Originally Posted by
deanm
...if the aircraft did end up relatively intact on the sea-bed & still containing the boxes, how might they be retrieved?
[1] Can any of the deep-submersible AUV/ROVs perform any kind of hull cutting activity?
[2] Can hoisting gear be remotely attached to any fuselage structure?
I have been involved (as an ICAO Annex 13 accredited representative) in the retrieval of a CVR from a commuter category aircraft that sunk in 600 meters of water.
It was a very simple process. The remote underwater vehicle operators are provided with an engineering drawing that shows where the recorder is mounted within the aircraft fuselage. They then navigate the ROV to that location. It is quite easy for the ROV to punch through the aluminum skin of the fuselage. Once that is done, the recorder can be fetched.
In the case of a very large fuselage such as a 777, if the recorder is not mounted proximate to the exterior skin, a hole can be cut in the fuselage by tools affixed to the ROV, and then one arm of the ROV can be inserted into the hole to fetch the recorder.
I was quite surprised to see the ROV operator on this particular mission simply grab onto the bulkhead that the recorder was attached to, and pull on it until a good size chunk of the bulkhead (including the recorder, attached to its mounting bracket) came free. The ROV operator then brought the chunk of bulkhead with the recorder mounted to it to a basket under the ROV, and then the whole ROV was brought to the surface.
I suppose the ROV operator could have just grabbed onto the cylindrical case of the recorder and ripped it off the bulkhead, but that would have run the risk of damaging the case.
As for bringing a portion of the aircraft to the surface, that is certainly possible. The bigger the portion, the more difficult the task, but in the case of the investigation I was part of, we brought the empennage and the flight compartment of the aircraft to the surface for inspection. Special tools on the ROV were used to detach these sections of the aircraft from the rest of the fuselage.