Originally Posted by
Tomaski
Re MCAS overriding the crew - it was, in fact, the opposite. The Main Electric Trim (MET) overrode MCAS ever time it was used. As we saw when the Captain was the PF, aggressive MET inputs could counter MCAS inputs. That said, it is apparent from the report that while the Captain was actually making these inputs, he was not articulating what was happening with the trim, likely because of cognitive overload. When he transferred control to the FO, it was without any warning that the stab trim was acting in a peculiar manner. The FO was not nearly as aggressive in making MET inputs. This is not surprising since those types of inputs were outside his normal experience. The FO got increasingly behind the MCAS inputs and ultimately lost control.
Re the AOA DISAGREE annunciator. The AOA DISAGREE function was not operational on the accident aircraft, but its presence would likely have made no difference except for adding yet another warning light to the mix. By design, this annunciation, if working, would not have come on until 400' AFE. During the accident flight, the FO announced the IAS DISAGREE warning within one second of liftoff and the ALT DISAGREE warning within 30 seconds. At the time the ALT DISAGREE annunciation appeared, the Captain's altimeter read 340 feet and the FO's altimeter read 560 feet (Jakarta is very near sea level). Thus an AOA DISAGREE message would have been approximately concurrent with the ALT DISAGREE annunciation.
There is an AOA DISAGREE non-normal procedure, but it is not a memory item. That non-normal checklist, if consulted, would simply directs the crew to the IAS DISAGREE and ALT DISAGREE non-normals. The IAS DISAGREE non-normal directs the crew to the Airspeed Unreliable non-normal. Thus, if the AOA DISAGREE warning was operative, it would not have added any useful information from a procedural standpoint as ultimately the checklists direct the crew to the Airspeed Unreliable procedure. The Captain called for this procedure less than one minute after the IAS DISAGREE call by the FO. If the AOA DISAGREE had illuminated, and the crew had consulted the associated non-normal before doing anything else, it would have potentially delayed their response to the Airspeed Unreliable event.
Many thanks for taking the time to explain , Best R