Passengers aboard the ill-fated tourist helicopter that crashed in New York City's East River Sunday may have drowned because they couldn't unfasten their safety harnesses. 

The chopper plunged into the waterway after pilot Richard Vance made a "Mayday" appeal for help, citing engine failure. All five passengers died, but Vance survived.

The doors to the Eurocopter AS350 were open so passengers could snap photos. But when the vessel went down, the open doors allowed the interior to quickly fill with water and the passengers were unable to get free of their harnesses, authorities said.

The victims were identified as Daniel Thompson, 34, and Tristian Hill, 29, both of New York, Trevor Cadigan, 26, and Brian McDaniel, 26, both of Dallas and Carla Vallejos Blanco, 29, of Argentina.

Vance suggested the strap of a passenger's bag somehow got wrapped around the fuel shut-off switch, accidentally stopping the aircraft's fuel supply to the engine, according to reports.

Rescuers had to cut the passengers' harnesses to free them from the wreckage. The pilot had been able to slip out of the restraining device. 

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