PPRuNe Forums - View Single Post - Ethiopian airliner down in Africa
View Single Post
Old 8th Apr 2019, 02:50
  #3566 (permalink)  
Derfred
 
Join Date: Jun 2006
Location: Brisbane
Posts: 265
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by deltafox44
i would speculate that it will activate upon resetting the stab supply switches
...
The FDR plots indicate that it didn’t. There was no further activation of MCAS until 5 seconds after the final two yoke switch inputs.

Furthermore, it is apparent that MCAS is unaware of the position of the stab cutout switches, because it still tried to trim while the switches were in cutout.

So I would speculate that MCAS wouldn’t have a clue that the cutout switches had just been reactivated, and would only attempt to trim again when the already published criteria are met:

1. AOA still exceeding threshold, and
2. Reset by subsequent pilot activation of yoke trim switch.

So, in theory, a pilot with superior understanding of MCAS could:

1. Hit the cutout switches in response to undesirable MCAS input,
2. Hold back pressure to keep the aircraft safe while collecting thoughts,
3. Reactivate cutout switches,
4. In his own good time, then electrically trim ANU either continuously or in “blips” spaces less than 5 seconds apart,
5. Hit the cutout switches again less than 5 seconds after the last “blip”.

Now, with an aircraft “in trim”, continue with manual trim.

Speaking purely academically of course.


Last edited by Derfred; 8th Apr 2019 at 03:02.
Derfred is offline