View Single Post
Old 10th April 2019, 02:30 PM
David Knudsen David Knudsen is offline
Join Date: Mar 2008
Location: Brisbane
Posts: 712

Happy to stand corrected, but the way I understand it was that they were unable to exert enough force on the manual trim wheel (due to the airspeed) and reactivated the trim cutout switches.

At 05:40:35, the First-Officer called out "stab trim cut-out" two times. Captain agreed and First-Officer confirmed stab trim cut-out.

At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance of AND automatic trim command occurred without any corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches were in the "cutout" position
So that indicates with the switches in the cutout position, MCAS continues to operate but cannot move the stabiliser as the cutout switches de-energise the motor?

At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.
I assume the FO is confirming the manual electric trim is not functioning, consistent with the switches being in cutout, so tries the manual trim wheel without success (Due to aerodynamic forces of the aircraft being above VMO??)

At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,400 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units.

At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording.
So at some point between 05:41:54 and 05:43:11 the trim cutout switches must have been reactivated for the manual electric trim inputs to move the stab in the ANU direction - which explains why MCAS suddenly had the ability to command AND movements again?
Reply With Quote