Originally Posted by
meleagertoo
This sort of thing could be significant. If the Alpha vane had been knocked off in a birdstrike I wonder how long it takes to trigger an overheat if there is no vane left to dissipate it? You can bet someone has found out, and if that figure is close to 4min 12 sec it's an indication that might point to the alpha vane physical loss theorey.
This was discussed at length somewhere around post 4000 (3000?), a lot of details can be lost in a massive thread, a brief recollection:
The DFR shows initial AoA fault occurs at 5:38:45 followed shortly after by "Primary AOA Heat L" going to off.
Quotes are from the prelim report:
At 05:38:46 and about 200 ft radio altitude, the Master Caution parameter changed state. The First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded Left AOA Heat parameter changed state.
The heater is in the vane so when the vane departs the circuit would open, this would cause the above.
At 05:42:51, the First-Officer mentioned Master Caution Anti-Ice. The Master Caution is recorded on DFDR.
At 05:42:54, both pilots called out “left alpha vane”.
I don't know the system but assume there was a display of Anti ice caution cause.
This was the second master caution, I will leave it to those with more knowledge whether this was a simple repeat of the first (unacknowledged?) or was re-triggered by other events. Totally reasonable for the crew to not prioritize an anti ice caution at takeoff given the conditions, this would only matter at high altitudes.
The other evidence that strongly supports vane departure theory is the last part of the DFR plot where the left AoA sensor can be seen closely following G forces, caused by the internal (vane) counterweight acting as a pendulum.