"Our best estimate is that the floats deployed as a result of collision with terrain. It appears that the helicopter struck the ground, (then) the floats deployed," he said.

Rayner, who is the NTSB's lead investigator on the crash, said a single eyewitness account seems to indicate the aircraft was coming in for a run-on landing, in which the aircraft lands with forward speed and slides on its skids, but that it tipped forward at the last moment, and crashed on its nose. During the process, there may also have been damage from the main rotor striking part of the helicopter body.

"There was some evidence of blade impact, but the most significant deformation was crush deformation," Rayner said.