Leeham News and Analysis
There's more to real news than a news release.
Leeham News and Analysis
- Bjorn’s Corner: New engine development. Part 4. Propulsive efficiency April 19, 2024
- Boeing unlikely to meet FAA’s 90-day deadline for new safety program April 18, 2024
- Focus on quality not slowing innovation, says GKN April 18, 2024
- Boeing defends 787, 777 against whistleblower charges April 17, 2024
- Dissecting Boeing CEO’s statement next new airplane will cost $50bn April 15, 2024
Fly By Wire: US Airways 1549
We’ve just finished reading “Fly By Wire: The Geese, the Glide, the Miracle on the Hudson,” by William Langewiesche.
It’s about US Airways 1549, the Airbus A320 pilot by Chelsey Sullenberger and Jeffrey Skiles, forced to make an emergency landing in New York City’s Hudson River last January 15.
We’ve also been reading the reviews and reaction to the book, including Sullenberger’s reaction. We wonder if we’ve been reading the same book as the critics, who dispute the contribution the A320’s fly-by-wire system made to the safe landing.
To read the critics’ response, including Sullenberger, one would think Langwieche gave all the credit to the A320 for the safe landing and none to the flight crew. Nothing could be further from the truth.
Langewiesche gives full credit to the skills of Sulley and Skiles for their actions in the short, 3 1/2 minutes from impact with the geese to landing in the water. He is generous with his superlatives in describing Sullenberger’s skill, calm and split-second decision-making.
The point of his book is to examine the fly-by-wire design of the A320 (and subsequent Airbus airplanes) and discuss how, in this case, the system contributed to the safe landing. His is not an either-or proposition; it’s an “and.”
Sullenberger rather grumpily responds that he would have made a safe landing in a conventional Boeing 737 that doesn’t have fly-by-wire. Whether he would have or not will always be a matter of conjecture. One can only wonder what might have happened to United Airlines Flight 232, the DC-10 that crash-landed at Sioux City, Iowa, despite the superb skill of the cockpit crew had the DC-10 had fly-by-wire to help stabilize the airplane.
Langewiesche details Sullenberger’s quick decisions made under high stress. While Skiles was occupied trying to restart the two engines, Sullenberger had to evaluate glide ratios, heights, distances and immediately conclude he didn’t have enough altitude to get back to LaGuardia Airport. Sullenberger immediately decided to turn on the APU, even though this is not part of the engine-out procedures. The APU permitted generators to work after No. 2 engine completely failed on its own and after Skiles shut down No. 1 (part of the procedure) in a last-ditch effort to restart the engine, less than a minute before impact.
In effect, the fly-by-wire acted as the third pilot, enabling Sullenberger to fly to a successful landing. The plane couldn’t have landed safely without Sullenberger and Skiles at the controls. Whether Sullenberger could have safely landed the airplane without the fly-by-wire may be answered when the NTSB issues its report. But it seems clear he was helped.
The book is not without its flaws. It becomes tedious in spots as Landewiesche seems to be including stuff more to fill space than add to the story–a routine set of exchanges between a controller and a series of flights takes up the better part of two pages. And, like Langewiesche’s excerpt earlier this year in Vanity Fair, he takes forever to get to the point. We skipped over many, many pages because we were bored (exacerbated by the fact we had read the Vanity Fair piece when it came out and were equally bored then). But once he got to the point of 1549 itself, we found the interaction between Sullenberger, Skiles and the fly-by-wire quite interesting.
Why people are reacting as they are is a mystery. Langewieche takes nothing away from the pilots in writing his book.
Thank you for not using the word “miracle” in your review of Landewiesche’s book. IMHO, that word has been inappropriately used in all of the videos, books, and articles about flight 1549. A miracle implies divine intervention. What we had here was well-trained flight and cabin crews doing what were supposed to do in a well-designed and well-built airplane that is expected to hold together in all but the most violent situations. No miracle required.
Or “hero.” Sullenberger, Skiles and the cabin crew did their jobs. “Heroes” in our book are those who put their lives on the lines for someone else when they don’t have to.
The reason people have reacted to the book negatively is because of the way the book was promoted. They probably haven’t read it. The publishers knew that if they didn’t seek out some controversy, the book was going to get no press and would languish on the shelves. Instead they push the “pilot was an accessory” line, even though they know the book doesn’t make that argument. And what happens? People attack the book on the internet, then people defend the book on the internet, then people buy more books. It’s all marketing.
Another mystification of ‘Fly by Wire’.
This term simply means that every actuator and
sensor of an aircraft is driven locally by means
of electrical motors or hydraulic pressure, while all those devices are also hooked up via signalling networks to the bord computers, where the steering is centralised.
This is an additional abstraction layer, which was not available in earlier aircraft designs. It allows for much more steering flexibility and faster reaction time. But the primary benefit of the ‘Fly by Wire’ concept are the huge weight savings, as there is no centralised hydraulic system and electrical grid anymore. Everything is hooked up on single supply busses which run throughout the aircraft. Access of every device to the supply bus is controlled with digital steering signals over the wire. Also feedback from the sensors is received over the wire.
By the way, also the ‘Fly by Wire’ concept is outdated now. For example the Airbus A350 XWB will already follow the ‘Fly by Light’ concept.
This allows for further weight savings and much higher data transmission speed, as the connections consist only of very thin and light weight glas fibres.
Actually, “Fly-by-Wire” itself does not necessarily change the handling of the aircraft. The unique thing about the Airbus A320 and later are the flight control laws, which significantly change handling, for example by interpreting pilot’s pitch input as vertical load factor command instead of a proportional elevator deflection command. The Airbus approach is different from that Boeing used on the B777. In the end, both systems have their ups and downs, and you rarely hear pilot’s complain about the good-ol’ B737 “Fly-by-Cable” flight controls.
Although I haven’t read the book, I would doubt that the Airbus flight control laws played such a major role in that accident.
If United 232 was equipped with a fly by wire system like an A320, it would have almost definitely crashed totally uncontrolled and all aboard would have died. United 232 lost all hydraulic power when all three hydraulic systems lost fluid. The crew was able to move the flight controls manually (with great effort) due to the physical connection of a conventional flight control system. Neither they nor the computer would have had any control with fly-by-wire. Had the APU failed to start on US 1549, the same result would have occurred.
Airbus FBW shifts to Alternate Law to permit throttle controls in such a situation.
If the APU had failed on US1549, the RAT would have deployed (as it did on 787 ZA002) for alternative power.
You are correct. The misinformation about the APU saving the day is just wrong. The 320 would have already gone into ALT2 when the engines lost power and stopped data from the air data ref units. The power source for the computers has nothing to do with which law the 320 operates in.