiting factor was the wheel bay from the original design. Anything much done to increase the length of the gear would require a big enough redesign of that key part of the wing structure to entail recertification. The cost of that was a firm no-no. From that emerges all the later fiddles.
PS: Not mentioned was the engine fiddle on the first version of the 37 — Fat Albert. A length of “gas pipe” inserted between the hot bits of the JT-8 and the tail pipe-thrust reverser. At the normal length of that combination (DC-9, eg) the efflux would have mashed the bottom of the wing, flaps.
PPS; Maybe to come in later episode(s) is the fact that the 37 program went through three reviews where the question was shall we go on or cancel it. I recall that Condit was in charge of the third one at least and he persuaded the board to continue, with all that we now know.
” Anything much done to increase the length of the gear would require a big enough redesign of that key part of the wing structure to entail recertification.”
Good to know.
The Boeing 737NG had an all new wing.
Its the Wing Box that is the issue.
To be honest, I can’t wrap my head around it all. How wide is the wingbox, is it wider than the wheelspread? I see on the 707, the wheelspread was 22′. Then the 320 got a wing insert, between the wheels and the fuselage. The wheelspread stayed at 22′, but the engines shifted outboard. The 767-400, I assume they had room to move the wheel wells closer to the keel for the extra landing gear length.
If you look at the 737 gear video, or images of the 737 central equipment bay, there isn’t room available. Or anywhere else for the equipment to go. The contained volume is insufficient.
It’s a moot point anyway, since the regulators looked at the MAX engine mounting and found no problem with it.
Boeing has further delayed its 737 Max 10 programme by two years, with deliveries of the largest variant of its re-engined narrowbody now scheduled to begin in 2023.
The company also now expects to deliver the first 737 Max 7 – the smallest of the Max family – in 2021; that milestone was previously anticipated in 2020.”
“…(EASA) says the Max 10 will receive an angle-of-attack (AoA) sensor “integrity enhancement” – essentially a means of reducing the risk from a failure of one of the two AoA sensors. ”
Wondering why this requirements doesn’t originate from the FAA. The 737-10 is important for restoring Boeing position in the NB market, as a A321 alternative.
The answer is simple, the FAA does not care. Their response is the minimal they could get away with after talking to the other AJH’s in the world.
Its their MO but others have failed to realize it goes back to at least DC-10 days.
FAA needs to be torn down and re-built along different lines. Its always going to be internally conflicted and undermined by the standard industry regulatory capture efforts.
All MAX versions should get the safety improvements EASA and Transport Canada asked for. Only MAX-8 and -9 should get it later (but wasn’t it not later then one year?). MAX-7 should have it from the start, but why would the MAX-10 take so much longer.
Money. Boeing is saving money by not doing it for the -10 and retrofit to the others.
Kicking the plane down the runway.
In the meantime they have 450 to deliver and make some money short term.
Frankly I disagree on the need of the AOA. You could get rid of it or the MCAS 2.0 has corrected its issues.
EASA is an EU construct and they wanted to say they did something.
All you have to do is look at EU Covd response to see how dysfunctional the EU is. Far worse than the US despite Trump.
The MAX-10 was expected in about 2 years, by most predictions, so this is a year delay.
The FAA didn’t require the third AoA sensor because, as they found and wrote in their AD summary, it didn’t make a significant difference to safety. EASA wants it as a safety enhancement, for the case of continued precision approach with AoA failure.
It’s not a third AOA.
It’s a safety improvement for the two AOA.
Correct. It’s a measure aimed at dealing with a situation in which both of the original AOAs are defective. This is basic control theory: odd numbers of inputs are preferable because you thus remove the possibility of an even tie. The engineers at Boeing and the FAA need a control theory refresher course.
Now that Boeing *must* implement this on the MAX-10s for use in the EU, they need extra time to figure out what to do. Pathetic.
Alternatively, maybe this is Boeing’s way of letting the -10 die: keep pushing it down the line until it’s forgotten about. Maybe most of the MAX’s ASC606 subtractions are for the -10…who knows? It certainly can’t compete with the A321.
