Originally Posted by
silverstrata
A high speed stall is not the same, as the elevator will still have a lot of authority at those higher speeds. MCAS was designed for a slow speed stall, when engine thrust combined with engine aerodynamic pitch-component, could and would exceed elevator authority and send the nose skywards. The MCAS is an anti home-sick-angel device.
The trouble is, as soon as it lowers the nose and gains speed, MCAS turns into a super gravitational attractant. Unless you can take all that forward trim off in a few seconds, your shiny 737 becomes a Stuka in terminaI dive mode. I still have no idea how anyone certified a device that would give a slippery passenger jet, full forward trim. And give that trim, when the aircraft is likely to end up 20 degree pitch down, and gaining speed rapidly.
Especially when the QRH (and I presume the Max QRH) says do not use too much trim in an incipient stall, as the aircraft may become uncontrollable. Actual wording for the approach to stall is:
And yet that is exactly what MCAS is giving you. I fail to see how Boeing can dodge this important issue, and not be forced to make major amendments to the MCAS system. At the very least MCAS should stop trimming at a safe point where a recovery from a dive is still possible - say 3-units on the trim indicator....!!
Silver
Edit: As to Zzuf’s question about why not fit a stick-pusher instead, I suspect this was a certification issue. If Boeing had admitted a stick-push was required, then a lot more certification would also have been required. But if you slip in a trim-pusher by the back door, then perhaps nobody will notice....
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It seems as though it was designed for steep turns also. I'm guessing that the test pilots rolled and pulled and then they didn't have to pull so hard or had to neutralize as the engines aero effect added pitch input. "
The MCAS function commands nose down stabilizer to enhance pitch characteristics during steep turns with elevated load factors"