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Comment by WalterBright | Hacker News Reader

There's nothing wrong with the concept of MCAS. Just it's implementation.

There's a lot wrong with the existence of the MCAS being a lie on top of a compromise made for other compromises. Being inessential if it was not born on the love of 'not doing it right because it is difficult'. Additionally it was f*d up in the process, yes.

There is a lot wrong with a plane intended to transport people that requires such a system in order to be safe to fly.

It requires the system to avoid training pilots.

And, yet, it does require proper training after all...

Only training to do what they are supposed to do anyway - use the cutoff switches when experiencing runaway trim.

I don't know, I feel like designing a system to prevent a pilot from lifting nose too high up seems to make more sense than a system that actively pushes the nose down after it being lifted. If nothing else, passengers would feel a bit of a discomfort of a sudden nose down movement. Not sure if I missed something in the current design.

> I feel like designing a system to prevent a pilot from lifting nose too high up seems to make more sense than a system that actively pushes the nose down after it being lifted

Lifting the nose too high can induce a stall, which is very dangerous at low altitude.

Yep. Also pitching the nose to far down to prevent a stall.

No it's not about comfort. MAX engine shroud is too far forward to the point it act as canards creating pitch up force at high AoA, in a self reinforcing manner into a belly up into irrecoverable stall. MCAS prevents this by quickly pushing nose down back into airstream.

I believe there were discussions earlier on that the FAA requires all civilian airliners to have positive static stability, aka CoL comfortably behind CG so air resistance straightens the attitude without inputs.

The opposite of positive static stability is Fly By Wire based 4th-gen onwards jet fighters like F-16, that has CoL only barely aft of CG, that replace aerodynamic stability with electronic PID controllers multiplexed with manual axis inputs for each axes. Those planes could go into a spin over some axis that make sense if at any moment FBW loses control.

The fact that MAX needed MCAS, an FBW-like system, to meet FAA standards is itself wrong, and implementation to make it a ghetto nonredundant trim system rather than full FBW is also wrong.

> into irrecoverable stall

My understanding is it wasn't enough to push it into a stall, the MCAS would just moderate the pitch up slightly so it behaved like the 737.

> to meet FAA standards is itself wrong

The FAA mandates that all jet airliners since the 707 have a yaw damper to correct for "dutch roll" instability. Augmented controls are normal on jets.

> The opposite of positive static stability is Fly By Wire based 4th-gen onwards jet fighters like F-16

The risks introduced by fighter jet lack of static stability are mitigated by the installation of ejection seats. That's a tough sell for passenger aircraft.

The 737 MAX is statically stable. There are quite a lot of uninformed comments floating around that compare the plane to fighter jets like the F-16, but these are pure nonsense. An F-16 would tear itself to pieces in seconds if the flight control software malfunctioned.

It seems more to be that people use the word "stable" while maybe another word should've been used. The main criticism during the "stable" criticisms is that something like MCAS was added. The design of the plane should've been in such a way that MCAS wouldn't be needed. So instead of adding MCAS, the problem leading to MCAS should've been solved with a (huge) redesign.

Note: Purely responding to the "stable" word. If people compare it to stuff like an F-16, then yeah.. they don't know / nonsense.

>MCAS, an FBW-like system

As WalterBright says, there is nothing 'FBW' about stability augmentation systems. In various forms these have been installed on all commercial jets for decades. 'Fly by Wire' simply means that there is no mechanical/hydraulic linkage between the stick and the control surfaces. The 737 MAX is not an FBW aircraft by any stretch of the imagination.

Its implementation and the corporate culture that pushed for that.

Just as there's nothing wrong with communism, just the Soviet Union's implementation.

> Just as there's nothing wrong with communism, just the Soviet Union's implementation.

There are many who would make exactly this argument, FWIW.

Do they all happen to work for Boeing?

Have you seen a good implementation yet?

In the US: https://en.wikipedia.org/wiki/Twin_Oaks_Community,_Virginia

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