Originally Posted by
EDLB
I take bets that it has something to do with the signal wiring form the AoA vane to the flight computer (ADIRU) like shorting out one half of the SIN or COS symmetric signal and creating with that something around a 45 degree/2 offset. If the Ethopian airline FDR does show a similar problem, then there is some latent harness, connector or ADIRU problem which will show up in the other 737 MAX made in a similar timeframe. So if that establishes, the investigation might look into some of the grounded planes build in similar timeframe.
In theory, (older 737s) each computer takes the three wires (the two analog signals) and amplify them, then demodulates them (turns them into DC) using the reference AC current that powers the vane, then filters them and finally go to an A/D converter. The values are stored at a memory block, and then a software block reads them, and translate them into a AOA (degrees (atan(sin/cos)), which is once more filtered (so two AOA are available, raw and filtered).
I would be really surprised if the software block did not, at that point, perform the plausibility check (sin^2+cos^2=vmax). (for instance, it shows a warning if the vane didn't move more than 3 degrees for a period of time).
But even if it didn't, shorting one of the signals to vref would produce 9 degrees offset at the vane. Does that translate to 22 degrees airplane AOA?