Boeing 777 "knocking" query

[wyrwb1]

Hi, I'm not technically qualified as aircraft go, but wonder is anyone canthrow a little light on a recent flight I was on.

The 777/300 had just taken off from Bangkok and I was sat over the wngs by the right hand side window. I found it rather disconcerting when,from below the floor, a heavy thumping could be felt. This would happen, three or four knocks, then stop for a while and then start again. this continuied to go on for about and hour into the flight then it stopped.
I brought this to the attention of the cabin crew, but felt I was rather fobbed off as nothing to be cocerned about.
Could anyone enlighten as to what the cause of this knocking could be. I know it's a long shot, but would be very interested to replies.

[PDR1]

An asylum seaker...

:O

PDR

[wyrwb1]

Funnily enough that thought did occur to me.

[PDR1]

I stress that this was a joke!

PDR

[wyrwb1]

Yes I realise that, but the thought really did occur to me.
i don’t know what is below that part of the floor and having 1000’s of miles to fly with the knocking, it was somewhat disconcerting.

[ShyTorque]

Maybe the co-pilot had locked the captain out of the cockpit.

[oldpax]

"About an hour into the flight"? Perhaps it was hydraulics being used until it reached the cruise when all systems should have settled down?

[wiggy]

Difficult to guess...

You do sometimes gets clunks if a cargo container is slightly lose in it’s locks so that would be a candidate if you were sat towards the trailing edge of the wing, but if you were further forward, e.g, very close around Door 3 on a -300 you are not above the holds, you are sat above major components of the air conditioning system, the centre wing fuel tank with it’s associated pumps, valves,plumbing etc, and the main gear bays. I’m not sure what is meant by the hydraulics settling down...there’s certainly a lot of hydraulic system action during gear retraction but after that no so much and a lot of the system associated with the gear is actually depressurised once the gear is sat in it’s uplocks.

[wyrwb1]

I was sat about 5 rows back from the door, pretty much just rear of the centre of the wing.
i don’t know if the pilot did anything or was even aware of the knocking, but strange that it stopped, never to reappear, after a couple of hours flight.

[spannersatcx]

recirc fans!

[wyrwb1]

This knocking was a “solid” thumping under the floor. Never experienced anything like it on any other flight and I have been on a few.

[wrenchalot]

There are a couple of possibilities; on most airplanes, the wings are attached to the fuse., by "male and females"
castings; a bushing goes across the hole and a close tolerance bolt attaches everything...
Years ago, we experienced the same issue, and finally they increased the tolerances between these parts , allowing them to "float": problem solved.

The other possibility is air in the hydraulic system; the banging can be quite alarming if you don't know the cause of it.

[Gibson9]

Lumps of ice in the mixing manifolds. Aircon would have been on high cold on the ground in Bangkok.

[wyrwb1]

Seems a good theory to me, although I have no idea what was below me. But, as I say, after a couple of hours there was no more bother.

[lochias]

most likely the center hydraulic system ADP to assist center hydraulic demand during take off

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/1071x800/777_hyd_7884b5ac6d473fa0c4b56a2b4588feb6ec8d277a.jpg

[wyrwb1]

Thanks for that all you guys. Very interesting to have more of an idea what’s going on down below and what could have been the knocking.