Maybe time was an issue? Saw in an earlier post that the issue had to be mitigated within 40 seconds of it occurring.
All of those are “above the line, memory items” which the crew must be able to recall and execute prior to referencing the checklists in the QRH.
Boeing has some significant fault here, but I’d expect a full performance crew to handle this emergency and suspect the CVR and FDR data will show them in a less than fully flattering light, especially after Lion Air, the emergency AD, safety memos, and general publicity surrounding the previous crash.
Has the information disclosed to pilots after the LyonAir incident been made public?
What I have gathered from reading other forums about this, many pilots say they would interpret any significant undesired trim as a runaway condition, regardless of whether it was happening in intervals or it was literally continuous.
Others say that depending on training, and the policies of the operator, a much more literal reading of procedures is enforced.
I don't fly, but apparently trim is a very fundamental control for a pilot. It's easy to recognize when the aircraft is out of trim, and reacting to it is about as natural as it is for a driver of a car to use the steering wheel to keep the car centered in a lane.
So my assumption is, that with the AoA disagreement, and resulting multiple alerts and chaos in the cockpit, the pilots lost awareness of what the trim was doing.
I'm wondering if there's not a deeper problem within the air data systems. Why are the AoA sensors on new aircraft failing? They are just simple vanes, normally very reliable. The same ones are used on many different aircraft. So I don't think the actual sensor is a problem. But maybe there's something different downstream of the sensor itself. I would think if there were persistent problems with bad AoA data in 737s generally, it would have been addressed. Because the stick shakers, unreliable air speed, and everything else would still be happening regardless of MCAS.
This is a very good point. If the AoA sensor failed say climbing through cloud at 5000ft on auto-pilot, dropping control of the aircraft to a pilot who's busy thinking about what he's going to have for lunch, with half a dozen alerts going off, an AF447 type incident could easily happen MCAS or no MCAS.
If I've read correctly, the former only temporarily disengages MCAS. The pilots may have repeatedly hit the button on the stick, but then 20s later, MCAS re-engages and sends the plane nose down again.
I agree that the procedure calls for flipping the switch on the panel. But, not sure that's actually what the pilots were doing.
In the image below, you can see the electric trim control on the stick in the left portion, and the manual trim cut-out switch on the panel in the top right.
https://theaircurrent.com/wp-content/uploads/2018/11/737-max...
When this situation happens, five things happen at once. MASTER CAUTION (whoop, whoop noises and a big red light!), ALT DISAGREE alert on the MFD, Incorrect Airspeed on the MFD, the stick shaker goes off, and by the way, if you take the time to look down at the throttle section of the dashboard with all those other alerts going off, you'd see that there is suddenly a lot of trim on the APL trim indicator but the trim wheel doesn't actually move (which would provide an audible 'click click click' that would probably trigger that there was a problem with trim.
Each of those things has a separate memory checklist that you have to run down, and subtract ten seconds to register them, prioritize, communicate with the other pilot, and start executing them.
The worst part here is that they've added another alert and then changed how the airplane will fly in the middle of an emergency. While the extra alert narrows down the number of branches from the "prioritization" part of the checklist, I'm not sure that's "fixing" the problem.
I appreciate your point about all of the alerts going off however the pilot is manually flying the aircraft at this point, they should feel that something is going on through the controls and react to that firstly. Imagine having a blow-out in a fancy car with pressure sensors, sure lots of alerts are going off but you have probably not registered that because keeping the car going in a straight line is taking 100% of your attention.
Otherwise, yes I agree. A lot of stuff probably went crazy in a short time for them.
In all those cases, your reaction is the same and instinctive regardless of whether or not you know the root cause.
Flying an airplane manually on instruments, the pilot sees the airplane undershooting the pitch target and pulls back on the control column every bit as naturally as the car driver above. When the pitch target is correct and the control force high, use the stab trim to take the force away. This is every bit as much a continual process as the driver lane keeping.
If MCAS is trimming against you every time you let go of the trim, you get feedback that this is likely a trim issue. Keep flying the airplane and trimming as needed.
