Originally Posted by
Tomaski
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.
The point that that KNKT were making regarding the absence of the AOA DISAGREE warning was not so much aimed at the accident flight, rather it was aimed at the penultimate flight, LNI043, in particular the likely post-flight maintenance actions.
It's addressed in Findings
63. The inhibited AOA DISAGREE message contributed to the inability of the engineer to rectify the problems that occurred on the LNI043 flight which were caused by AOA sensor bias.
and Contributing Factors
5. The AOA DISAGREE alert was not correctly enabled during Boeing 737-8 (MAX) development. As a result, it did not appear during flight with the mis-calibrated AOA sensor, could not be documented by the flight crew and was therefore not available to help maintenance identify the mis-calibrated AOA sensor.