Originally Posted by
layman
Not directly comparable, but the "impossible" inflight deployment of a thrust reverser on the Lauda Air 767 showed a couple of things:
1. the impossible does happen
2. a deliberate test of deployment of the thrust reverser at 10,000' was controllable while a deployment at the more realistic altitude of 30,000'+ was not
Will Boeing be conducting a certifiable test of one, then both wing tips, folding at operational altitudes and weights?
And, if you want to be really perverse, what if one or both became unlocked? Would the tip 'flap'? If so, what impact would / could that have on flight dynamics and structural integrity?
In-flight deployment wasn't certified to be 'impossible' prior to Lauda, because it was considered to be controllable. After Lauda, the T/R system was modified to make it 'impossible' since it was demonstrated to not be controllable.
BTW, what made Lauda uncontrollable was that it deployed at max climb power - the 10k flight test was with the engine already at idle. By design, the FADEC limits thrust to idle with the reverser in an uncommanded position, but aircraft control was lost and the aircraft started to break up before the engine reached idle. Oh, and it wasn't "30,000'+", it was 24k, Mach 0.78.
I don't know what the Boeing plan is for certifying the folding wingtips is - if they are going to certify 'impossible', or show it's controllable. But there are a number of systems on an aircraft that can cause a crash if they malfunction in the wrong way. All this focus on one system - which I seriously doubt has catastrophic failure modes - is a classic case of missing the forest for the trees. The very sort of thing that caused the FAA to miss the consequence of MCAS while going over other systems (that have never resulted in a catastrophic accident) with a fine tooth comb (and yes, I have first hand knowledge of that last part).