“Mayday, mayday, mayday,” the pilot is heard saying during the crash Sunday night. “East River — engine failure.”

The Associated Press

NEW YORK — A pilot who survived when his helicopter went down in New York City’s East River, killing five passengers, said in an emergency radio transmission that the aircraft’s engine had failed.

“Mayday, mayday, mayday,” the pilot is heard saying during the crash Sunday night. “East River — engine failure.”

The pilot freed himself and was rescued by a tugboat, but emergency divers had to remove the passengers on the charter helicopter being used for a photo shoot from tight safety harnesses while they were upside down, Fire Commissioner Daniel Nigro said.

“It took a while for the divers to get these people out. They worked very quickly, as fast as they could,” Nigro said. “It was a great tragedy that we had here.”

The National Transportation Safety Board dispatched investigators on Monday.

Video taken by a bystander and posted on Twitter shows the red helicopter land hard in the water and then capsize, its rotors slapping at the water.

Witnesses on a nearby waterfront esplanade said the helicopter was flying noisily, then suddenly dropped and quickly submerged. But the pilot appeared on the surface, holding onto a flotation device as a tugboat and then police boats approached.

“It was sinking really fast,” Mary Lee, 66, told the New York Post. “By the time we got out here, we couldn’t see it. It was under water.”

A Federal Aviation Administration spokeswoman said the Eurocopter AS350 went down just after 7 p.m. The aircraft was owned by Liberty Helicopters, a company that offers both private charters and sightseeing tours popular with tourists.

The company referred inquiries to authorities, saying it was focused on the victims’ families and the investigation.

The skies over New York constantly buzz with helicopters carrying tourists, businesspeople, traffic reporters, medical teams and others.

In 2009, a sightseeing helicopter of the same model and operated by the same company as the one in Sunday’s wreck collided with a small, private plane over the Hudson River, killing nine people, including a group of Italian tourists.

A crash in October 2011 in the East River killed a British woman visiting the city for her 40th birthday. Two other passengers died weeks later as a result of their injuries.

A helicopter on a sightseeing tour of Manhattan crashed into the Hudson River in July 2007, shaking up the eight people aboard but injuring no one. In June 2005, two helicopters crashed into the East River in the same week. One injured eight people including some banking executives. The other hit the water shortly after takeoff on a sightseeing flight, injuring six tourists and the pilot.

Nigro and Police Commissioner James O’Neill said the rescue operation Sunday took place in a 4 mph current in water about 50 feet (15 meters) deep, under challenging conditions.

The cause of the crash has not been determined.