Bjorn’s Corner: The challenges of airliner development. Part 9. Size of the airliner.

By Bjorn Fehrm, Henry Tam, and Andrew Telesca

June 25, 2021, ©. Leeham News: We are closing in on our aircraft project, where we will go through an aircraft development from A to Z and look at how certification rules govern our work.

Before we decide what aircraft to develop, let’s look at how the certification rules break the market into segments based on cabin seating.

Figure 1. An example of a 50 seat airliner, the ATR 42. Source: Wikipedia.

Breakpoints in the airliner market decided by certification rules

In previous parts of the series (Part 5 and 6), we saw that the Safety certification rules for the aircraft and the Operating rules for the airline combined to divide the market in two segments:

  • Propeller aircraft with nine seats or less, governed by 14 CFR Part 23 Normal Category Aircraft rules and operational rules under Part 135 Commuter and On-demand Operations.
  • Propeller or Jet aircraft with 19 seats or less, certified to Part 25 Transport Category Aircraft and operating under Part 121 Regularly Scheduled Air Carriers.

Equipment and proof of safety vary for these aircraft, but these classes do not require a crew above the two pilots. Is there an additional category of aircraft above Normal and Transport Category aircraft? No, there isn’t.

This means there isn’t anything in rules that makes certifying a 51-seat aircraft more complex than a 50-seat or larger aircraft, as we stay in 14 CFR Part 25 for aircraft certification, from 20 seats and up.

There are other reasons there is a segment break for airliners at 50 seats.

Under FAA Part 121 or EASA Part-CAT, one flight attendant is required when the seating capacity exceeds 19.  An additional flight attendant is needed when the seating capacity exceeds 50.

The marginal revenue from a few extra passengers above 50 does not justify the extra crew member cost. Keep in mind; it’s not only the personnel costs that increase; the aircraft OEM must install an additional cabin attendant seat and associated equipment on the aircraft as well.  The 50-seat configuration, as a result, makes more economic sense if our routes have around 50 passengers per departure.

US-specific segmentation

In the United States, so-called Scope Clauses between the mainline Pilots and their Carrier constrain the size and the number of regional aircraft the Carrier can outsource regional traffic to.

Here the negotiated size brackets are 50, 70, and 76 seats with a specified Maximum TakeIOff Weight (MTOW) per category (an indirect way to restrict the length of routes the aircraft can fly).

The different size brackets have limitations on how many aircraft each bucket can have. The 50-seat category is generally the least restrictive in terms of fleet size. Therefore, in the US outsourced market (80%-90% of the US regional aircraft market), having 51 passenger seats pushes the product into a larger Scope category, which is more restrictive in terms of fleet size, on top of requiring an extra cabin attendant.

The end result is size segments for the US market of 9, 19, 50, 70, and 76 seats. Above these, aircraft are no longer operating under Scope agreements, and the next natural limit is 100 seats, above which three flight attendants are required. At 150+, this changes to four, etc.

International markets

The limits of 50, 100, 150, 200, etc., are relevant in the markets outside the US, with the requirement for an additional flight attendant when passing these seat limits.

As the costs for an extra cabin attendant become less troublesome as the seating passes 100, the market segmentation around these limits is less pronounced once above 100 seats.

23 Comments on “Bjorn’s Corner: The challenges of airliner development. Part 9. Size of the airliner.

  1. I will posit that there is a traditional constraint on aircraft size. It is the size of the door. The legacy of door size has created the challenge of how the aircraft itself interfaces into infrastructure. We essentially have 3 sizes: small (ATR/DH8) – not jetbridge compatible medium (73X/A32X) and large (350/787). Changing this has been the challenge of every new design. Now we have more radical designs required to break the 25%+improvement barrier, this issue has to be part of the new design consideration.

    • “.. not jetbridge compatible medium (73X/A32X) ”

      In Heathrow you board BA A319 via jetbridge.
      Same for Hamburg Helmut Schmidt airport.

      RY loves non jetbridge ops because it is cheaper.
      .. or just because there are none on the premises ..
      Like their destination “Hamburg” ( which actually was
      the Lübeck- Blankensee smallish rural airport 50km away )

    • Even ATRs Dock with jetbridges. I was surprised coming out of an American Eagle ATR42 in LAN, but they do. 737s/A32s do it all the time.

  2. We may be heading to a situation where for a 150 passenger aircraft the rules may allow a single pilot but require 4 flight attendants?

