Originally Posted by
alf5071h
‘To use an analogy, there was a time when the hazards of low-level windshear and microburst phenomenon were not well-appreciated. Now we practice windshear recoveries all the time because prompt recognition and response can be critical to a successful outcome. Why do we not do the same with Runaway Stab Trim? It is a "memory item" after all.’
We might not be able to avoid wind shear / microburst, although we should make every effort to do so (wind shear avoidance training?).
Runaway trim in the 737 Max is currently not avoidable, and in some circumstances unrecoverable, but could be with a modified trim system.
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Pilot training requirements are not meant to compensate for non-acceptable design on the compliance and safety standpoint.”
https://www.easa.europa.eu/newsroom-...-clarification
Alf
i don’t think runaway stab is avoidable on any type? Certainly not on any 737 or even 707 for that matter.
Any electrical input can trigger the motor and if that input, false or otherwise , doesn’t stop, the stab keeps running.Manual elec. trim, autopilot trim, Mach trim, STS trim or MCAS trim all have the potential to initiate a runaway. It’s not just a Max issue although MCAS is on max only.
Unrecoverable? Don’t think so. Even on the Lionair the previous day it was indeed recovered using the correct procedure,
albeit with the aid of a third party jump seat pilot who clearly DID know what to do. I hope he has illuminated the investigation with his private knowledge.
Is that a fair comment? If not I’m genuinely keen to know why? We seem to have forgotten the one that got away.
And a modified MCAS will reduce any chance of that alpha vane induced failure mode occurring again, but will not remove any other cause.
So I would rather fly with a crew that can handle a runaway stab whether continuous, intermittent but repetitive, any undesired and uncommanded movement of the stab that is not normal and which is starting to upset the aircraft basic trim state. It’s the trim moving in such a way as to cause the plane to deviate from its desired path -uncommanded -which tells you it’s misbehaving. At least it was when Pontius was a pilot. And nothing has changed aerodynamics since then.
Cheers
y