Originally Posted by
Flapsupbedsdown
Question: if you are faced with an IAS disagree at "say 200 ft agl" ( there is a memory item for this) why would you retract flaps and accelerate? MCAS wouldn't even come into play. Not defending manufacturer or controlling agency. In my very humble opinion even Sully's most appreciated comments are not appropriate.
How a flight crew would respond in the situation will be a function of what they know about the underlying system and how they have been trained to execute this procedure. There are major deficiencies in both areas.
Prior to Lion Air, information on MCAS was not available to flight crews, so they could not base any decision on what to do with the flaps on information they did not have. In the case of Ethiopian 302, the information regarding flap extension inhibiting MCAS was available, but there are serious questions as to whether this was adequately communicated to the Ethiopian pilots.
The Airspeed Unreliable procedure is very generic, and it does not provide much in the way of takeoff-specific guidance. In particular, there is no firm guidance on whether to leave the flaps extended while the checklist is being run or whether to retract the flaps at the normal point (while setting appropriate pitch and power settings from the tables). Given the available information, reasoned arguments can be made for either choice regarding the flaps.
More to the point, I strongly suspect that neither of the accident crews had ever been exposed to an Airspeed Unreliable event in training, and therefore were not aware of all the various warnings and indications, nor were they provided with specific guidance on how to execute this procedure. I will speculate that they all ultimately chose to retract the flaps because 1) they had accelerated past the flap placard speed (generating an overspeed clacker), and 2) they were used to raising the flaps in absence of any guidance to do otherwise.