How the MH370 Flaperon Floated

[mralstoner]

But still, floating while submerged sounds unlikely. More likely it was tethered beneath the surface somehow.

What sort of tech would that involve in 5000m waters?

That's the point. Tethering to the seabed at 5000m is unlikely (or impossible because: the honeycomb would collapse and sink it; and because the barnacles don't grow that deep). Tethered in a shallow grave is possible, but doesn't fit with the satellite data. Hence human intervention (foul play) starts to look more likely i.e. it was tethered in the perp's laboratory.