Safety enhancement as described by EASA, and voluntarily accepted by Boeing and FAA, for the case of precision approach. Two AoA sensors are perfectly safe, as certified and evidenced by 300 million hours of operation.
The claim that the delay is caused by the third sensor is speculation. Airlines are also deferring orders. A recent conversion to MAX-10 orders also pushed them out to 2023.
Safety enhancement as mandated by EASA, in redress of archaic practices at Boeing and FAA, to address control theory shortcomings. Two AoA sensors are “not up to modern standards”, as evidenced by an unacceptable number of incidents and crashes.
The claim that the delay is caused by the third sensor is perfectly feasible. Although airlines are also deferring orders, this wouldn’t affect the MAX-10 more than other MAXs.
MAX-7 was being flight tested for certification at the time of the grounding, as the next in line. MAX-10 had not flown yet. Therefore perfectly reasonable that MAX-7 would not be delayed, while the MAX-10 would be.
the issue is picking which vane is bad when they disagree. the third AoA value (calculated from airspeed) is sufficiently accurate to reveal the bad vane and cause it to be failed.
if a vane were failed, but not malfunctioning, there is no problem figuring out what to do.
“Two AoA sensors are perfectly safe, as certified and evidenced by 300 million hours of operation.”
AoA sensor that have no “push through” into flight control are irrelevant as a reference. … and you know that but use it none the less in your train of arguments.
Faults were inconsequential. ( just that taken down refurbisher from the US must have done dozens or more of AoA sensors wrongly configured and released back to end users.
Uwe, the push-through was not the issue, it was the implementation, as discussed here many times and confirmed by the regulators in their approval of the new MCAS.
you are running in circles to do your job.
please stop it.
your argument was that millions of flight hours on NG had proved the AoA sensors to be save.
My counter is that this was never proven as AoA sensor faults had no significant and unavoidable impact on the flight path.
up to the MAX AoA was invariably filtered through the pilots.
[Edited as not germane to the post.]
“.. in which both of the original AOAs are defective”
single fault for:
no quality information, no assured value
quality information ( match, no match ) , no assured value.
quality information ( match 2,3 ), assured value 2:1 voting.
another path is a Kalman style sensor matrix integrating AoA and Inertial, positional information.
This is what Boeing prefers to use.
high complexity, dependence on other subsystems ( and IMHO rasing MTBF concerns.)
Boeing were claiming’ “2020 time frame”in 2018
Yes Grubbie has it right
“The MAX-10 was expected in about 2 years, by most predictions, so this is a year delay.”
The Max 10 plane itself was rolled out of the factory in Nov 2019
It doesnt take 3 years to certify/EIS a derivative from factory rollout
My reference is correct from the time of the EASA announcement that they would require the third AoA, in late 2020. It was expected at that time to be about two years, we discussed that here at length.
As far as the 2018 estimate or rollout, that doesn’t consider the 20-month grounding period, in which nothing could be done, or the current pandemic impact.
if you don’t certify the -10 ( inclusive fixes )
the clock for fixing the other family types
does not start.
Wow…that’s big news regarding the 737-10 (483 orders at present).
Good that EASA put its foot down regarding the third AOA input — but it should have been a re-cert pre-requirement for all models, not just the -10. Dickson should have mandated this as a re-cert requirement: he evidently didn’t devote too much time to the occurrence of a tie in a two-input system. Another reason why the Dem administration should boot him.
Kudos to Mr. Lemme for assembling this cautionary tale.
Hopefully constructive criticism:
The narrative is hard to follow due to the unsignalled jumps from model to model and era to era. An explanation of a Classic design decision jumps directly, without pause or transition, to a discussion of the Max and then backwards to the NG. If I hadn’t been working at Boeing during those times, I wouldn’t have been able to follow the story.
Yes its a great summary bringing together a lot of information, but as you said needs some tweaks and small corrections
Agreed on all aspects.
I had now known the 757 was a 737 replacement nor the negative affects of the aerodynamics by using the 767 nose to fit in the 767 systems.
