777 300ER and A321 autopilot problem

Hi guys, this is the second time now, getting annoyed.
Am flying now 777 with 72%load, cruise 33000ft M 0.78 winds 25knots.
The plane can’t be stable as the autopilot is trying to maintain at 33000ft… so the pitch will go up and down with -400 and +400 vertical speed difference.
Have tried reenganged the AP but still.

Only have issue with 777 other planes are fine.
I know this topic have been discussed before.

Thank u


What I found when this happens is that my speed is usually to low so I would recommend a speed of .80-.85 at 33,000ft-37,000ft


You need to stepclimb. Use simbrief for help to know when to stepclimb, it is also very great for other stuff. When you are too heavy and you go higher up, your aircraft doesn’t get enough air to creat lift, so it almost stalls. You should start at a low altitude, and climb as your weight drops.

Oh and just like @Daniel14 said, you should go a bit faster, you could use simbrief for that too!


That’s kinda fast, usually in real life they fly between 0.77 to 0.80 M at that cruise alttitude… is just only this model of aircraft does…sigh

Yo! Have tried that too, was M 0.84… still up and down…

I’m currently doing my second ULH with the 777-300ER as I type this and haven’t encountered any issues of this sort. The standard cruising speed for the 77W is Mach .84. Since you’re going too slow at a relatively heavy weight at a relatively high altitude, the autopilot struggles to maintain balance. Increasing your speed should solve this.


Maybe you are just too heavy, try to descent and see if it helps. If it does, you should probably start there and stepclimb as your fuel burns.

Hm as I said. I did try to speed up to see if it changes, but nothing…

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Hmm. What is your trim at? Is a purple line visible?
Even shortly into a flight at heavy loads I haven’t encountered this.

Trim 0
They have experienced this before, and the staff said nothing we can do.
Everyone has different experience

The trim is most definintely the issue. Even at light weights near the end of a flight in a 77W, I have 25-30% positive trim. Early on/heavy you should be at around 40-45% positive trim.

Congratulations you have noticed your aircraft going through a thing called turbulence.


So what should I do now? Trim to 30-40?

Ehmm I am sure it’s not.

It’s just not the trim problem.
Is the setting itself have some issue with it

And can you provide evidence that it is not. For example I had mine bobbing up ant down from 1000fpm to -1000fpm caused by turbulence. I have done over 30 flights in the B77W and not once have run across this. This is merely a repeated problem of people either not operating the aircraft properly or not being able to notice turbulence.


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cruise anywhere from m.83 to m.86 with the 777, you are going too slow.

Criticism is warranted when one denies the answer that has been given time and time again and for one who cant seem to use the search function for the more than enough times this so called “problem” has been created on this forum.


That is correct. I’m pretty sure every pilot on here knows what turbulence is, therefore it was pretty unnecessary.