    • The flight attendant numbers are there to help with evacuation, and whats wrong with having cabin service ? In practice an airline will do what Southwest does , have just under 150 seats to have the 3 attendants ( as per the Max 7)

      • It’s a statistical process I suppose. Will having one pilot less cost more lives than a partially botched evacuation from having one less flight attendant less instead. Targeting the pilot seems to be driven by wage differentials rather than safety concerns.

        It would probably be possible to have an tracked, automatic 20cm narrow service trolley delivering small meals but would require the cooperation of the aisle passengers. Low Cost Carriers have achieved wonderful things for those of us able to travel light.

        • I think another way to look at pilots is not the cost, its availability.

          The CEO of American was recently complaining the military was not supplying them enough pilots!

          Rather than build their own pipelines, the airlines depended on military for those who wanted to keep flying (in the officer driven US military, you get promoted or you get booted out). Many don’t want to be a Colonel, they like to fly.

          Back in the 1950 era they paid people to go to the ATR conversion schools.

          To get both the training and flying time (1500 hours) you spend huge amounts ($150,000) can be washed out, and miserable methods to build hours.

          Now the so called Aviation romance is no more, basically a pilot is a bus driver (sans a Sullie both engine out ditching (and yes he was former military) and it cost you huge to try to get there.

          So now the airlines are getting desperate and some have opened up their own schools and pipelines.

          At some point the tech will be there for a single pilot and something happens the aircraft just auto lands.

          Unless the co pilot is fully up to snuff, they are no help in a crisis as we have seen too often. A good AI assistant would be better.

          • US: dysfunctional lobby-ism and union posturing.

            What a surprise.

          • Lilium Jet, who are pushing pilotless eVTOL as much as realistically possible are estimating it will take 10 years to get to pilotless. The issue I think is air traffic control, something the airframe makers don’t even control. Lilium of course being VTOL and having a ballistics parachute is going to have a lot of options in an emergency. As far as I can see the flight control software and systems on Airbus and Boeing are way to old in ways of thinking. The B787 being better than the Airbus at this time.

            At this point they should get their house in order. Better redundancy, synthetic air data and a system to always find a runway (or pasture, or lake) to glide into on total engine failure.

          • “systems on Airbus and Boeing are way to old in ways of thinking. The B787 being better than the Airbus at this time.”

            statement conjured up from thin air?
            787 seems to be an issue rich blob.

  3. On the subject of “airliner development”, the FAA has issued an interesting statement w.r.t. the certification of the 777X:

    Reuters: “Boeing 777X ‘realistically’ will not win certification approval before mid-2023 — U.S. FAA”

    “The FAA in a May 13 letter to Boeing seen by Reuters cited a number of issues in rejecting a request by the manufacturer to issue a Type Inspection Authorization (TIA) Readiness. “The aircraft is not yet ready for TIA,” the FAA wrote. The letter cites numerous concerns about lack of data and the lack of a preliminary safety assessment for the FAA to review. The letter was reported earlier by the Seattle Times.

    The letter cites a number of issues that still need to be addressed, including an “upcoming major software update with the software load of flight control… The FAA understands that there are many significant problem report items that will be addressed by that version of the software load, including the software fix for the un-commanded pitch event that occurred on December 8, 2020.”

    The agency added that “software load dates are continuously sliding and the FAA needs better visibility into the causes of the delays.”

    It said that “after the un-commanded pitch event, the FAA is yet to see how Boeing fully implements all the corrective actions identified by the root cause investigation.”

    The agency said it wants Boeing to “implement a robust process so similar escape will not happen in the future and this is not a systemic issue.”

    And without paywall:–35726383/

    • A seismic PR disaster for the 777X program, and another high-profile slap in the face for Boeing.
      Nothing has changed at BA…absolutely nothing.

      • BAE is the lead contractor on the complete flight instruments and electronic controls contract including the software. Its not unusual to have incidents during flight testing, thats why its called ‘testing’
        Other problems can arise in a brand new plane as well.
        4 incidents in 3 months ! but its OK as its just unlucky

        In regard to earlier comments about pilots, I thought this was interesting but of course ‘pilots were there but not flying’, under ideal test conditions of course but it runs together some existing auto takeoff and auto land features

        • Sure…aircraft have glitches all the time…just look at the more than 700 Category II deficiencies on the KC-46, not to mention the various Category I deficiencies.

          HOWEVER, when was the last time that we heard a regulator wipe the floor with an OEM in this manner? Particularly with regard to a “flagship” airframe that has been undergoing “testing” now for more than a year?

