begins. how do you pull a plane up from the bottom of the ocean? >> what you want to do first is to really map the entire accident scene. >> reporter: we spoke with peter gels former investigator with the ntsb who work read the recovery and rebuilding of twa flight 800 that crashed after takeoff in new york city. >> you document everything until you really get the information off the data recorder and the voice recorder. >> he says the site needs to be treated like a cream scene and mapping the debris field before removing objects could be key to finding out what happened. then comes the process of pulling up the giant pieces of debris from the bottom of the sea. >> you would have a number of -- of lifting cranes and you would have teams of divers and the divers of course even working at 100-foot depth you'll have to have decompression chambers. >> a potentially slow process because divers can only remain