Ethiopian Airlines Crew Followed Procedures Before Boeing Max Crash, Early Report Says (latimes.com)

The pilots of a doomed Ethiopian Airlines jet followed all of Boeing's recommended procedures when the plane started to nose dive but still couldn't save it, according to findings from a preliminary report released Thursday by the Ethiopian government. From a report: The plane crashed just six minutes after taking off from Addis Ababa, killing all 157 people on board. The report, based on flight data and cockpit voice recorders on the Boeing 737 Max 8, was not released in full. Boeing declined to comment pending its review of the report on the March 10 crash. The Max 8 has been under scrutiny since a Lion Air flight crashed off the coast of Indonesia under similar circumstances in October. Thursday's revelations raise questions about repeated assertions by Boeing and U.S. regulators that pilots could regain control in some emergencies by following steps that include turning off an anti-stall system designed specifically for the Max, known by its acronym, MCAS. Investigators are looking into the role of MCAS, whose functions include automatically lowering the plane's nose to prevent an aerodynamic stall. The Max has been grounded worldwide pending a software fix that Boeing is rolling out, which still needs to be approved by the Federal Aviation Administration and other regulators. Further reading: Flawed Analysis, Failed Oversight: How Boeing, FAA Certified the Suspect 737 MAX Flight Control System.

Comments

Next up:

[Narcocide]

They find out that some completely different bug causes the MCAS override to stay on even if you shut it off.

Either that or that it is susceptible to external control.

Boeing Deserves to Pay for This

[EndlessNameless]

So, to summarize:

1. Boeing self-certified that pilots certified in type did not require additional training. (Prior to the recent deregulation, they weren't allowed to self-certify.)

2. Pilots had to break out the manual during an emergency to properly control a system they were not trained to use.

3. The system either did not disengage properly, or else it reengaged automatically, contrary to well-established norms for this aircraft type.

Boeing screwed up, but it also happened because of relaxed oversight. The previous level of oversight seems more appropriate.

Perhaps the FAA Administrator who made these changes should be forced to resign. This administration has had enough turnover that the President should be capable of appointing new leadership quickly.

Re:Boeing Deserves to Pay for This

[Anonymous Coward]

There seems to be a lot of confusion around how the MCAS system is "disabled" in the case of problems. The MCAS system itself can't be disabled. The procedure for dealing with runaway trim adjustment, a larger umbrella under which problems with MCAS fall, is to turn off power to the electric motors that turn the trim adjustment wheels. These are physical switches that can't be turned on or off without physical contact by someone in the cockpit. The plane can't restore this power, only a person can flip the switches.

Removal of power to the motors prevents MCAS from being able to continue to add more nose-down trim. Unfortunately, most 737 pilots do not turn the trim adjustment wheels by hand when flying, because it is slow and awkward process. They usually use a small thumb joystick on the control yoke to adjust trim, which is carried out by the same electric motors used by MCAS. My guess is that with a bunch of nose-down trim, the pilots turned the power back on so they could make a large trim adjustment with the thumb joystick. But as the pilots add nose-up trim with the electric system, MCAS was again able to counteract that with nose-down trim.

Basically, MCAS can add so much nose-down trim, and do it so rapidly, that even disabling the system leaves the plane in such a nose-down trim that it is unrecoverable. The pilots can't crank the trim wheels fast enough by hand, and turning the electric motors back on gives MCAS the advantage again.

Re:Boeing Deserves to Pay for This

[Anonymous Coward]

Here is an article that states that when the jackscrew that adjusts the horizontal stabilizer is under load from aerodynamic pressure, the manual trim requires too much force to adjust trim. https://leehamnews.com/2019/04/03/et302-used-the-cut-out-switches-to-stop-mcas/

They turned the electric trim back on because the manual trim could not be used.

Authority

[Anonymous Coward]

The word "Report" has such an authoritative tone. According to the report...
And then you read who wrote the report. Of course they would conclude that their country, their people, their pilots were not at fault.
You see this legal positioning stuff play out over and over.

And all you can do is try to backpedal and say, no, the Ethiopian government isn't a reliable authority on the correct operation of a Boeing airplane. Then the argument goes to, well then who is?

BAD AD

[ghoul]

The AD which went out after the Lion Air Crash said disable the MCAS using cutoff switches. What it did not consider is that if the plane is already nose down then the aerodynamic forces are too strong to use the manual wheels to make it nose up. The AD should have specified use your electric trim yoke switches to make the trim up and then cut out the electric trim so MCAS cannot make it nose down again.
Also why is the MCAS triggering 6 minutes into a flight. Takeoff by definition is close to stall. It should be off during takeoff. If this plane cannot takeoff without MCAS then this plane is not safe. This is not a fighter jet where the pilot can eject if the software screws up or the plane goes unstable.

Re:BAD AD

[wired_parrot]

The AD which went out after the Lion Air Crash said disable the MCAS using cutoff switches. What it did not consider is that if the plane is already nose down then the aerodynamic forces are too strong to use the manual wheels to make it nose up. The AD should have specified use your electric trim yoke switches to make the trim up and then cut out the electric trim so MCAS cannot make it nose down again..

This is a good explanation of the difficulty in trimming the aircraft in a mistrim condition by a former senior Boeing engineer. The short of it is that in the mistrim condition encountered by ET302, with stab nose down and the pilots pulling elevator nose up, the combined tail loads would've produced high jackscrew load opposing nose stab up trim that would be impossible to overcome with manual trim.

Boeing did publish guidance for older 737 models on recovering on a severe nose out-of-trim condition, which would have required taking the aircraft into a roller-coaster maneuver to relieve the horizontal stabilizer loads. But given that they were already close to the ground, this was not an option. The other suggestion was to extend flaps, but given that the aircraft was above the minimum flap speeds, this was also not possible.

In short, it looks like the fix to the problem was as much to blame as the problem itself