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In reading about various theories of what happened to flight MH370, there's a lot of discussion about it possibly crashing into the ocean, breaking up, and pieces of the aircraft floating hundreds of miles away.

Is it generally expected that large pieces of an aircraft will float fairly well? E.g. in the linked article, there's a picture of 4 guys carrying what looks like a big chunk of wing. How did that float?

My assumption would have been that that chunk was hollow aluminum fuselage, maybe with some electronics and hydraulics inside, and maybe a portion of a gas tank. I don't get how it would float unless it got lucky and a subsection of gas tank that was empty and did not get pierced during the breakup landed with its inlet/outlet pointing up.

Thanks.

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    $\begingroup$ It's important to remember that water is actually very dense. 1 kg/L or 8.3 lb/gal. As a result, lots of things float, Jet-A included. $\endgroup$ – reirab Mar 22 '18 at 20:11
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    $\begingroup$ Have you heard about these things called "ships"? They are typically made of steel, which is much heavier than aluminium. Apparently, they float pretty well. $\endgroup$ – Jörg W Mittag Mar 23 '18 at 0:11
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    $\begingroup$ @JörgWMittag: Only by the virtue of careful engineering and by being the right side up: break them into random chunks (which is the case discussed here), or even flip them sideways, and they'll sink like bricks. $\endgroup$ – Piskvor Mar 23 '18 at 9:32
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    $\begingroup$ @JörgWMittag As I clearly stated in my question, I'm curious about broken up chunks floating, where I would picture them not being water tight, and therefore not being able to displace their entire equivalent volume in water, which is the effect on which metal-hulled ships rely to float. $\endgroup$ – SSilk Mar 23 '18 at 13:18
  • $\begingroup$ Parts of MH370 that have been found floating have been sections of flap and other control surfaces and cargo or pax doors and hatches. They are frequently all but sealed sections of the airframe, perhaps with breather holes to allow pressure equalisation but if they are in water with breathers down very little gets in. Airframes are also extensively treated with sealants inside to prevent oxidisation so even a couple of years in seawater does not do them too much harm. Large tanks are not found as they are usually simply sealed parts of the airframe that break up on impact. $\endgroup$ – nimbusgb Mar 26 '18 at 7:26
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Lighter materials such as plastic will naturally float.

Composites can have large sections of honeycomb core with trapped air. Even if these parts are broken, the honeycomb is sealed against both sides of the panel, still trapping air.

Large sections, whether made from composite or metal, will generally be hollow to save weight, and sealed to prevent collecting moisture which could cause corrosion. There may be small drain holes, but they wouldn't be enough to cause significant leaks.

Fuel tanks are sealed but they are also fairly large and contain baffles to allow fuel to flow within the tank. As you would guess, a catastrophic crash would be unlikely to leave a significant portion that doesn't contain holes.

The parts found suspected to be from MH370 all have these qualities.

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