Can somebody with a deeper knowledge of the 777 design explain, how the flaperons are prevented from flutter? It looks like they are not mass-balanced, so obviously they use the actuators for damping. Are there "loss of hydraulics" screarios, which could lead (during a longer descend from cruising altitude) to loss of damping? Is it enough to have hydraulic fluid in the actuators, or do you need hydralic power? Or at least a certain amount of remaining hydralic pressure in the lines? Then the flaperon may have been lost during the late high speed gliding phase due to flutter, which may explain why it is the only larger piece of debris not totally torn to pieces during impact with the ocean.
How much vibration is created by the wake of a stopped engine, is that enough to destroy the flaperon fittings in a low cycle fatigue scenario if gliding at high speed for a longer period?