How the MH370 Flaperon Floated

[mralstoner]

Couldn't something float yet be submerged if it had air trapped in it?

I don't know how these flaperons are constructed. Might they have some buoyancy from trapped air?

I think the problem is that an object is very unlikely to exactly match the buoyancy/weight of water:

“It is very hard to build something that will float slightly below the surface,” wrote David Griffin, an oceanographer with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), in an email. “The probability that an aircraft part does this is miniscule. The only way it can do this is if some of the object breaks the surface. If it does not break the surface AT ALL it must sink.”

As for the flaperon materials:

The upper and lower surfaces of 777 flaperon are “made of  honeycombed composite – presumably carbon fiber” while “the leading edge is mainly made from high tensile aluminum (2024-T3) apart from the fibreglass doubler.”4 As a general rule, things made of composite material exhibit excellent buoyancy. The honeycomb materials which makes up most of the volume of the composite skin weighs only about 5 percent as much as water.5 Composite aircraft parts, therefore, tend to float fairly high in the water,

Yes, air could presumably be trapped in the honeycomb, although they say the honeycomb would crumble/collapse at deep sea levels.

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