Originally posted by AlphaZuluRomeo ...
The ABNORMAL ATTITUDE LAW is triggered if (non exclusive list):
- the [measured I presume] speed is below 60kt
- the AoA is above 30°
Per the BEA note, at each time after the beginning of the final descent, one of these two conditions was met.
So the ABNORMAL ATTITUDE LAW should have triggered, meaning the auto-trim was lost, hence the THS stayed "stuck" at 13° value.
My question for those in the know : Does the ABNORMAL ATTITUDE LAW activation also trigger a message indicating to the crew that the auto-trim is unavailable ?
In the first instance, you should be made aware of a
Flight Global report attributed to the BEA.
Secondly, the FCOM provides the following statement on ABNORMAL ATTITUDE LAW -
An abnormal attitude law in pitch and roll is provided, if the aircraft is in flight and in any of these conditions:
- Pitch attitude > 50° node up or 30° nose down
- Bank angle > 125°
- Angle of attack > 30° or < - 10°
- Speed > 440 knots or < 60 knots
- Mach > 0.96 or < 0.1
The law in pitch is the alternate law without protection (except load factor protection) and without auto trim. In roll, it is a full authority direct law with yaw alternate.
After recovery, the flight laws are:
In pitch : Alternate law.
In roll : Direct law with yaw alternate.
First reading of the above leads one to believe that each of the conditions is mutually exclusive, but if the Flight Global report is to be believed, that is not the case. The new interpretation is that the conditions are mutually exclusive PROVIDED all the ADRs haven't been rejected, but should all the ADRs be rejected, then an inertial upset involving either of the first two items will revert the aircraft to ABNORMAL ATTITUDE LAW.
If this was the case, the MANUAL PITCH TRIM ONLY was not displayed, as auto trim was still available.
Don't take it all as "gospel", as that is not what the FCOM currently says.
EDIT :: See
post #1571 by
A33Zab for details.