The Max crux

Boeing, the FAA, and national aviation authorities (NAAs) from several other countries, met in Dallas on 23 May to consider the future of the 737 Max series of aircraft.

It is impossible to overstate how important this meeting is. The way civil aircraft manufacturing does business, not just in America, but all over the world, is under scrutiny.

Detail gradually emerging from Boeing and the FAA following the two 737 Max fatal crashes has upset such basic assumptions about the way modern aviation works that industry veterans – whose initial reaction was that this was just a case of finding a fix and getting the Max airborne again – are , only now, fully realising it’s not.

Like the Looney Tunes cartoon characters who ran over a cliff they didn’t know was there, we didn’t begin to fall until we looked down.

Let’s examine the proposal that all airliners nowadays are massively computerized, so adding some digital controls to the good old 737 to make it a Max is just bringing the 737 marque up to date.

After all, digital controls work on other types like Airbuses and Boeing’s own 777 and 787, and they are safe, so why not on the 737?

Back to basics.

All modern commercial airliners are supposed to be designed, in the first place, so they fly easily and intuitively, and have a natural aerodynamic stability within their flight envelope. That should hold true with or without computer control.

Designing an aircraft to be fly-by-wire, rather than conventionally controlled, can provide additional safeguards, but the airframe itself should still fly naturally.

Applying a digital solution to an airframe-related flight characteristic that is undesirable is a different matter entirely; but that is what Boeing chose to do when it installed the Manoeuvring Characteristics Augmentation System (MCAS) in the new Max.

The fact – revealed by the fatal accidents – that the MCAS could be triggered when it was not needed, and what consequences might follow its triggering, appears not to have been examined in any depth by Boeing or the FAA.

The fundamental questions for the FAA – and the foreign NAAs- are these: is the Max, as a simple airframe without digital corrections, sufficiently stable within its flight envelope to satisfy the regulators it is worthy of certification?

If not, is a digital fix sufficient to cover the undesirable flight characteristics lurking in a corner of its flight envelope? How reliable does the fix have to be to win approval?…and how can its reliability be proven?

For three decades the aviation world has agreed to operate a regime whereby the NAAs in countries where aircraft are manufactured all use the same standards when they certificate a new aircraft. So when the FAA certificated the 737 Max, the rest of the world accepted the FAA’s judgement and did not insist – as in the bad old days of the 1970s and before – on re-certificating it country by country.

What if, in this case, the FAA re-certificates the MCAS-modified Max, but foreign NAAs do not? The European Cockpit Association today has called on the European Union Aviation Safety Agency to scrutinize any FAA approvals, and EASA has pledged to do so. Is this “back to the bad old days”?

At the end of the Dallas meeting Boeing had this to say: “We appreciate the FAA’s leadership…in bringing global regulators together to share information and discuss the safe return to service of the 737 MAX….Once we have addressed the information requests from the FAA, we will be ready to schedule a certification test flight and submit final certification documentation.”

Industry speculation as to when the FAA will be ready to approve return to service varies massively, from a week to many months. These seers also seem to be preparing themselves for disagreement between the FAA and foreign NAAs.

This is the point at which you dare not look down.


8 thoughts on “The Max crux

  1. I almost fully agree. Actually, I raised a good part of the issues in LinkedIn with the exception of FAA accepting a plane that others would reject.

    My doubt is about airframes and FBW. At what extent FBW provides additional protection or it is covering undesirable features of the airframe through MCAS-like systems that could be working even under “direct law”?

    I’m not able to answer that question and I’m not sure the regulators can.

    Perhaps, as you say, these cases are shaking the full statu-quo, especially regarding the relationship regulator-regulated.


    • Jose, I can help a little with what FBW is designed for: provides flight envelope protection. In the Airbus case this, in normal law, means the aircraft will resist pilot attempts to take it outside the flight envelope – like stall, overspeed, overload (excess G) or over-bank. These protections are there NOT because the aircraft’s aerodynamics are faulty, they are intended to protect against error when pilots are overloaded or distracted. Whether you think that philosophy is valid or not is up to you. Boeing FBW does much the same, but pilots can override it.

      As it happens, digital flight control systems are usually cheaper to maintain and troubleshoot, but that’s another issue.


      • Dear David, I saw your program on YouTube on Flight 447. The subject of pilot interaction with the cockpit has been in my radar since early 1990s and applied it to the C-17 aircraft. Please contact me as I feel it is essential to the design and safety of modern aviation. I am a Cranfield graduate.
        Hope to hear from you can reach me by WhatsApp 714 965 0471


  2. Why did Boeing design an airframe with the need for MCAS? Surely they did not. MCAS was the much needed correction in order to fix the pitch problems experienced with the 737 Max. Why did they not design it fail safe?
    But even more shocking – why did Boeing and FAA certify the 737 Max without a fail safe MCAS? There is much needed evaluation and second thoughts that need to answer these questions after two catastrophic accidents with a brand “new” aircraft in 2018.


  3. I am lifelong aviation enthusiast. I have flown models from an early age and graduated to building and flying full size aircraft. I am no expert but one thing I am sure of and that is to design software to cure an aerodynamic design fault cannot be the right way to go. Software to prevent a pilot from placing a correctly designed aircraft beyond its designed parameters is acceptable but not software to rescue a bad design from an undesirable flying condition that was not initiated by deliberate pilot input.


  4. About thirty years ago, there was an article in Flight Internation about the 737-500 (?). In it the author, who was probably you’s truly, talked about the aerodynamics of the 737 and how an unusual fix had been tried.

    I have lost my copy of the magazine, but I would be interested to read it again.


  5. Your metaphor of the Looney Tune character looking down stayed in my head all summer, it really hit the ball. The other day I saw this BBC article:

    When EASA is publicly announcing that they will not accept FAA’s verdict – we are looking down, aren’t we?


  6. Am I reading the situation correctly when I conclude Boeing have certified a flight control system that can fail in a safety critical manner in the event of a single sensor input failure? I thought such systems relied on ‘majority voting’ of at least 3 separate inputs to achieve the necessary safety critical failure rate. Wasn’t the rudder PCU on the 737NG which failed in a hard over condition also the result of a single failure leading to a critical failure mode?


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