Flip of that, if you look at a 777, its a 767 nose that they faired the fuselage into a smaller nose as they just copied it. Pretty interesting if you look closely.
The 757 was the replacement for the 727. Its a typo error. The early 737-200 replacement was the re-engined 737-300
In the UK the 757 was to replace the DH Trident, similar to the 727.
Still no Alpha protection. Without it the Miracle on the Hudson would have been the Tragedy on the Hudson.
You can’t make a silk purse from a pig’s ear.
No – but a pig’s ear makes a hell of a chew toy for a dog. My guy won’t even go near a silk purse. I just don’t understand it….:)
Sully actually said the alpha protection limited his actions in the landing. He would have flared & slowed further before impact, if not limited. So this is not a valid conclusion.
That may be what he would have done had the aircraft let him. But that does not mean the outcome would have been better.
He would likely have stalled it dipped a wing and the outcome would have been quite different.
737 has been landed on water, and on a levee, without alpha protection. With a good pilot like Sully, no reason to think it couldn’t be done with an A320.
Thats not the point, we cannot count on having a guy like Sully at the controls. He is one in 20,000.
Compare Sully’s landing to the hijacked Ethiopian 767 landing. It says all.
i think that is terribly unfair comparison. The hijackers had a role in not letting the captain control the airplane unheeded. I think the captain is a hero.
Prior to the crash, Leul had experienced two previous hijackings. The first occurred 12 April 1992 on Flight ETH574, a Boeing 727-260. The flight was diverted to Nairobi after two hijackers with hand grenades entered the cockpit. The second occurred on 17 March 1995, flying a Boeing 737-260. Leul diverted to Sweden when the hijackers entered the cockpit and flew there while holding a hostess hostage. In both cases, the flights landed safely with nobody injured or killed.
Captain Leul Abate (42), an experienced pilot with over 11,500 total flight hours (including 4,067 hours in the Boeing 757/767), was the pilot-in-command.
Leul tried to make an emergency landing at Prince Said Ibrahim International Airport on Grande Comore, but a fight with the hijackers at the last minute caused him to lose his visual point of reference, leaving him unable to locate the airport. While still fighting with the hijackers, he tried to ditch the aircraft in shallow waters 500 yards (460 m; 1,500 ft) off Le Galawa Beach Hotel, near Mitsamiouli at the northern end of Grande Comore island. Leul attempted to land parallel with the waves instead of against the waves in an effort to smooth the landing. Seconds prior to contacting the water the aircraft was banked left some ten degrees; the left engine and wingtip struck the water first. The engine acted as a scoop and struck a coral reef, slowing that side of the aircraft quickly and causing the Boeing 767 to suddenly tilt left. The rest of the aircraft then entered the water unevenly, causing it to break apart. Except for the rear part of the airframe, the broken portions of the fuselage sank rapidly. Many passengers died because they inflated their life jackets in the cabin, causing them to be trapped inside by the rising water.
Leul and Yonas both survived. For his actions, Leul was awarded the Flight Safety Foundation Professionalism in Flight Safety Award. (1997)
Yes, although the outcome was tragic, that was an amazing piece of flying by a valiant crew.
The first officer fought his way back into the cockpit to defend the captain, who was trying to ditch the plane, while being assaulted and with the hijackers grabbing the wheel & throttle. If he dipped a wing, that would be in no way surprising, under the circumstances.
No real comparison to Sully at all, and nothing to do with alpha floor protection.
If a Miracle on the Hudson event happens to the new version of the 737-MAX, and one of the birds takes out an AOA sensor, that would add to the Pilot workload, for just the added alarms buzzing and lights flashing. On the Airbus, they have more than just two AOA’s and flight control computers. How you ‘vote’ with just two computers, or just two AOA sensors on the 737-MAX, still baffles me.
all Boeing airplanes only have two vanes.
their purpose is usually applied to trigger stall warning and to determine a minimum operating speed.
they also are used to correct the static port pressure reading to enable reduced vertical separation minimum.
a single vane failure triggers the following major events at the same time
False Stall Warning
Misleading minimum speed display
Misleading pitch limit indicator
the false stall waning triggers stick shaker and elevator feel shift, making it hard to pull the nose up.
automatic pilot/throttle drop off, unavailable.
