Originally Posted by
L39 Guy
FCeng84 earlier in this thread provided a really good explanation of what MCAS is all about; it's not there to provide a "feel" but rather to provide positive stability at high angles of attack (alphas). This is FAR's, EASA and every other certification agency requirement that the aircraft not be neutrally stable (nothing happens) or negatively stable (gets worse) near the stall but instead is positively stable (gets better but lowering the alpha). It only kicks in near the stall, assuming the sensors are working properly.
An MCAS failure, owing to the sensor failure (birdstrike or whatever other cause), causing the nose to pitch down in manual flight with the flaps up, presents identical characteristics to the pilot as a stab trim runaway (nose down) which has been taught on this aircraft forever. I can see why Boeing did not want to complicate things by creating a separate MCAS procedure as this would cause pilots to try to differentiate between a classic stab trim runaway and an MCAS failure while the aircraft is out-of-control. And since the emergency response is identical there is nothing to be gained either by trying to diagnose the problem in the air.
Although it might be politically more correct (optics) to insist on simulator training as the Transport Minister in Canada is doing, what is one going to practice? Airspeed Unreliable, which is part of the training and type certificate already? Stab trim runaway, which is part of the training and type certificate already too?
Except it’s not the same. MCAS does not present itself as a standard runaway trim. It only works with flaps up. It doesn’t trim non stop. And it trims with high speed where a normal trim trims with reduced speed.
It’s a different animal and doesn’t bite the same way.