Is the Boeing 737MAX Really Unstable?! The 737 Engine Saga.

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Using a single sensor for MCAS even though two were available and it really should have been three was criminally stupid. And not mentioning MCAS to the pilots seems actually criminal to me. Why was nobody sentenced to prison?

Imagine an alternate world where Boeing didn't merge with Mcdonald Douglas. And instead just made a successor to 737 in 90s.

RIP John Barnett, you will be remembered for standing up for what's right...

You should drop BetterHelp as a sponsor as fast as possible

I am a retired aerospace engineer and a sport pilot. Your videos provide the absolute best explanations of these issues. Thank you so much for making them.

You are absolutely right when you say that using heavier engines or moving the engines forward increases static longitudinal stability, but may create longitudinal controlability problems. However, the main problem with the 73 max is an inversion of the static longiitudinal stability at high angles of attack, probably caused by altered airflow patterns aft of the engines toward the horizontal tail. It is a solvable broblem. However the way Boeing implemented a solution was a disaster, and we do not understand why the FAA did not catch it: 1) MCAS based on a single alpha vane. An alpha vane has a probability of failure somewhere around 1 failure in 40000h. But the MCAS in a way affects primary flight controls. Failure of primary controls are catastrophic and the requirement is that catastrophic failures can only happen once in 1000000000 hours. (10-9), as per FAA AC 25.1309. Had they used two alpha vanes (deactivating the system if there is a discrepancy between them) the probability of both failing at the same time would be once in 1600000000h, which would meet the safety requirement. 2) The MCAS actuated the stabilizer at a very high speed, turning the stabilizer into a kind of primary control. 3) PIlots were totally unaware of all those differences.

As a control engineer (we are the guys mostly obsessed with stability), I am horrified by how B737 was modified and the control system was augmented. The way this passed regulatory approval is scary. I will never willing fly B737 again.

My understanding is that the simulator test pilot for the max very pointedly made clear that the plane naturally pitches up way more than “slightly”. The MCAS was not there to simply make the plane more pre-Max-like, but to address a serious pitch up issue.

I’ve flown on a 737 with gravel kit. Canadian North retired them only after the pandemic. Air Inuit still has one.

Not exactly to keep regulators happy, was it... it was to persuade regulators to keep the same type rating so that airlines didn't have to do more pilot training. Or am I wrong?

Your callout to Stefan Drury's channel & encouragement to help him out: that was kind & generous. Thank you for being a friend to him. That small gesture is infectious - encourages community amongst us all, is an example of how we can all help each other. We need more of that. I've occasionally enjoyed your channel's posts, but am now subscribed to yours & his.

If it’s a Boeing I ain’t going.

I never knew they extended the gear length. Every other source concentrated only on engine placement. Thank you.

Together with Jean-Claude Malroux of Snecma, my father was part of the original marketing team for the CFM-56. The big break was the DC-8, which was an obvious easy re-engine, followed by the KC-135 and other 707 military variants. My father always felt that the 737 re-engine program was a rush job as Boeing tried to keep small Airbus variants from eating their lunch. Still, the 737-300 broke the Pratt stranglehold with Boeing and proved to be a launching point for both CFM and GE. That clever engineering you mentioned paid off hugely. Although long-retired by the time that the MAX line came out, Dad was still connected enough to know that one of Boeing’s major pitches for the LEAP-engined planes was to that they were to require minimum pilot retraining. And therein lies the rub and at least some of the design errors.

I never finish a full video on YouTube or never watch a full tv show or movie. However with your videos I have never stopped it early and always watch it in its entirety. Thank you for the awesome consistent content.

I'm a private pilot, (love the decathlon for the upside down silly stuff), and obviously never flown the big guys but I love hearing the technical stuff about how these huge metal boxes fly.

You are correct regarding the reuction of the fan diameter on the CFM-56 engines powering the 737NG, but your explanation was incomplete. In addition to lowering its efficiency, this lowered its power too. The engine was derated from 24,000 lb of thrust to 20,000 of thrust. Also, your explanation of the MCAS is great. I would like to add that MCAS is not new to the 737MAX. An MCAS was implemented on the KC-46 (767) air refueling tanker. This much more robust MCAS was needed because a tanker's center of gravity is frequently changing during flight as the tanker offloads fuel to recipient jets requiring it, and as such, MCAS is more active on the refueling tanker. The KC-135 tanker and KC-10 Extender tanker had a Second Officer (flight engineer) who was in charge of fuel transfers between tanks (to manage the center of gravity) but the 767 tanker does not, and requires more robust computer functions to fly safely. The 737's MCAS was less robust, lacking sensor redundancy, to reduce its cost, because Boeing calculated that airline 737s would not need it often, only in specific situations. Boeing's assumption, while correct, led to a problem which not only caused two crashes, but also caused some incidents on US airlines that could have resulted in crashes, but did not.

High, I’m a 737 veteran myself and quite familiar with the concept you are discussing. I flew most variants of the 73 and my flying came to a halt when the mcas mess came about a few years ago. I was in the middle of the type conversion in Singapore when it all happened. Anyways to the point, I firmly believe that it’s time for Boeing to say good bye to the 73 and maybe concentrate on the 75 comeback and making that model a better unit than the original was. I’m not an engineer but common sense tells us that shrinking an airframe is probably a little easier than trying to stretch it as in the max. The Russians have come up with an airframe around 210 pax and I think that’s a good size to have, which is why I think a redesign 75 makes a lot of sense. And knowing Boeing will do anything to screw this up, make it a totally new wing design instead of the bs job they did with the max which was the same airframe as the NG. A new design is a new aeroplane period.

I haven't watched your main channel in years. This channel of yours has been really successful & amazing in terms of education. Your like my Aviation pilot teacher.