Wonkazoo posts:
At the moment that the PF handed off control of LT610, MCAS was in the MIDDLE of an 11-second run....
First of all, MCAS doesn’t run for 11 seconds - ever.
Next, you have misidentified where the change in control took place. As I understand it, you’ve never been part of a two-person airline crew, so I can understand if you are not familiar with the protocol. I suspect that you are instead focusing on that blue vertical line that was added by the author of the Leeham article you have cited, but the author was actually marking another event.
Whenever aircraft control is transferred in a multi-crew aircraft when the autopilot is not engaged, the proper technique is to first place the aircraft in a neutral trim state (i.e. no control pressures, represented by the spot of relative calm on the CCCForce FDR trace before the blue line)
and then make the hand-off (procedurally accompanied by some verbalization such as “You have the aircraft” “I have the aircraft” though this part is sometimes omitted). Ideally the pilot on the receiving end would not have to make any immediate control input. A pilot does not, I repeat does not, transfer control when there is an ongoing control input or out of trim state. That would be a significant error.
We know that MCAS will pause for 5 seconds after a Main Electric Trim input. We can see by the FDR traces that the Captain was making aggressive Main Electric Trim inputs to keep the the stab in a properly trimmed position. Thus the proper sequence of events would be that the Captain trimmed up the aircraft, and during the subsequent pause he would have transferred control to the First Officer. The FDR does not break out the separate Capt and FO trim inputs, but as the Leeham author points out, the “CCCForce” red and green lines give a good indication where the primary control forces were originating. The vertical blue line indicates the first significant control input the FO made in response to MCAS
after the change of control. It was
not the moment of the change in control.
When MCAS activated there was a slight delay in the FO’s response, as one might expect. After this point he responded with aggressive elevator inputs (height of the green CCCForce line) and only minimal stab trim input. This was the opposite of the Captain who used much less aggressive elevator inputs (height of the red CCCForce line), and much more aggressive trim inputs.
From that point on, the FDR traces tell the rest of the story. The First Officer fought MCAS primarily with elevator inputs and only ineffectually with Main Electric Trim inputs. As a result, the stabilizer worked its way to an untenable position resulting in loss of control. Why the Captain did not pick up on this struggle is a bit of a mystery. It is possible he went immediately went “heads down” into the QRH (Quick Reference Handbook) and didn’t realize the FO was losing control until it was too late.
An alternative explanation that might also explain the divergence in the two CCCForce lines (the so-called “malfunction”) is that the Captain may have been bending over to pick up something off the floor (like his QRH manual) or was contorting his body around to get this manual out of his kit bag (stored behind and to the left) or perhaps reaching for the stick shaker circuit breaker behind him and, as a result, part of the Captain’s body was in between the control column and the seat. If the FO yanked back on the control column with great force at this moment, he could have pinned the Captain in place, possibly causing injury. This effective push/pull on the control columns would have registered as a force divergence. It would have happened quickly and may have added an additional distraction with a possibly injured Captain and an FO mishandling the aircraft. Of course, this is all speculation at this point, but hopefully the CVR would add some clarity.
The inflection point in the aircraft state that occurred at the point of aircraft control provides a critical lesson about why the first three pilots succeeded, and the next two pilots failed, to manage the erroneous MCAS inputs. The Captain clearly demonstrated that aggressive use of the Main Electric Trim could effective counter MCAS. The First Officer, on the other hand, demonstrated what happens when the pilot opts to use primarily elevator, and only limited trim inputs - MCAS will overcome the elevator if the stab is not kept in trim. We will see this behavior repeated by the Captain of Ethiopian302.
Since trimming the elevator and/or stab is such a basic and fundamental skill that any pilot - much more so one with a commercial certificate - should have wired deep into muscle memory, then it is very germane to ask what was different about the training, experience, and/or environment of the JT610 First Officer and the ET302 Captain that resulted in them not trimming when it should have been the most natural response to the control forces that MCAS generated.