On 1/20/22 20:45, Keenan Tims wrote:
The AOA DISAGREE alert was never intended as an optional feature. However either due to a software bug or miscommunication between Boeing and their contractor for the avionics package (Collins?), it got tied to the optional AoA (value) indicator. This was caught *by Boeing* and reported to the contractor, but Boeing instructed them not to fix the problem and defer it to a later software update 3 years later, and never bothered to notify operators or the FAA about the problem.
In my mind, that is still rather negligent and irresponsible, especially because in the -MAX, this was more critical considering the level of input from the computer to activate MCAS outside of the pilot's control, or even knowledge. Unlikely to be such a big deal in earlier B737 models, where MCAS is not used.
Somehow it's even worse this way. I don't think a working DISAGREE alarm would have saved the flights, though.
There has been AoA sensor failure in non-MAX B737 aircraft. The difference is you don't have MCAS there trying to do its own things. Of course, had an AoA sensor failure and/or "AoA Disagree" scenario been tested and trained for, particularly on the -MAX, it would have been fairly obvious to both the Lion Air and Ethiopia crew that troubleshooting for a "Runaway Stabilizer Trim" would likely have saved their lives. Of course, troubleshooting for a runaway stabilizer with MCAS involved also has its nuances, depending on air speed, aircraft configuration, e.t.c. Mark.