The pilots know that the trim is moving, it's connected to a wheel in the cockpit that's super obvious.
But the normal way of stopping it (the yoke) doesn't necessarily work, and the pilots wouldn't necessarily think to physically stop the wheel with their hands.
This 3rd pilot was probably able to figure out the issue due to clarity of mind to not having to fly the plane, pay attention to all the instrument gauges while things are going wrong, trying to diagnosis and correct the issue.
Seems like pilots are overburdened by so much automation, as alluded to by the famous "Children of the Magenta" video[0].
I don't get why the plane doesn't just say what it's doing, and why it's doing it, and have a big red button to put the plane into a safe-mode alternate law. 737s already say warnings like "BANK ANGLE", couldn't it just say "DANGEROUS CLIMB DETECTED, TRIMMING NOSE DOWN. PRESS RED BUTTON TO CANCEL."
This is grossly overstating the optional feature. As I understand it, "AOA disagree" is a single light near the AoA indicator itself. It's not an explanation, or even an alert. It's not where anyone would reasonably look when trying to diagnose an uncommanded flight control problem.
The North American airlines bought it and no others did. It was not described as a safety feature -- if it was it wouldn't be permissible to make it optional.
Even the current training does not tell pilots to know that an AoA disagree light is an emergency because it can cause the plane to enter an uncommanded nosedive via MCAS. I really don't think it's reasonable to expect the pilots to know things that Boeing is not even trying to tell them.
> The Indonesia safety committee report said the plane had had multiple failures on previous flights and hadn’t been properly repaired.
It probably wouldn’t have mattered. Lion Air couldn’t even maintain their planes properly; assuming an extra indicator would help would be charitable at best.
But the normal way of stopping it (the yoke) doesn't necessarily work, and the pilots wouldn't necessarily think to physically stop the wheel with their hands.
Well, no. Pulling on the yoke traditionally moves the elevator. MCAS adjusts the horizontal stabilizer. You can adjust the stabilizer with switches on the yoke or with the trim wheels by your knee. MCAS will pause for five seconds if the pilot hits one of the switches on the yoke (and the Lion Air pilots did this until that stopped working).
I believe you may have misunderstood the comment you were replying to.
They were saying you cannot counteract MCAS's control inputs with the elevator alone. Which is a somewhat unconventional design, in a lot of aircraft the elevator can overpower the horizontal stabilizer, whereas with a bad sensor MCAS will continue to move the stabilizer until you cannot overcome it.
To use a bad analogy, in a car the break is stronger than the accelerator, so if the peddle sticks you can still stop. In other aircraft the elevator is more powerful than the horizontal stabilizer.
They were saying you cannot counteract MCAS's control inputs with the elevator alone.
Pulling on the yoke is not how you counteract a runaway stabilizer on the 737. I've pasted the relevant part of the QRH in a few previous comments. Yes, the stabilizer ultimately has more pitch authority under some circumstances. That may be what happened here, but if I'm interpreting the graphs on the preliminary report correctly I wonder about mechanical failure of some sort.
This gets a bit more complex with the 737 because moving the yoke WILL actually stop one of the stabilizer trim algorithms, but not MCAS.
> Pulling on the yoke is not how you counteract a runaway stabilizer on the 737. I've pasted the relevant part of the QRH in a few previous comments.
It is how pilots learn to counteract nose down day one of pilot training. In many aircraft hard elevation will overpower even a faulty horizontal stabilizer. If the QRH was a panacea we would have 348 fewer loses today.
> That may be what happened here, but if I'm interpreting the graphs on the preliminary report correctly I wonder about mechanical failure of some sort.
There was a mechanical failure, the AoA sensor. I'm skeptical there needs to be more going on than MCAS due to the "repeated correction" unauthorized change Boeing made.
> “The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”
In many aircraft hard elevation will overpower even a faulty horizontal stabilizer
In the 737 you can get into situations where the elevator has insufficient authority to overcome a stabilizer. Excessive pitch up (leading to a potential stall) that you can't counter by pushing on the yoke is exactly what MCAS is designed to prevent.
There was a mechanical failure, the AoA sensor.
A fixed offset from reality is an interesting failure mode, especially in two separate sensors (Lion Air replaced the alpha vane before flight 610), and even more interesting as it's the same alpha vane used in the 737 NG. The left alpha vane was being interpreted as almost exactly twenty degrees higher than the right.
The left alpha vane was being interpreted as almost exactly twenty degrees higher than the right.
Is that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount
I think it's been disclosed that in Lion Air the sensors were twenty degrees apart even when sitting on the runway before the flight. It is shocking that nothing checked for disagreement or communicated it to the pilots.
Is that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount
The difference in angle of attack was consistent throughout the entire flight (well up until the crash where the values began to converge). The threshold for the optional 'angle-of-attack disagree' warning is, I think, ten degrees. It seems very unlikely that the plane had a twenty degree bank angle for two entire flights.
But the normal way of stopping it (the yoke) doesn't necessarily work, and the pilots wouldn't necessarily think to physically stop the wheel with their hands.