777-300ER Unable to hold Altitude

Hi, I’ve been having this problem for a while. The 777-300ER won’t hold its altitude and keeps pitching up and pitching down all of the time, it’s only the 300ER with this problem.


Looks like you were at Mach 0.81, a bit too slow for the 77W.

I recommend speeding up to Mach 0.84 to make it a bit more stable.


Not sure how those help that issue.

You can try speeding up like @Thunderbolt said, although the 777 still shouldn’t have too many issues at that speed.
It may have been your VS up to FL400 may have been to high, so ~1000 VS should be fine.
If you want to fix it mid-flight, disengaging autopilot for a bit and reengaging may work, but keep your VS low when you reengage, and put your sensitivity to low so you don’t lose too much altitude.

Doing what you said will most likely not fix it.

He is on autopilot, so calibrating does nothing. Also, 2000 feet is not 34000, so it is probably different.

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Agreed, perhaps increasing the speed? Like you suggested @Thunderbolt?

Like suggested, increase to 0.84.

Also, what is the weight, onboard?

He probably has a light load, if you look at the throttle he’s handling FL400 without any difficulty

The 77W has this issue where it can’t stay at and altitude. Causes are too high of a vs on initial climb causing AP to pitch down more once you reach your altitude. Also too low of a speed can do it

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The 77W has a known issue where when ALT is enabled, the aircraft could bob up and down and not remain stable. Considering you’re at a reasonable altitude for your weight (based solely on fuel), I would suspect this is the case here. To fix this

  1. Turn off ALT once you reach your desired altitude
  2. Set V/S to 0 and leave it

This should make your flight more stable

I would also recommend accelerating to M .84 as this is the 777’s cruise speed. I hope this helps!

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Yeah I’ve tried changing speed but no change

What is your current altitude?

The thing is I’m not a light load and have tried different weights on many flight to see if it will resolve

Well I was at 34000 but this happens at all altitudes

What is your trim/flaps setting?

Well at 34000 ft , flaps UP and +12 trim

That’s very weird that you are having that problem, since I fly the 777 on the exact same settings.

After you land, do you mind uploading your replay to sharemyinfiniteflight.com?

Sure well right now I’m not in the air, i was only really testing to see if there was any change, but I will up load a reply of the flight

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Hi,@thunderbolt I’ve tried using the like you sent me but after I upload the video and it’s description, and then press submit it stops working and gives me no link, is there any other way of sharing the video ??

It takes some time to load.

Maybe the trim is causing that problem.