For Airbus, keep in mind that envelope protection takes the vanes reading over the pilot input, and a plane crashed when two vanes froze up and the pilot couldn’t stop the descent.
Maybe they should keep the AOA vanes inside, so they don’t freeze up (grin)? Actually, I think they do have some aircraft that use synthetic AOA, using 3-D accelerometers to help break a tie?
Military fighter aircraft use a pressure null seeking sensor. They are smaller, more robust and have less drag. They can also self test since the motor that nulls the pressure can be checked for rotation. A combination of vane and pressure null seeking sensors should have been used to cross check each other.
They should have just let that 737 go and built the 757-100 and then had the 200 to the spec that was required. Obviously, they were more obsessed with the 767
Regarding the Leap engine, “The first engine entering the test program reached and sustained 33,000 lbf (150 kN) of thrust, required to satisfy the highest rating for the Airbus A321neo.”
If the 737-100 was designed as a low standing aircraft, and the geometry of the wing and landing gear went unchanged, maybe the fundamental flaw was making it into something it could never be. Was MAX optimized for the 7/8? Was the engine optimal for the 7/8 and a replacement for WN of the 737-700 mission?
Was there a potential for a lighter engine, with smaller diameter core, that could have improved efficiency over the CFM-7? Without the drawbacks of the weight and larger area causing MCAS?
Is the leap 1B core smaller diameter and much lighter than the 1A core? If not, the A321 needs were a Albatross hung on the needs to replace a 737-700.
You really are mixing a lot of stuff up.
The Leap for the MAX and the LEAP for the A320 series NEO are NOT the same engine.
Equally having a common engine for the A320 series and another common one for the MAX series is huge in cost control as a boutique engine for each model would be beyond anyone’s means to make cost efficinely.
Ask RR and Airbus and customers about the much different A350-1000 engine vs the A350-900. And that is on a lower numbers of wide body that is easier managed.
You are correct that the Leap A and Leap B engines have little in common
“the much different A350-1000 engine vs the A350-900”
No its not, but whats the difference in stages, pressure ratios etc to prove your claim, yes its more thrust but thats a common step change in this engine series.
‘6-stage turbine, an 8-stage IP compressor is powered by a 2-stage turbine and a 6-stage HP compressor is turned by a single stage turbine, rotating in the opposite direction of the two others.’
If you want to see a significantly different engine look at the GE90 specs for the 777-300ER over the earlier 777 models.
Fan size 123in to 128 in
Compressor 1 fan, 3-stage LP, 10-stage HP to 1 fan, 4-stage LP, 9-stage HP
the weight jumped from 7.7 t to 8.7 t
Bypass ratio increased , pressure ratio increased as well.
All these significant changes pushed its sole user the 777-300ER to its class leading performance which had been maintained up till its replacement by the GE9X
The Trent XWB for the A350K has its basic parameters the same as the smaller cousin, no date theres some internal changes
I suppose the re-engine versus new aircraft also depends on perspective if this was the definitive twenty year solution. Another way of looking at it is that the 737 re-engine could have been a five or ten year stop gap, with a new small aircraft launched in 2016 or 2021. That would have had the advantage of giving them some dynamic pricing power, as Airbus has with the A339neo and A359, when there is some product overlap.
Wing box! Thanks for the precise correction … should have exercised memory cells a bit more before hitting send. Howard
A different perspective on the 757 as an airplane that should have replaced the original 737:
The 757 was designed as a replacement for the 727, not the 737. Early 757 design proposals kept the 727 T-tail but shifted the engines to the wings.
Within the company, at the time of 757 EIS, the 737 was viewed as a niche-market airplane, for short trips from small airports. In the early 80’s the “Classic” was supposed to be a stopgap airplane to extend the 737’s lifetime while customers waited for the 7J7, the new 150-seat design that was supposed to enter service in the late 1980’s to compete with the A320. The 7J7 never happened, in part because customers fell in love with the 737-300/400/500.
