Pilot claims loose tether may be to blame

The pilot of the helicopter that plunged into the East River told cops he believes that a loose tether on one of his passengers’ harnesses cut off the fuel switch, law-enforcement sources said Monday.

The National Transportation Safety Board is investigating the scenario, sources said.

But one expert told The Post that the theory is “highly implausible” since the lever, which is on the floor next to the pilot’s seat in that type of chopper, needs to be pulled up and back to be activated — and “is normally fixed with a breakaway [safety] wire.

“I suspect a more plausible explanation is that the pilot simply activated the wrong lever, and this sometimes happens,” said aviation lawyer Gary C. Robb.

NTSB Vice Chair Bella Dinh-Zarr, asked at a press conference whether she had heard of a helicopter shutting down because someone triggered the wrong switch, responded, “We’ve seen many things that have happened in an airplane.

“I have personally not seen this type of accident happen,” she added.

The chopper was carrying five passengers and pilot Richard Vance when it crashed into the river at 7:08 p.m. Sunday before capsizing and sinking. Vance, 33, was the sole survivor.

“Zero Lima Hotel, mayday, mayday!” Vance had radioed to air-traffic controllers at La Guardia Airport, referring to the Eurocopter AS350’s tail number, N350LH, just moments before the crash.

“Lima Hotel, you OK?” a controller replied.

“Engine failure!” Vance repeated multiple times as the controller struggled to hear him.

Vance, who has been flying for nine years, told police “he didn’t want to set [the chopper] down in Central Park, so he headed to the river,” the source said.

That decision might have been fateful, according to longtime flight instructor and helicopter pilot Cliff Browne.

Based on the video he saw of the accident, Browne said the pilot was performing what is known as an “emergency autorotation maneuver” — using the energy from air rushing through the rotors to pull the front up and settle the craft down gently.

“The guy actually did it perfectly, but it turned over, and [the passengers] couldn’t get out, and they drowned,” Browne said.