Originally Posted by
AGBagb
From the Synopsis (quoted above) of today's Interim Report, about the previous flight:
The PIC noticed the aircraft was automatically trimming AND. The PIC moved the STAB TRIM switches to CUT OUT and the SIC continued the flight with manual trim without auto-pilot until the end of the flight.
And here's a good example of the problem with relying on synopses, executive, summaries and the like; sometimes they leave really important stuff out.
In the body of the report between '
The PIC noticed that as soon the SIC stopped trim input, the aircraft was automatically trimming aircraft nose down (AND).' and '...
the PIC moved the STAB TRIM switches to CUT OUT.' there is,
inter alia, this line;
After three automatic AND trim occurrences, the SIC commented that the control column was too heavy to hold back.
(My bolding)
If you look at the version of FDR data presented to the Indonesian parliament (but curiously not in the preliminary report) it details control column force measurements. At the onset of JT43's MCAS event the control column forces rise rapidly to around 85 (out of 100) of whatever the units of measure are (can someone comment on that parameter and the units of measure?). In normal flight the forces bounce around in the 5 - 15 range so I'm assuming that 85 is, well, attention grabbing. For JT610, until the terminal 90 seconds or so, the forces never get above 50 units and tend to bounce around the 25 mark. I suspect that it was the control column forces that prompted the STAB TRIM switches being moved to CUT OUT on JT43, something that probably didn't occur on JT610 until the terminal (too late) phase.
It is one of a couple of differentiating factors that you can put down to JT43's decision to maintain their climb while dealing with their problem and JT610's decision to level off at 5,000 feet to deal with theirs. I strongly suspect that the latter was part of a briefed plan to deal with a possible UAS on take-off. I don't think that it is happenstance that JT610 '...
requested approval to the TE controller “to some holding point”' as well as advising '...
the TE controller that the intended altitude was 5,000 feet.' and that they re-retracted flap at 5,000 feet. There is level flight pitch and power data for holding, flaps up at 5,000 feet in the Flight With Unreliable Airspeed tables. In fact, 5,000 feet is the lowest altitude for which there is data for level flight.