I had to laugh when I saw the comment that the 767 got all the money and that the 757 development was short-changed. From my perspective at the time, Boeing management was very much focused in Renton where the narrowbody 737 and 757 were built. The widebody 767 and 747 were built in Everett. Anything north of I-90 was considered a backwater off-site location.
Seems hard to confirm that 767 ‘got all development money’ when the 757 was ‘all new’ except for the upper fuselage lobe carried through from 707 to 727 to 737 to 757.
Hi Pete, great comments! If the 757 had been a direct replacement it would have had a chance to meet the new market that the 737-400 gathered. It is funny that I never viewed the 7J7 with much enthusiasm in my time there. I did have a chance to chat with Dale Ranz who referred to it as the flying cuisinart. The noise. The 7J7 was overloaded with technology – the 777 really got it right, would have been interesting to see how it would’ve ended up – they were thinking about sidestick. I was supporting 757/767 Thrust Management in the day, worked in Renton at the DA/FCL for Everett management. 757 is a hell of an airplane, but the 747-400 is even more. And the 777 came out really nice. BTW, Alan Mulally was 7J7 head.
I missed the mentioning of Lufthansa, Avianca and Malaysia–Singapore Airlines as commercial launch costumer for the 737-100 Jurassic.
Hi, I did too! Thanks for the reminder.
IMU the 737-100 was the product of LH’s wishlist handed in at Boeing.
No where have I found, in an extensive literature review on this subject, any mention of 737 MAX Program Risk Management, Boeing Commercial Aircraft, or Boeing Corporate Enterprise Risk Management. Am I missing something?
This is an excellent article by Peter Lemme. The technical failures of the MAX MCAS system are now understood as are the commercial pressures and historical process.
What we now need to understand are the psychological aspects to this: the group think, the way some characters “got on board” with the program. How others are suppressed. Control engineers from outside aviation would immediately have seen the flaw in MCAS relying on 2 sensors.
A shrink never works–A318, 737-600. Years ago, one of the configurators said that the best shrink of the 757-200 to meet a 160 seat requirement would be to not change anything and only take out a few rows of seats.
Peter Lemke has a number of oversights here. First, the 757-200 was developed when the airlines were regulated. The high frequency and hub-and-spoke business models had not been developed. So to criticize that the airplane is too big is Monday-morning quarter-backing. This was an airplane with transcontinental range to replace the 727s.
There is also no discussion about Delta’s RFP for a 160-seat airplane to fill the gap below the 757, which led to the 7J7 program. Remember that the in the 1970s there was technological focus on fuel economy, which was why the open-rotor design was being pursued.
As I remember that time, the success of the 737-300 was to a large degree a surprise as it benefited from the hub-and-spoke business model after deregulation. Southwest ordered it for their point-to-point network, but other airlines used it as hub-and-spoke took hold. Again, it would be Monday morning quarterbacking to hold Boeing configurators and managers accountable for anticipating this innovation. It was said about the 737 program that management made decisions assuming that they were never going to make another one.
The 737NG was launched after Boeing lost a campaign which pitted the 737-400 against the A320 to United Airlines. “Why would I buy an airplane that flies slower, doesn’t fly as high, and takes longer to climb to altitude?”
I believe Southwest Airlines had roughly 1 out of every 8 737s at the time, fleet size was 258 at first 737-700 delivery. They were also the only airlines making money when the 737NG was developed. Southwest was going to get the airplane that it wanted. The rumor was that Herb Kelleher said he didn’t need the trans-continental range of the 737NG but that he wanted the other guys to know that he had it.
Hi Jeff, I really appreciate your comments! I wonder how a smaller 757 might have fared in that competition with the A320. I can tell you with absolute confidence that Airbus price could not be matched. In any case, the deregulation was a factor that changed the market and I am glad you brought it up. Who knows how the 7J7 would have ended up, but it sure was setting up to be a spectacular new airplane. The UDF was, for once, only a part of the story. I never took it that seriously, in the day, was too busy focused on 747-400 I guess. I will cover this better next time around. Thanks.