This is not a case where the airplane automation fails and an airplane suddenly gets “dumped” onto a pilot who has to regain control and figure things out.
It’s obvious that the time and space available was not enough for that Lion Air or that Ethiopian Air flight, so you have real world evidence to support your point. I acknowledge that fact, of course.
http://www.b737.org.uk/images/throttlequadrant.jpg
See the scale with "APL NOSE UP" and "APL NOSE DOWN" next to the trim wheels.
Whether the pilots noticed it (or the attitude indicator pointing nose-down, or the rapidly decreasing altimeter...) is the question.
https://www.flightradar24.com/blog/wp-content/uploads/2018/1...
I've put the relevant figure showing the trim adjustments here:
Think professional developers (granted the bar is infinitely lower). You would assume no one would introduce a SQL injection vulnerability in new code given all we know and all that happened. Well...
Also some commercial pilot on HN provided another element of answer. When you are in an emergency situation, you don't have the time to sit back and think, you revert to experience, muscle memory and training. Even if it may have crossed these guys mind that it was the same problem than Lion air, they may not necessarily know the procedure to fix it while trying to keep the plane from crashing at the same time.
Just speculating.
- unreliable airspeed warning
- stick shaker (=stall is imminent)
So you don't know your airspeed (otherwise you can conclude you're safe for your current pitch and vertical speed) and a stall warning. The last thing you do is to look for horizontal trim.
You can see them in the Lion Air preliminary report linked above.
Pilots are trained to deal with partial panel situations. The mantra is pitch + power = performance. In VMC this should be well within the capibilities of a normal pilot, put the nose on the horizon and set something like 65% power.
Not true. From what I have read, MCAS runs in 10 second intervals, with the amount of trim added increasing with each successive run. Once the trim has reached a certain point, it over-powers the amount of control the pilot has by putting pressure on the yoke (this controls elevators, which have less overall influence on the aircraft than the trim at full bore).
We know that the pilots on the previous flight with the 3rd deadheading pilot were attempting to right the plane using yoke pressure, and at one point the first officer mentioned that the yoke was "too heavy to hold back". That indicates that MCAS had pushed the trim past the point at which the pilots could physically overcome it's influence using the elevators. (source here: https://www.reuters.com/article/us-ethiopia-airplane-regulat...)
For some reason before the crash the pattern of repeatedly correcting changes, possibly because he handed control to the first officer.
It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke. "
So, yes and no. It gives SOME control over the trim, but if the trim keeps getting bumpped progressively higher by the MCAS, it will eventually outstrip the yoke control.
My guess is that that change you mentioned is the threshold at which their yoke trim control became insufficient.
They are saying there that near Vmo (maximum operating speed) with an aft centre of gravity (the aircraft loaded in a specific way) there might not be enough nose down trim authority available within the limits of the electric trim to completely trim the aircraft (allow the pilot to relax the forward pressure on the yoke).
In the crashes there was too much nose down trim and MCAS kept adding it more. They are trying to move it in the other direction.
Pants reporting but nothing to see here.
> there might not be enough nose down trim
After reading it, I'm not sure how you are gathering that it's only nose down trim. It only mentions an inability to completely set the trim longitudinally. Longitudinal doesn't mean in one direction. It only indicates which plane we are talking about, which in this case is pitch.
> Vmo (maximum operating speed) with an aft centre of gravity (the aircraft loaded in a specific way)
"The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts"
The issue mentions that there are certain corners, and lists what you posted after e.g. That isn't the only corner case in which the yoke trim control becomes insufficient.
Further, the section on EUSA's position clarifies that they wanted to improve the margin of safety on an out of trim dive, this is where 3 seconds of nose down trim (incidentally, that's how long they expect it to take for a mediocre pilot to identify a trim runaway) are applied without pilot intervention and the pilot has to demonstrate controllability.
But that point is pretty moot because the electronic trim cannot drive the jackscrew to the extremes that the manual trim wheel can, but it can return from the extremes to the centre. MCAS is driving trim to the nose-down extreme and the pilot is trying to return it to neutral.