Boeing 747-400: Why does the plane lurch forward when AP is activated?

Basically the title. Whenever I activate the AutoPilot, the nose of the plane drops suddenly and then rises again and repeats, each time a little less extreme until the plane flies on a steady line. Does anyone know what I’m doing wrong?

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Trim your airplane. The AP probably had to pull back to make the plane level. If you trim up a bit so the yoke is on a neutral position, this will not happen. It’s something I need to fix though…


230 at which altitude? No need for flaps at those speeds.

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I find it helps a little bit to not set the A/P until I’ve reached a steady manual climb rate after I’ve climbed above FL100. Can’t really avoid it completely though at the moment.

Yeah, I realised that was wrong after posting it. I didn’t have IF open and was trying to remember the various flight values. I should have known I wasn’t flying at 230kts with flaps at 20, the plane would have been travelling horizontally with the nose down xD My bad.

Thank-you, I’ll give that a try. I did originally try to set the climb rate just after take off and then manually raise the nose gently until the climb rate matched the one I’d already set. Then I’d quickly activate AP so the set climb rate and the climb rate at the time of AP activation were the same (hoping for a seemless transition) but it still just suddenly dived forward. Thanks again :smile:

Adjusting the trim didn’t fix anything. I know it is a bug now, because the exact same thing happens if you’re viewing a departure in the replay, and the autopilot has been engaged, when you click ‘LIVE’ to jump into that part of the replay. Even with the AP already controlling the plane! Good luck fixing this one I suppose.

I tend to take the 744 off with flaps 20 once in the Air and about 230kts flaps 10 trim +10 and the auto pilot engages smoothly. I also think too steep a climb rate does not help on such a heavy old girl!

This happens with multiple aircraft, and sometimes it goes to the point where the autopilot disengages and I usually crash.