Originally Posted by
VicMel
I agree that loss of a vane is questionable for 2 reasons:-
1) The idea that there are 2 (or 3) different AoA sensor faults were experienced on the 2 Lion Air flights and ET302 flight seems to me to be very unlikely from a probabilistic point of view, especially so as the AoA sensor is apparently generally very reliable.
I think the “lost vane” idea came from an observation on ET 302’s FDR Data chart that Vertical Acceleration lines up with a jump in AoA. It is possible that “cause and effect” may have been misinterpreted here because Vertical Acceleration is a consequence of, and directly related to Pitch Rate. This would fit in with the fact that AoA L was disrupted on the 2 Lion Air flights (as well as on ET 302) just around take off when there would have been a large value for pitch rate.
Well, how does that align with ALL the information?
At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording.
At 05:38:43 and about 50 ft radio altitude, the flight director roll mode changed to LNAV.
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.
There is very little in terms of cause and effect that would satisfy the heater parameter change other than losing the vane itself. (Unless you want to believe this is entirely spurious).
- GY