On the Ethiopian Crash Report

Robert Chapin
2019-04-05T21:34:08+00:00

The crash of Ethiopian Airlines flight 302 is certainly the most important event being discussed in the aviation industry today.

Having read the just-released investigation report, I now see several pieces of new information that will profoundly change the direction of this discussion.  For my part, I am making an armchair analysis of a preliminary, though official, report.  My expertise in some areas of aviation should not be taken as authoritative nor anything more than added speculation toward a very large media frenzy.

Critique of the Report Summary

While the latest Executive Summary seemed careful to avoid drawing conclusions, I was dismayed about the focus on details such as the Angle of Attack values and the crew’s request to return for landing.

Here was an opportunity to accurately summarize the content of the report while still remaining impartial.  For example, the summary simply stated, “The crew lost control of the aircraft,” but this is hardly an accurate summary of the reported data.  In fact, it appears the crew was struggling but did have control of the aircraft during the first four minutes of the emergency.

Similarly, the summary mentions stick shaker activation and, vaguely, “flight control problems”, when the only glaring control problem in the flight data recording was a series of Automatic Trim Down Commands that created a heavy control bias for the pilots to fight against.

The Elephant in the Room – Missed Opportunities

In retrospect, the Boeing Max fleet should not have been in operation after the previous Lion Air crash.  I can’t say this is easy for the aviation industry to accept, even now.  Before the second crash, there was simply not enough attention on the design flaws in these aircraft, and those in the industry who should have been made aware of the underlying risk were not made aware.  Possibly worse, the traveling public had no idea the severity of the problem.  I am not immune from this lack of oversight, as I found myself on the flight deck of one of these aircraft hitching a ride to work a few months ago.  Knowing what I know now, I would not have taken that flight.

Could the pilots of the Ethiopian flight change the outcome of their emergency?  I believe the answer is yes.  And this is certainly not meant as blame or evaluation of skill or training or their personal history in any way.  This is purely hypothetical.  One of the new documents available to the public through the preliminary investigation report is a copy of the Boeing Flight Crew Operations Manual procedure for Runaway Stabilizer.  In that procedure, very importantly:

Stabilizer trim wheel . . . . . . . . . . Grasp and hold

I don’t think I can emphasize this enough.  After recognizing the runaway trim condition, the pilots were supposed to intervene by physically stopping the motion of the mechanical trim wheel.  In the excerpt of the cockpit voice recorder information, and from what we now know of the flight data, this never happened.

So we have some critical new questions to investigate:

Why did the first officer state that the manual trim wheel was not working?

Was it possible for one or both pilots to grasp and hold the trim wheel while also fighting the elevator control column?

If so, is it possible that the outcome of this flight rested on the timing and clarity of the captain’s commands in response to the emergency situation?

Or, was this tragedy nearly unavoidable due to multiple safety system failures and missed opportunities to ground the Boeing Max fleet before this flight ever took off?

A Better Executive Summary

Immediately after liftoff, Fight 302 experienced malfunctioning Angle of Attack, airspeed, altitude, and flight director pitch indications of the left-side flight instruments.  This triggered an immediate activation of the Master Caution and the left-side stick shaker.  The captain, on the left side of the flight deck, was the pilot flying.  His initial response to the abnormal situation was to command the first officer, on the right side of the flight deck, to activate the autopilot system.  The captain made this command more than once, and the autopilot was working for a period of less than one minute during the climb after takeoff.  Two distinct and prolonged Automatic Trim Down Commands began immediately after the wing flaps were fully retracted to the zero position.  From that point, approximately four minutes elapsed where moderate nose-up inputs were applied continuously by the pilots to the control column.  After those four minutes, the electric trim system reactivated, as evidenced by two nose up trim commands by the pilots, followed by one more prolonged Automatic Nose Down Command.  The aircraft crashed approximately 20 seconds after this final trim command.

Further Reading

For a remarkable description of design flaws in the manual trim wheel system, see Vestigial Design Issue Clouds 737 Max Crash Investigations.

4 Apr 2019

Category:
Accident Reports

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