Old 1st Jan 2019, 23:15
  #52 (permalink)  
wiedehopf
 
Join Date: Jul 2014
Location: Germany
Posts: 331
Originally Posted by Machinbird View Post
Finally, consider the intermittency of the problem. Different presentations (or lack of presentation in 1 case) of the problem over the course of 5 flights. During maintenance, the problem would often fail to present itself, and only leave its calling cards. This level of complexity shouts intermittent electrical problem, loud and clear.
While i agree that an intermittent electrical problem may well have been present, the coincidental 20 degree offset connected to the replacement of the sensor is quite stunning.
So the intermittent electrical fault might have nothing to do with the offset at all.
Also a constant exact offset of 20 degrees does not fit at all with an intermittent problem.

Your supposed electrical noise could be wind as well that is coming from one side while taxiing. Maybe it is gusty and therefore producing the "noise" you see.
The temporal resolution of the FDR readout is far too bad to conclude that that is electrical noise.

The imbalance in the sensor could be such that it is apparent when taxiing over rough taxiways creating the "noise" but is irrelevant as soon as the airspeed picks up on the takeoff roll. Aerodynamic forces far outweigh any inbalance at those speeds.
Such imbalance could be created by violently attaching the sensor. Or bending/breaking the vane.

And yes i find gross incompetence and negligence far more likely than an electrical error producing a 20 degree offset.
But i will entertain the idea gladly and ask you how an electrical problem could introduce such a fault?

The SMYD has two inputs for the AoA sensor, labeled sinus and cosinus.

This for me points to a resolver.
https://en.wikipedia.org/wiki/Resolver_(electrical)

Now i really have no idea how an intermittent or basically any electrical problem would introduce the 20 degree offset.
Do you have an idea?
(I'm happy to be corrected on the points made, it's about the puzzle less about being right in my opinion)
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