November 29, 2019, ©. Leeham News: We continue the series about the Lion Air JT610 crash by now analyzing the final part of the flight.
We try to understand what changed when the First Officer took over the flying from the Captain and why the aircraft subsequently crashed.
We analyzed the initial part of Flight JT610 over the last weeks, based on the extensive data and information available in the final crash report issued by the Indonesian National Transport Safety Committee.
Now we look at what happened when the Captain asked the First Officer (FO) to take over the flying.
First, why did the Captain hand a difficult to fly aircraft to the FO?
The report describes the events and communication in the cockpit during the crisis. At all times up to handing over to the FO, the Captain was confronted with new weird alarms, indications, and behaviors in the cockpit. For example; at a PFD speed of 306kts the audio warning “ AIR SPEED LOW-AIR SPEED LOW” went off. This is the warning you get before you get stall warning, next thing is stall warning and stall. Stall warning was on but no stall indications like shaking aircraft came.
When he got this warning his own stall speed tape on the PFD (the so-called “totem pole”) met the high-speed warning tape, something you see only at very high altitude (they were at 5,000ft). Overall, it was a constant blaring of warnings and strange indications. The only warning which might have explained the mess had gone missing for Boeing in the migration from NG to MAX, AOA DISAGREE.
Then as the flaps were retracted at 5,000ft it got even worse. On top of all the warnings, disagreements and wild speed tapes, the flight controls went weird. MCAS started its nosing down and the crew had no information whatsoever something had changed for the MAX. It was the same old 737 and both had more than 5,000 hours on it. They could rightfully think they should know all about it.
From the conversation from the Captain (who was the Pilot Flying (PF)) to the FO (who was the Pilot Monitoring, PM) it was clear he was totally busy countering the attacks of MCAS amid trying to understand what was happening. The aircraft got weirder and weirder.
The First Officer, who was the Pilot Monitoring and by it the one who should work on the fault-finding with the help of the Emergency checklists, made little progress in completing the checklists for the warnings and fault indications the crew had.
Apparently, to shift tasks the Captain asked the FO to take the controls. He didn’t give instructions on how to handle the repeated nose downs from the aircraft, however. This seems strange. There are several possibilities why this didn’t take place (the previous flight Captain didn’t either, see below).
It’s possible the Captain countered MCAS rather instinctively. It’s an automatic reaction for a pilot to neutralize an aircraft nose down with an opposing stick force followed by an instinctive manual trim. This is also what Boeing’s safety analysis concluded. Trim cutout was available in addition but was not a factor in the analysis.
The nose-down was only one weird action of the aircraft among many. We know today it was the key one for aircraft safety. But we have got a full explanation of MCAS and how it works. How should they know? The multitude of faults didn’t make sense as there was no AoA warning. The Captain certainly didn’t understand what was wrong with the aircraft at this point.
When one goes through all that happened before he handed over to the FO it’s easy to see why he could not single out erroneous trimming as the key problem. What happened was not a trim runaway situation. The trim worked fine.
Trim Runaway is trained in almost every simulator session for 737 pilots and it means the trim runs uninterrupted in one direction and can’t be stopped with manual trimming. MCAS did not run uninterrupted, the Captain could trim against, then everything was normal. Then the nose got heavy again and it was time to hold against and to counter with trim. Then everything was normal again, …..
To assume pilots would identify this as trim runaway was a clear fault by Boeing and FAA. The Captain who lived to say what he thought it was, said it was “Speed Trim confused by the faults in airspeed information”. This is the logical conclusion when one has no knowledge of MCAS existence.
Re. the Captain’s handover to the FO. The previous flight Captain asked the FO to take over so he could analyze what was wrong. He gave no special instructions for this handover. The FO ran into the same problem as the FO of JT610, he trimmed too short against and got a stick “he could almost not hold”. The Captain then experimented with the trim cutout switches. It stopped the nose down movements.
The Captain of the accident flight never got this far. The FO trimmed against too short a time and the horizontal stabilator gradually outcompeted the elevator. For the pilots, it felt like the flight control system was now forcing the aircraft to dive. Both pulled on the yokes at full might during the final seconds as the aircraft headed down. Why didn’t they trim? It was a matter of seconds and then you just pull. Trimming comes after pulling.
One can conclude a few things from the above:
For after the fact pilots to come and say it was obvious what was to do is only showing they haven’t immersed themselves in the no show of the only sensible warning available and the total cascade of non-sensible warnings. In addition, they have a problem imagining how to understand something which they don’t have any information about and the efficient masking of this unknown by its donor process, Speed Trim.
It was far from clear what to do and many flight crews would have ended up where JT610 did in my opinion. In the next Corner, we shall discuss why the fixed 737 MAX is a very different story from the above.