[shirro]

I don't know if this is practical or not. Have two or more compartments on a plane filled with dozens of small highly reflective buoys. Each with some sort of radar reflector, either passive or active, that searchers could light up with radar and it would emit back a strong signal. In event of a breakup their container is designed to scatter them everywhere or in a more controlled situation the planes systems could release them. Ofcourse they will drift in the air and in the ocean currents but you could analyse then statistically along with knowledge of wind and ocean currents to at least narrow the search area in a situation like this one.