New York Times article:
The article isn’t completely accurate. Doing nothing for 40 seconds in any airplane would have been a serious problem if it was nosing over.
The crew would need to shut off the MCAS system but the logical solution would be to trim neutral with the normal electric trim and THEN shut off the MCAS. assuming they knew how to do it. As long as the electric trim worked they could play trim tag to the next airport. They should have recognized the time interval involved when the MCAS kicked back in.
I have to wonder if there wasn’t a secondary issue that, when combined, made the situation much worse.
I don’t think the article is suggesting 40 seconds of doing nothing at all, just 40 seconds without trimming or disconnecting the electric trim, you’d still be pulling back on the control column.
The secondary issue was probably just that they had no idea MCAS existed or what it did and why it did it. It’s obviously not an insta-death fault because the previous crew dealt with it satisfactorily with the help of someone in the jump seat. It’s not surprising the jump seater was useful, you pick up a lot more when you can sit back and take in the big picture.
wouldn’t you see the trim wheel spinning on it’s own and figure out it’s a powered-trim issue?
At some point while pulling back on the yoke it should be obvious the tail plane is trimming itself.
Here’s some anecdotal analysis from a 737 pilot who thinks it might not have been that obvious of a situation: Ethiopian airliner down in Africa - Page 102 - PPRuNe Forums
An interesting read except for the first sentence is a bit of a straw man:“Oh, they should have recognized it immediately and disconnected the trim:”
I think the repeated engagement of the MCAS to be more obvious then initial input by the system.
plane noses down, pilot pulls back and retrims. plane noses down, pilot pulls back and retrims. plane noses down pilot pulls back and retrims…At some point the trim system should enter the thought process because that is what the pilot is fighting against.
Keep in mind all this is speculation until the black box data becomes public. Assumptions are being made as to what the MCAS system normally does and not what transpired in either of the accidents.
**Latest black box data **emerging from the Ethiopian crash seems to confirm that a faulty AOA sensor and MCAS were the cause, as everybody has been guessing.
New York Times:
In Ethiopia Crash, Faulty Sensor on Boeing 737 Max Is Suspected
Sydney Morning Herald:
Investigators find first hard link between the two 737 MAX disasters
Longer read, about how it happened:
Given Boeing’s bad PR at the moment, wonder if this would be a good time for an airline who still has faith in the 737 MAX to place orders for some MAXs at a discount that wouldn’t be given under normal circumstances - if Boeing would agree to it.
Looks like the pilots did turn off the MCAS, but it came on again (it is not sure if they turned it on again or it came on again automatically)
Brian
Talk about a big difference in liability for Boeing between those two options!
If you couldn’t shut the system off that would be a huge problem.
There’s a real lack of clarity about exactly what was “turned off”. The implication that they followed the exact procedure in the Boeing and FAA bulletins and it still didn’t help is certainly disturbing, but it’s as likely as not to be merely confused reporting based on an unofficial leak. Which is why it’s important to wait for at least the preliminary report. It seems hard to believe that physical switches cutting off both primary and backup power to the electric stabilizer trim could fail to disable the MCAS. Something seems wrong with the set of facts being reported here.
Possible bird strike:
Perhaps switching off the stabilizer did disable the MCAS, but they still couldn’t pull out the dive with the stabilizer switched off, so they had to try switching it on again.
From the preliminary report, you can see that after they flipped the stabilizer cutout switches, the MCAS sent an AND (aircraft nose down) signal, but the stabilizer did not move. So it looks like the switches worked to disable MCAS control of the stabilizer. But those switches cut all electric control of the stabilizer.
According to the cockpit voice recording (CVR), the copilot tried to adjust the stabilizer manually, but was unable to move it using the manual wheel. It is possible that the forces on the stabilizer were too great for one person to be able to move it by hand. After that, there are powered stabilizer movements in the ANU direction from the switches on the control yoke. One explanation is that the cutout switches were flipped back on so that powered adjustments could be made. 5 seconds later, MCAS activated again and moved the stabilizer in the AND direction again for the final time.
At that point the control yoke forces may have been too much to hold back, because the airplane was going 500 knots, and wound up hitting the ground at 40° nose down.
It looks like the pilots carried out the “correct” procedure, but could not recover control of the aircraft in the time and altitude that they had to work with. If they had been much higher, they might have had room to reduce the forces on the stabilizer by letting the plane pitch down, and then manually crank the stabilizer back up. But it was not a procedure that could work with the problem happening so close to takeoff.
The preliminary report also has some odd additional data, like the fact that there was a roll oscillation, which had occurred before. And the AoA sensor data looks different from the problem in the Lion Air crash. This one looks more like an electrical problem. The Lion Air one was consistently off by 20°, almost like a calibration error. This one jumps around and also pegs at 75° with no variation for awhile, and then jumps around again.
The correct procedure for what problem?
I suggest you actually read the Preliminary Report, then you’ll be in a better position to comment.
Also being discussed in this GQ thread.
The issue appears to have been not so much yoke forces as the inability to operate the manual trim wheels in that overspeed situation due to the aerodynamic forces on the horizontal stabilizer trim. It didn’t reach 500 kts until near the end but the overspeed warnings were already sounding during most of the time they were trying to correct the problem (I believe maximum indicated airspeed (IAS) is about 340 kts). You’re right that more altitude would have given them an opportunity to electrically move the stabilizer to a more neutral position before activating the STAB CUT-OFF switches, and in fact there is a “yo-yo” procedure to achieve this, but they had no opportunity. The fact that the pilots appeared to follow the exact procedure set out in the Boeing flight operations bulletin after the Lion Air accident was absolutely damning for Boeing.
The emerging picture here is that Boeing’s single-minded quest to push the 737 MAX as virtually identical to previous generations and requiring essentially no pilot retraining led to some design decisions that in hindsight seem extremely irresponsible, to an extent that is now implicating the FAA as well, and the whole question of regulatory oversight. One was to design the MCAS software to use the input from only one angle of attack sensor even though two are present (ostensibly to avoid procedures for dealing with disagreement), another was to make AOA readings or even a warning about disagreement between the sensors optional extras, and a third was a failure to thoroughly document contingencies for dealing with MCAS problems, or indeed to document the MCAS at all. One flight manual for the 737 MAX obtained by the media has the term “MCAS” in the glossary, but no mention of it anywhere else in the manual, suggesting it had once been mentioned or described but the reference had subsequently been edited out.
Boeing in fact boasted about how quickly the 737 MAX was brought to market and how identical it was to previous generations so that essentially no pilot retraining was required. Now, as it were, the chickens have come home to roost. After the Ethiopian preliminary report, the Boeing CEO had no alternative but to admit to a design fault, saying simply “we own [this problem], and we know how to fix it”. I have no doubt that the fix will be robust, but as far as the original design decisions are concerned, the word that comes to mind is “unconscionable”.
The insuinuatioms that Boeing happily placed in the web post crashes that non-white crews were somehow too stupid to fly the planes did not help either.