The United States Army Corp of Engineers, working with the National Transportation Safety Board and NYPD divers, lift the red Eurocopter Helicopter involved in the multi-fatal crash from the docks at East 23rd Street at the East River in Manhattan on Monday, March 12, 2018. Credit: Theodore Parisienne/New York Daily News/TNS

Federal crash investigators said they will examine the role of hard-to-remove harnesses that may have trapped five passengers in a helicopter that ditched in the East River in New York on Sunday.

The harnesses, which are different than traditional aircraft seat belts, are designed to allow people to safely take photographs from a helicopter with the doors open. They attach from the rear and could be difficult to remove in an emergency, according to a passenger on another flight who said he photographed the helicopter before the crash.

“We have heard information that’s come forward from a number individuals regarding the harness system in this particular helicopter and then also in sister helicopters,” the National Transportation Safety Board’s investigator-in-charge Todd Gunther said at a briefing Monday. “That’s something we’ll be looking into.”

[Journalist, firefighter among those killed when helicopter crashed into NY river]

Among the investigators on the NTSB’s team are so-called survival factors experts who have studied various aircraft restraint systems.

Divers in fast-moving, frigid waters had to cut the people loose 50 feet below the surface in order to remove them, New York Fire Department Commissioner Daniel Nigro said.

“It took a while for the divers to get these people out,” Nigro said at an earlier briefing.

Sen. Chuck Schumer, D-N.Y., called on the government to temporarily shut down the tour company, Liberty Helicopters. It has had two previous accidents, including a 2009 mid-air collision with a small private plane over the Hudson River that killed nine people.

The Federal Aviation Administration, which regulates flight-tour companies like Liberty, is conducting its own investigation to determine whether any rules were violated, the agency said in a statement. Liberty didn’t respond to a request for comment but posted a statement on its website saying it was “fully cooperating with the FAA and NTSB investigations.”

The company said that the agencies had asked them to “respect” the investigation by not commenting further.

The Airbus SE AS350 helicopter went down shortly after 7 p.m. near East 86th Street in Manhattan as the pilot declared an emergency. The pilot escaped as the craft sank and was rescued.

“Mayday, Mayday, Mayday,” the pilot told air traffic controllers as the helicopter was going down, according to a recording of the radio call. “East River. Engine failure.”

A video posted online appeared to show the red helicopter descending into the river, its spinning blades chopping the water as it tipped over. Helicopter rotors are designed to continue spinning if the craft loses power to slow its descent for a safe landing.

A man on Twitter who identified himself as a photographer named Eric Adams said that he took a helicopter flight at the same time as the one that crashed and posted photos of the ill-fated craft flying over the Statue of Liberty.

“It was a doors-off flight, with harnesses,” Adams said in a post about the flight that crashed. “They would have been difficult to remove in an emergency, since you’re attached from the rear.”

Another issue investigators are examining is the role of emergency floats on the helicopter, which were designed to prevent it from sinking in a water landing, said Bella Dinh-Zarr, the NTSB’s board member on scene.

The orange floats activated and could be seen on the helicopter as it was moored on the East River on Monday, but they didn’t prevent the aircraft from sinking.

The pilot has told law enforcement officials that he suspects a bag owned by one of the passengers may have switched an emergency shutoff valve for fuel to the engines, CNN and ABC News reported.

The NTSB, which sent a team of 15 to investigate the accident, hasn’t confirmed the report. Investigators hadn’t spoken to the pilot as of the Monday afternoon briefing, Dinh-Zarr said.

The helicopter was taken to an unspecified secure facility so it can be examined, the NTSB said Monday in a tweet.

“Since this was a photo flight, we will be working with the NYPD to recover any cameras or personal electronic devices from the aircraft that might paint an accurate digital portrait of the last moments of this flight,” Dinh-Zarr said.

Video of the helicopter’s takeoff was posted on Instagram by one of the victims.

In recent years, the NTSB has made growing use of photos and videos shot by people on flights, recovering the data even after devices were damaged.