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Am I mistaken or is there a missing item in the chronology where the pilots reactivated the electric stabilizer trim? The timeline mentions stab trim being swi

Am I mistaken or is there a missing item in the chronology where the pilots reactivated the electric stabilizer trim? The timeline mentions stab trim being switched to cutout, and if you look at the FDR graphs there's a (relatively) long period of more-or-less stable trim after that. But then there's an automatic trim down, which is only possible if the electric stab trim is switched back on, and there's no mention of that. I also can't help but wonder if exceeding Vmo was a factor. (I don't mean to sound as though I'm trying to assign any blame here. Obviously this was a confluence of problems, the most significant of which is the control system reacting to an erroneous 75° (!) AOA indication.)

VBprogrammer 8y ago
The graphs record the AND trim movement even if the electric trim is disabled. You can see that by comparing the pitch trim absolute position to the manual and automatic electronic trim graphs.
- danaliv 8y ago
  Right, I get that, but the last automatic AND actually moved the stabilizer.
  - VBprogrammer 8y ago
    Your right. They didn't mention it, probably because it's not indicated on the CVR at what point they decided to try turning it back on.
phire 8y ago
The pilots didn't make verbal mention of re-enabling the switches and the position of the switches isn't recorded in the flight data recorder. We have no way of knowing when, or why those switches were flipped.
Torquer 8y ago
I find it amazing that there is no mention in the report of this fact. The investigators obviously know that they turned the cutout switches back to normal mode. Assuming there really was no mention of it on the CVR strongly suggests that it was the very inexperienced first officer who did this (the switches are on his side) without getting concurrence from the captain. If you carefully study the graphs in the report, the plane was really not in bad shape up until this point. They were 7000 feet above ground and climbing. They were going too fast, but again, this is the fault of the crew. If they would have not flipped the cutout switch and taken stock in the situation and backed the throttles down, it is quite possible this flight would have ended very differently.
- guyhg 8y ago
  There are a lot of well-taken comments in this thread. However, in reading the Lion crash report and this one, it strikes me that there is a fundamental difference in the crashes. In this case, it appears that the pilots had very little knowledge about the reasons why the anti-stall system was implemented. And their combined flight time on the MAX is absolutely pitiful. In short, normally one thinks of a stall as a low speed event. In this case, by switching to manual with an improperly trimmed plane, it began a process which could be magnified by an accelerated turn (one of the reasons the MACS exists in the first place.) They began executing a rapid 180 degree turn at >300 knots, which is shown on the attitude graph, headed back to the airport. With a heavily loaded plane, is there any reason to doubt this wouldn't induce a high speed stall? The plane became so unstable, as it was outside of its operating envelope, they could not manually trim it. When they used electric trim it turned the anti-stall system back on, and it nose-dived the plane. The Boeing manual and/or directive says once you turn it off, it stays off. If they were unable to manually trim, is it really much of a surprise given their airspeed and rapid turn? So you ultimately see an electric trim which did little to help them, and assured anti-stall would kick in again. The report shows that neither of the pilots had signifcant experience in the MAX. The CVR is replete with ignored overspeed warnings, and stall warnings. An experienced pilot would know the danger is not a low speed stall, but a high speed stall accelerated by a mismanaged turn. By the time they tried to electrically trim it, it was over. Many planes are not aerodynamically stable without computer assistance. This crash is far different from the Lion crash. And I have not seen a single news outlet state the conclusions (or lack thereof) in the report accurately.

VBprogrammer 8y ago

The graphs record the AND trim movement even if the electric trim is disabled. You can see that by comparing the pitch trim absolute position to the manual and automatic electronic trim graphs.

danaliv 8y ago
Right, I get that, but the last automatic AND actually moved the stabilizer.
- VBprogrammer 8y ago
  Your right. They didn't mention it, probably because it's not indicated on the CVR at what point they decided to try turning it back on.

phire 8y ago

The pilots didn't make verbal mention of re-enabling the switches and the position of the switches isn't recorded in the flight data recorder. We have no way of knowing when, or why those switches were flipped.

Torquer 8y ago

I find it amazing that there is no mention in the report of this fact. The investigators obviously know that they turned the cutout switches back to normal mode. Assuming there really was no mention of it on the CVR strongly suggests that it was the very inexperienced first officer who did this (the switches are on his side) without getting concurrence from the captain. If you carefully study the graphs in the report, the plane was really not in bad shape up until this point. They were 7000 feet above ground and climbing. They were going too fast, but again, this is the fault of the crew. If they would have not flipped the cutout switch and taken stock in the situation and backed the throttles down, it is quite possible this flight would have ended very differently.

guyhg 8y ago
There are a lot of well-taken comments in this thread. However, in reading the Lion crash report and this one, it strikes me that there is a fundamental difference in the crashes. In this case, it appears that the pilots had very little knowledge about the reasons why the anti-stall system was implemented. And their combined flight time on the MAX is absolutely pitiful. In short, normally one thinks of a stall as a low speed event. In this case, by switching to manual with an improperly trimmed plane, it began a process which could be magnified by an accelerated turn (one of the reasons the MACS exists in the first place.) They began executing a rapid 180 degree turn at >300 knots, which is shown on the attitude graph, headed back to the airport. With a heavily loaded plane, is there any reason to doubt this wouldn't induce a high speed stall? The plane became so unstable, as it was outside of its operating envelope, they could not manually trim it. When they used electric trim it turned the anti-stall system back on, and it nose-dived the plane. The Boeing manual and/or directive says once you turn it off, it stays off. If they were unable to manually trim, is it really much of a surprise given their airspeed and rapid turn? So you ultimately see an electric trim which did little to help them, and assured anti-stall would kick in again. The report shows that neither of the pilots had signifcant experience in the MAX. The CVR is replete with ignored overspeed warnings, and stall warnings. An experienced pilot would know the danger is not a low speed stall, but a high speed stall accelerated by a mismanaged turn. By the time they tried to electrically trim it, it was over. Many planes are not aerodynamically stable without computer assistance. This crash is far different from the Lion crash. And I have not seen a single news outlet state the conclusions (or lack thereof) in the report accurately.