          “In the May 13-reply, the FAA says it “considers that the aircraft is not yet ready for TIA, even if it is a phased TIA of limited scope with small number of Certification Flight Test Plans proposed. The technical data required for the type certification has not reached a point where it appears the aircraft type design is mature and can be expected to meet the applicable regulations.” Only the first phase of DAR has been completed, but phases 2 and 3 have yet to follow. Without this, the FAA has difficulty determining if the CCS is mature enough. The FAA adds that Boeing and the agency have been discussing TIA criteria for nine months and that DAR dates have continuously slipped.

          Nor has Boeing been able to provide evidence that the 777-9 meets the Preliminary Safety Assessment, which means that Boeing doesn’t meet its own TIA criteria. There is insufficient and inadequate data available to file the Certification Flight Test Plans for this phase of TIA. An assessment of CCS concluded that “data is not yet mature enough to show compliance, lists many open problems against safety documentation, assessments, and requirements”, especially as the GE Aviation system will have a few software updates soon that will address previous shortfalls. It also notes that the analysis included incorrect use of data from the Boeing 787.”

      • There seems to a lot of crocodile tears from the airlines. They might all be complaining about late deliveries but given the COVID-19 situation and their extensive grounded fleets they are all better of accepting these late B-777-X years latter and not paying for them now, while they have minimal revenue, as they would be. It’s their luck. Airbus went through a trauma of delays as well with the A380, supposedly due to the CADIA 5 versus CADIA 4 compatibility issues between France/Germany on the aluminium wiring looms. One good thing is that the4 impending Boeing bailout means that Boeing or the US Trade Dept in charge of such things is maybe getting ready. They are using the need to compete with COMAC 919 as the excuse.

        It would be interesting to see if they can get rid of the US 30% Tariff on EU trucks which is, I believe, imposed on the EU refusal to accept GMO Soy fed chickens.

    • Incredible to read that the 777 had 10 months of flight testing, while the 777X is now heading for 4 years (48 monts). Almost five times as much.
      Most certainly, things have become more complex, and certification might be more thorough, but it might also indicate, that Boeing is just not as prepared anymore and just has a trial and error approach. Let’s do minimal work and see if it runs. Scary…

      • FBW systems have a limitless range of “if then else” type options whereas mechanical systems are simpler since they are physically limited in the complexity achievable. (Kommandogeraet in the BMW 801 excepted).

        I’ve been keeping track of what has been going on a Lilium Jet. After falling short by about $200 on the $500 million capital they needed to raise they have merged with US company QEL investments to get what they need.

        Tom Enders (ex CEO of Airbus) has become Chairman. Honeywell has become an investor and is supplying the flight control system.

        Now I don’t think they needed Honeywell to make Lilium flight control systems work but they probably needed them to certify it given the costs and Honeywell has experience and deep enough pockets to supply in return for a share.

      • Time passed and time spent are two different things.

        .. And the MAX disaster obviously brought a major roll back in the certification effort.

  4. Boeing 777x = new wing, new engines, landing gear, new tail, new cockpit, new fuselage = new aircraft, not a changed product.

    If Boeing had chosen a conservative certification approach instead of an aggressive grandfathering of design and requirements based approach, the would have EIS ~7 years after launch.

    Boeing flet they had congress / FAA in the pocket and could get away certifying the 777x as a 77W derivative to safe costs and time. Congress were no aerospace engineers & loved Boeings funding.

  5. It would seem that the same process of trying to get the 777x certified like the 737Max HAD was flawed. This just shows the extent of BA flawed thinking. A) Trying to copy airbus commonality approach, B) sliding the kitchen sink into every process. There should be a public mocking on the stocks for their behaviour. Calhoun has a huge task ahead. For many aircraft direct purchasers, the old model of “pay as you build” should probably be revisited.

  6. Who believes that the 777X will be certified end of 2023.
    Unbelievable that Calhoun tried to let this aircart get through. Calhoun said he didn’t know about the MAX shananigans, but for sure he knew it for the 777X and he still tried.
    Only fools take Boeing serious. Tim Clark showed that Emirates won’t be one of these fools. Emirates won’t take 777X. Good that Airbus is reducing weight on the A350.
    Who still believes that the MAX is safe.
    Who is not expecting another MAX crash.

    • Well, it’s amazing that the FAA has indicated that it suspects that there may be a “latent failure” in the flight control systems of the MAX — with possible loss of control as a consequence — but that the only proposed remedy is to do periodic checks (during other maintenance). What about a full software audit? Or prolonged failure mode testing in a simulator?
      Where the 777X is concerned, it seems to be taking a much tougher stance. That having been said, with the way BA is dragging its feet it’s a distinct possibility that this plane will never be certified.

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