777-300ER Bobbing at cruise

Hi everybody, I’m sorry if there is already a topic on this. I looked and couldn’t find one identical to this. Currently, I am cruising at FL290 from KBOS to VHHH. My plane began bobbing slightly when I was on altitude hold, and I knew it would progress and get worse, so I switched to v/s mode and set it to 0 fpm. My plane is still slightly bobbing and I am afraid that if I leave my phone unattended, I might eventually stall and crash. Any ideas?

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There will always be slight fluctuations with your alt even with AP on, what are the winds like and how much is the altitude dropping/increasing?

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This should be in #support also you were most likely too heavy or going too fast.

This seems to be an old problem that pops up occasionally.

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It starts around 5 feet, then gradually increases. 38 kts right quartering tailwind.

Ok thank you.

Thank you, that was helpful!

Not really.

This is generally triggered on the A321 and the 777-300ER when slightly too “aggressive” vertical maneuvers, incorrect trim or speed is being used.

When i say aggressive, I don’t mean you’re treating it like a fighter. It usually means the V/S during climb might have been too much and when leveling off the AP overcompensates and are having troubles finding it’s way back.

Usually, adjusting the VS for the AP without altitude engaged does the trick.


Thank you!

Can you help me? I have tried all of this and it worked for a little bit. It is now getting pretty severe and I do not want to end my flight as I am already 4h+ in.

Good timing on your problem, take a look at this:

What trim setting do you recommend? I’m at Mach .8 at FL310

Trim it so the purple bar is not visible. The triple 7 performs better at Mach .83-85, so increasing your speed might also help.

Ok. I was at .83, but the other comments suggested slowing down.

How many degrees is the nose of your aircraft pitched up?

about 2 degrees

What about the weight of the plane, and any turbulence?

Load is 68%, 644,000 lbs. Slight turbulence, and a 45 kt crosswind

The only idea I have left is to increase your cruise altitude to FL330 or 350, you should be light enough to maintain that.

Ok, I’m planned to climb to FL330 soon, so I’ll do that. Thanks for the help.

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