I don’t disagree with your premise that Boeing made a strategic mistake when it chose to forego development of a new airplane when it launched the 737NG. The late response to the market and the high development cost of the 777 likely made it difficult for corporate to accept a longer and most costly development program. It is fair to say that once an airline orders an airplane that it is highly likely that additional orders would be forthcoming. Another year delay in schedule could have dug a pretty big hole for marketing. I’d guess that the United commitment to the A320 following Northwest’s early acquisition made it more acceptable for airlines to consider the A320. For example, USAir ordered the A320 in 1996.
The 737-400 was Boeing’s attempt to fill the need for an 150-seat (2 class) type airplane, and that worked for Southwest Airlines and for awhile with Piedmont/US Airways. But is it a less capable airplane and really can’t compete head-to-head. It’s advantage is that both airlines already had 737s in the fleet.
As to your question about whether a new airplane could have competed with the A320, the answer is a bit yes and no. With a common-type rating between 757 and 767, one is committed to exactly the same cost structure–same APU, same flight deck, same engine technology. The only way that the cost comes down is through volume which spreads out the development costs. Two engine types–Rolls and Pratt–works against lower unit costs. And then the question becomes can a new Boeing product provide sufficient performance benefit over the A320 to justify a premium on price? Not likely considering that both would have same technology and target the same market segment. Maximizing flight deck commonality with 757/767 would be an advantage for some operators.
It needs to be said that Southwest was very price conscious and likely any business case for a new airplane would have needed a substantial Southwest order. I’ll remind everyone again that in the 1980s and 1990s Southwest did not consider the other mainlines as their main competitor. Its main competitor was the automobile and customers were very price conscious. I don’t know the details but supposedly SWA would not order many autopilot/flight management options to keep the price down because it stage lengths were so short and much of the flight was hand-flying anyway.
Thinking this through a bit. I suppose Boeing could have launched a new 757/767 technology airplane in the mid to late 1980s, but then CATIA wasn’t quite ready yet. And it doesn’t seem to me that the engine technology had advanced to justify anything better than what CFM was already providing on the 737-300. I can see why the business case just couldn’t close.
Need to make an important correction here. Southwest did not operate the 737-400. Alaska and British were two of the more significant 737-400 customers.
“A shrink never works” Almost never I guess. A330-200, EIS 1998 quickly sold more than 600, for opening new routes to/from booming Asia. Pushed the 7e7.
Shrinks are kinda funny – they are not the optimal version of a particular model, usually being over engineered and too heavy with many components common to a bigger sibling, but there is more then just that.
For example, what if an airline(s) really need a particular aircraft in a particular niche and that shrink is the only game in town? Whaddya do?
What if you are married to a particular manufacturer and need an aircraft that is a shrink? LUV and the 737 Max 7 come to mind;
Southwest and Boeing have a storied history together. Urban legends are told about the handshake agreements that were made to secure aircraft. Now because of the grounding, LUV was said to be looking at other options – notably the A220.
There is no doubt that the A220-300 would be a better aircraft when put up against the Max 7 for the job that needs to be done. BUT, for a bunch of reasons, LUV will buy the Max 7 and stay an all BA carrier;
1) That will get a great deal. BA went down to $33 million on the Max 7 to Delta when bidding against the A220. LUV will get theirs cheaper
2) Commonality. All LUV pilots only have to be 737 certified. They will only need 737 sim training (more about that later). Maintenance is only for the 737.
3) Straight cash, Homie. In a previous 10Q filing, LUV revealed that they got some $420 million from BA in compensation. Apparently they also get the cheapest price in the US on a 737 AND they get a $1 million discount per aircraft if sim training is needed. A million here and a million there, pretty soon we’re talking about some real money.
4) Free planes. In it’s most recent filing LUV stated they expected to take 35 Max’s over 2020/21 AND they were not going to pay Boeing any more money for them.
Now, the Max 7 may not fit their needs as well as an A220 might – but when you get treated this well…it’s kinda like an offer you can’t refuse.
Apparently there are a grand total of 52 orders for the Max 7, as of today. When LUV puts pen to paper, it’ll jump by some 300 units…
Aside from delivering the Max 7 already built, underselling would appear to be sunk cost fallacy.
