Inside manned sub: Sifting through underwater debris

The underwater drone in search of Malaysia Airlines Flight 370 wreckage has begun its ninth mission.

So far, the Bluefin-21 has scanned about two-thirds of the intended territory without finding any sign of the missing plane.

Oceanic salvage manager: How we search for Flight 370

If any debris is found, the next step could be a manned mission to sift through potentially hundreds of tons of wreckage on the ocean floor.

CNN's David Mattingly is inside a manned submersible to takes us through the process of cutting through debris to get to an aircraft's black box.