JRBarrett
The analysis by “Satcom Guru” is intriguing. He has found that the digital representation of AOA in the 737 is expressed as a 26 bit binary word, and if the 26th bit becomes incorrectly set (goes from binary zero to binary 1), it will correspond to an AOA of exactly 22 degrees, which is what the FDR on the Lion Air flight recorded for the left AOA sensor.
I strongly suspect that there was nothing wrong with the AOA sensor on LionAir - but rather some kind of intermittent hardware or software fault in the downstream conversion of the position data from analog to digital. If this also happened on Ethiopian, then the cause of this possible data corruption is going to have to be found and corrected on the Max in addition to any changes made to the MCAS system.
VicMel
Hence my concern:- Because MCAS software was not produced to Level A, it is not assured to be at a high enough standard to allow it to directly control the stabilizer. The risk is that there could be a fault in the software that could cause an erroneous trim condition. The proposed patch may not have any effect on such a software fault.
Alchad
If I were a betting man, I would put a few pounds on this suggestion. Failure of the AoA sensor seems to being clutched at like the proverbial man and a straw, but I've yet to see anything which confirms this. Let's hope Boeing are also pouring over the code with a very fine toothcomb.
Peter Lemme (Satcom Guru) has also commented on the AoA versus software issue.
The replacement of the identified "faulty AOA" sensor with another AOA sensor immediately before the Lion Air crash did not prevent the same "faulty AOA" sensor signal from reoccurring.
And why was the AOA faulty signal accompanied by similtaneous altitude, airspeed disagree indications along with PCU fault?
I agree that this all seems to be pointing at faulty sensor signal conditioning or processing in the air data computer software.