I don’t see the logic in Boeing’s pricing. 100m for a -7, 120 for a -8. 20% more for something with 17% more seats, that in reality costs probably 5% more to build at most.
I wonder what the actual pricing differential they are offering WN looks like between the -7 and -8?
List prices look good – probably best to the uninformed investor.
LUV is getting their Max 8’s at ~$37 million a copy. I can prove this from their 3rdQ/2020 – 10Q filing, in which they sold 10 Max’s in a sale leaseback deal for $410 million and had to recognise a $70 million gain.
From what I have read, BA offered Delta the Max 7 @ $33 million, so you know LUV is going to be under this.
Probably about a $4-5 million difference.
Market value for a Max? Maybe $40-45 million, depending on the bells and whistles (and the all important “So, how many do ya wanna take?”)
Throwing good money after bad?
In today’s market, which is totally wacko, mostly to the money printer going brrrrrrrrrr – it seems to not matter.
BA could announce to the world that they are selling 300 Max 7’s to the world, with a list price value of…..$30 BILLION!
Boom goes the stock, the crowd goes wild, the game has been won, everyone makes out like bandits (except the shorts), execs cash in their options, everyone get’s an “Atta Boy!”
Doesn’t matter if they sold them at $25 million a copy and will lose $3 million each (random low price and loss number). 300 aircraft will probably take some 5 years to deliver and by then, well – there’ll probably be some other guy sitting in the hot seat(s) trying to figure out how to kick the can down the road, so he or she, can get paid.
Watch – it’ll happen. The Max’s sold to LUV will have very little margin and shares will skyrocket.
WN, SWA, LUV…it’s all so confusing!!!
A318 was a band aid. IMU done after the small NB coop project AE 316, AE317 foundered.
It is lighter than a plain shrink. ( A318 introduced weldattached stringers for the fuselage. .. )
excellent piece by Peter Lemme.
One issue I would like t know more about: I thought the 757 cost so much more to build in comparison to a 737. So, how could the 757 then have competed against the A320?
757 and A320ceo are far apart, much more MTOW, OEW, pax.
The 97t 321LR could beat the 757-200 in range few years ago.
My experience is limited to turbojets, military hands on flying So I will plead ignorance of a lot of automation system knowledge and understanding.. But I will harkin back to Some age-old concepts I learned years ago Engineering wise you don’t over complicate an already complicated system. And you don’t fly trim. I will never bored one of these over complicated rushed through designs.
This is a very well done commentary on the 737 – thank you for providing this.
As I read the history of this aircraft I could not help but think of the shift we as a society have made during the life of this aircraft.
The role of the company has always been to make a profit but the focus on shareholder return and the shift towards self regulation certainly contributed to where we find ourselves.
Independent oversight is sometimes necessary – different perspectives will often surface issues not obvious to those in the trenches
The 757 is a beautiful design, no doubt. But at the time it came out, it was who cares, another single aisle stuffed with more people than a 727-200, the cattle car of the day. The change from a 707 or DC-8 to the 747, DC-10, and L-1011 was dramatic. The tyranny of the tube had changed to spacious room-like zones.
Hopefully Boeing will see the light, and go twin aisle in the 752/753 capacity. Otherwise, another uninspired who cares moment in the evolution of passenger travel.
Thanks for this interesting article. I noticed that the body width of the 737 is exactly the same as it was already for the 707 – in other words the basic body tube has never been changed. The obvious question I have now is whether the seize (and may be the engineering) of the windows was ever changed.
“in other words the basic body tube has never been changed. ”
Not quite , the tube has upper and lower sections – and they are built separately. The upper tube hasnt changed but the lower lobe has through the different iterations.
A graphical representation of the early Boeing jets sees the 367-80 at 132 in width, the KC-135 grew to 144in , the 707 became 148 in. The vertical dimension changed also along with floor location. The DC8 by comparison was 1 in less width but a deeper underfloor baggage area.
image from ‘Evolvability and design reuse in civil jet transport aircraft’