Federal investigators said three floats on the right side of the helicopter which crashed in the East River March 1, killing five sightseers, did not properly inflate.

The under-inflated floats may have caused the ill-fated Liberty AS350 helicopter to flip over on its side as pilot Richard Vance executed an emergency water landing, the National Transportation Safety Board said.

Examination of the emergency float system revealed that the three floats installed on the left landing gear skid appeared to be more inflated than the floats on the right landing gear skid, the NTSB found.

Pilot Richard Vance told investigators that he initially thought his Liberty helicopter experience an engine malfunction causing it to shut down, according to the report.

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He tried desperately to re-start the engine and noticed the emergency shutoff lever was off and a portion of the front seat passengers tether was caught on the lever.

He briefly thought about landing in Central Park but concluded there were too many people, the NTSB said.

Investigators did not find signs of oil or fuel leaks or fire.