Aviation experts have cast doubt on the pilot’s reported theory of what caused a fatal helicopter crash in Manhattan’s East River Sunday evening.

The pilot, 33-year-old Richard Vance, was the only survivor after the sightseeing helicopter suffered engine failure, and was forced to crash land in the East River, near the Upper East Side.

According to the New York Post, Vance told investigators he believes that a tether on one of the passenger’s harnesses inadvertently triggered the fuel shutoff switch during the flight. All five passengers were strapped tightly into harnesses because the doors on the flight were open to allow for the passengers to take photos and video. After the helicopter landed in the East River, it became quickly submerged, and the victims drowned before they could free themselves from the harnesses.

Earlier reports that indicated the pilot thought one of the passenger’s bags was involved in the malfunction appear to be incorrect.

Aviation lawyer Gary C. Robb told the New York Post that he doubts Vance’s theory about a loose harness tether causing the accident, calling it “highly improbable.”

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

National Transportation Safety Board is reportedly investigating the accident, which claimed the lives of Daniel Thompson, 34; Trevor Cadigan, 26; Tristan Hill, 30; Brian McDaniel and Carla Vallejos-Blanco, 29.

At a press conference, NTSB Vice Chair Bella Dinh-Zarr was asked if she thought Vance’s theory was credible.

“I have personally not seen this type of accident happen,” Dinh-Zarr said.

Seasoned helicopter pilot and aviation instructor Cliff Browne told the New York Post that there may have been a better outcome if Vance had landed the helicopter in Central Park, something he reportedly considered, the eventual water landing was handled expertly.

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

[Feature image: Associated Press]