Originally Posted by
MurphyWasRight
Working from memory, since I don't have time to track original posts at the moment, I believe this was reported by Southwest and possibly others.
I don't think we know if this was discovered by Boeing testing before it was reported, possible it was missed since it does work if the optional AoA display is pressent.
It was deemed non critical and was scheduled to be fixed in a standard SW upgrade cycle.
It would actually be a bit unusual to notice that a disagree warning was not working unless there was a case where an AoA failure happened (bird strike/whatever) and someone noticed the lack of warning. A human factors factor is that it is usually harder to notice something missing than an an unexpected occurrence.
Since it is implemented in software I doubt it would be a line item in a maintenance check unlike the old days when a similar alarm might have relays and light bulbs in the mix there would be nothing specific to the AoA disagree alarm that could fail. With a big 'assuming' it worked at all of course.
My understanding is that testing a single AOA sensor on the ground is rather difficult, and requires specialised calibration equipment.
Testing an AOA disagree circuit requires two simultaneous readings, and doing so seems far beyond the scope of any normal airline maintenance requirements.
It is very hard to prove a 'negative' result by testing, and IMO it is not at all surprising that the missing AOA disagree function wasn't picked up earlier.