I'm curious why the system would be allowed to cause "uncommanded horizontal stabilizer trim movement" when the data are known (or suspected) by the system to be erroneous. Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?
I really want to know what can cause the STS nosedown trim in unreliable airspeed... Toxic data from ADR? or?
Not familiar with the setup...
Yes they were. I feel a lot will be revealed on the CVR. Not arm chairing, just extremely interested to hear the CRM during this tragic loss of life.
I'm sure a LOT would be revealed, including CRM deficiencies... and a lot of arm chairing too by many others.
I’m reading a lot of of they should have done this or that and flying the airplane with full trim up or down is easy, let’s stop right there; they may be designed to work that way but it ain’t easy in the least bit. It would take an incredible amount of control force it to hold an airplane level with full trim down or up. And yes there are procedures to disconnect a runaway trim wheel, but if the pilots were getting false info, they might have been focused on that and not noticed the trim right away. Should they have been able to recover from this? Probably. Should it have been easy? Hell no
Agree... on their own, UAS or runaway trim, should be a "no sweat"... but as a combo? I think it's a different story altogether... If it was easy, the bulletin wouldn't end up with an EAD on top of it.
Speed Trim System works to return the aircraft to trimmed airspeed. It takes inputs from throttle position, stabilizer position, airspeed, and vertical speed. When the airspeed deviates from the trimmed airspeed the STS moves the stabilizer to return the aircraft to the trimmed airspeed. This means the aircraft will climb or descend until the trimmed airspeed is reached, at which point the STS moves the stabilizer back to the trimmed position (reduced control forces).
Does this mean STS would be allowed to take in toxic data from the ADR? If so, I wonder there isn't a way to stop STS from taking toxic data in the event of an ADR fault or unreliable airspeed? To me sounds like asking uncessary workload during unreliable airspeed.
(Of course, hindsight, is always 20/20)
This is particularly true of the speed trim system, which has expanded authority beyond that available to the NG variants to activate during manual flight – this is because of differences in the longitudinal stability of the 737 MAX.
I hereby declare that I hate the new Boeing FCOMs that don't explain the systems in detail unlike the days of the 737-200 manuals. I hate this "it's under the hood, you don't need to know the details" kinda thing... Just a personal opinion...