Why Boeing 737 Maxs Fall Out Of The Sky – It’s Complicated

That the Boeing 7373 Max plane might not be the safest ever to take to the skies could be truthfully said. Quite why though is the thing under discussion. We’ve had our own attempt at it a couple of days back and it seems that we had the proximate cause right – the software – but not perhaps the ultimate. It’s the series of design choices which led to the plane itself. Which then had to be compensated for by a change to the software.

That, at least, is the crux of this coming explanation. Our earlier one was roughly:

A reasonable – and as yet unproven – theory for the Ethiopian and Lion Airlines crashes of the Boeing 7373 Max aircraft is something wrong with the autopilot or flight control software. The specific point being that to lengthen the aircraft is to change flight characteristics and did the software upgrade change sufficiently to cope with that?

As we say, proximate cause for the Ethiopia and Lion Boeing 737 Max crashes but is it the ultimate one? The best – or at least most interesting – explanation we’ve seen elsewhere being this one:

And on, follow the rest of it here.

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Rhoda Klapp
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Rhoda Klapp

So the software flew the aircraft into the ground and it’s not to blame. Lots of planes get redesigned and extended. The software has a role to play. If it needed recoding and that didn’t happen, then the software flew the plane into the ground. It must have been signed off as safe.

Jonathan Harston
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Jonathan Harston

That’s essentially what I heard on a engineering discussion on the wireless a few days ago. New more efficient engines, needed to be mounted differently, changes whole dynamic of ‘plane, use software to compensate, pilots could stop the software.

Dodgy Geezer
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Dodgy Geezer

The underlying issue is that the plane was not redesigned from the ground up to make it optimally safe. That would cost a lot of money. So they added an extra feature to the control system to make it safer. Which is ok, up to that point. Like all devices, that feature can go wrong. That should not be an issue – pilots are trained to recognise things going wrong and take action to correct them – perhaps by turning off the offending system. But Boeing did not provide adequate training/documentation to cover this rare event. Several pilots who had… Read more »

Rob Moss
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Rob Moss

It’s the software. It’s a race condition, pure and simple, and occasionally that race condition can cause an unrecoverable nosedive. Race conditions are notoriously hard to unearth until something goes wrong.

I’m both a software engineer and an Air Crash Investigation obsessive.

Many planes are aerodynamically unstable – the Eurofighter, for example, is deliberately so. They all have software to correct the aerodynamic instabilities, and that’s how we have planes that fly further, faster and cheaper. However, if you get that software wrong, it’s unsafe. Fix the software and you fix the problem.

Dodgy Geezer
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Dodgy Geezer

Since you have made a study of this, can you tell us whether it is the MCAS or AoA system software that is at fault?

thammond
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thammond

Not buying it. How do you move the undercarriage forward and “higher” (?) without redesigning most of the wing? And once it is retracted, how does it influence the aerodynamics that much? The tracks show everything was fine until the autopilot was switched on. So how can it be an aerodynamics problem?

Dodgy Geezer
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Dodgy Geezer

Without looking at the problem in detail, the wing is full of spaces where various items like fuel tanks and the undercart are placed. The OP says that the ENGINES were mounted forward and higher – NOT the undercart. All of this repositioning will change the CoG. maybe dynamically – if you have to shift a fuel tank off the centre line, the CoG will alter in flight. THAT is the aerodynamics problem. Once you have this problem, you have to correct it, and that is what the MCAS system does. But the MCAS has a problem if the AoA… Read more »

Matt
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Matt

You also move the centre of thrust.