787 now has a bug that takes total control of the elevator trim even when not in autopilot

User Support Hub Aircraft & Systems
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I’m the developer of the 787’s fly-by-wire system so I am aware of how it operates, yes. :slight_smile:

I’m just trying to be super clear, since folks often misunderstand what using the system means. You are correct in that just like a conventional controls aircraft, once you trim the aircraft for a particular attitude and speed, if you do not change the attitude or speed of the aircraft, then you will not require trim changes.

However, your statement could also be read as “once you trim the aircraft to your speed one time, then you won’t have to trim again in the future as the system will trim to any future speeds for you”, which I want to make sure people don’t take as the case. The trim operation on Boeing fly-by-wire systems is intended to work exactly like conventional controls: you can trim for one speed, but if your speed changes at all, you must adjust your trim to maintain your attitude.

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That’s indeed a fair comment :slight_smile:

#Respect :slight_smile:

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This bug has disappeared after I did a hard boot and cleaned out my keyboard and joystick buttons. It had only appeared for a few days and then went away. Also, the Auto throttle is working on the 787 again. Good thing I didn’t send in a bug report on it yet. No need to shut down an engine to slow the speed down. Strange that even with autothrottle off I hadn’t been able to slow the aircraft down with the speedbrake on or off.

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Yes, that is how I found that it was working . I wasn’t sure of the algorithms used but I had noted the response on the elevator at different speeds. I have done some real world programming on marine autopilots (in machine code for microcontrollers ).. But the rest was just a gray area as to what logic was used to make the elevator behave as it had been.

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