Investigators were wrestling with a thicket of questions after the crash. Among them were what caused it, why the helicopter’s yellow inflatable pontoons did not keep it from flipping over and sinking and what more, if anything, the pilot could have done afterward to save his passengers.
The victims were Trevor Cadigan and Brian McDaniel, both 26, high school friends from Dallas; Carla Vallejos Blanco, 29, of Corrientes, Argentina; and Daniel Thompson, 34, and Tristan Hill, 29, who a law enforcement official said were both employees of the helicopter company that operated the flight.
The pilot, Richard Vance, 33, a former helicopter instructor from Connecticut, said on a mayday call that there was “engine failure.” He later told investigators that the fuel shut-off switch may have inadvertently been hit by passengers or somehow become wrapped up in onboard equipment or a strap, choking off supply to the engine. Aviation experts said it was not clear how that could have happened, given that the switch was on the floor in the front area of the cabin and that loose objects are barred from doors-off flights.
Aviation experts said the helicopter appeared in cellphone video to have made a gradual descent that passengers could have survived, had the helicopter not tipped over and submerged. That raised questions about whether the pontoons — flotation devices activated by the pilot or by contact with water that run along the landing skids — were properly inflated. Investigators for the National Transportation Safety Board said at a news conference on Monday that all the pontoons deployed, but they were examining how quickly and whether they had been properly maintained.
Senator Chuck Schumer of New York, the Democratic leader, called on the Federal Aviation Administration to suspend the license of Liberty Helicopters, the large sightseeing and charter company based in New Jersey that owns and operates the Airbus AS350 B2 that crashed.
The company has a checkered safety record. It was also involved in a collision over the Hudson River in 2009, in which a helicopter hit a small private plane, killing six people on the helicopter and three on the plane. Two years earlier a Liberty tour helicopter crashed into the Hudson River; all the occupants survived.
Bruce Hunt, an aviation safety consultant in Colorado, said tour companies have terrible safety records. “They kill people every year,” he said.
Previous crashes have often prompted calls to restrict helicopter traffic in the crowded skies over Manhattan. But aviation experts on Monday homed in on the lightly regulated, little-known industry of doors-off photo flights.
FlyNYON, the company that booked the flight, says on its website that it makes the thrill of taking pictures from an open-sided helicopter “accessible to everyone.”
Customers are not required to have any training in photography or experience with helicopters, but they must be at least 12 years old.
Mr. Hunt said Liberty would likely have needed a supplemental-type certificate from the aviation administration to use the harnesses. But it was unclear what rules, if any, dictated the kind of harnesses required on an open-sided helicopter.
Citing the pending investigation, a spokesman for the aviation administration declined to say what special permissions Liberty had.
The N.T.S.B. investigators said it was legal for the helicopter that crashed to have its doors open, but answered few questions about whether it had prior mechanical problems or whether it met any other regulatory requirements for doors-off flights. Investigators said they would look at whether the harnesses worked.
The pilot spoke with local investigators after the crash and the N.T.S.B. said it would also seek an interview. FlyNYON Air and Liberty Helicopters said in separate statements that they were cooperating with the federal investigations.
Passengers started gathering about an hour early for the 6:45 p.m. flight from New Jersey on Sunday. Eric Adams, an aviation journalist and photographer who was assigned to a different flight at the same time, said some of the passengers on the helicopter that crashed were dressed in light jackets, having apparently never been told by the tour company how cold it could get with the doors open and rotors spinning above.
Mr. Adams said some of the preparations seemed careful and deliberate. But he said there were no pilots or safety experts at the video presentation, which he said omitted certain important warnings, like how to avoid the rotors while escaping a downed helicopter.
Riders were strapped in from the rear, with a carabiner attaching the back of their harness to a tether that connected to the helicopter. They were also buckled in with seatbelts. Mr. Adams said even though he had flown in similar helicopters before, he did not know where his knife was or how to unlock the carabiner.
“The training that we had before takeoff wasn’t good enough to prepare anybody for what could happen,” he said. “They just need a better harness system. They’re not adequate.”
After Mr. Vance’s helicopter encountered trouble shortly after 7 p.m., Mr. Vance “pointed away from the city and toward the river,” a law enforcement official said. “He didn’t want to go down in Manhattan, so he went toward the river, because it seemed like the best option for a landing.”
A tugboat, the Foxy 3, was returning to its base on Staten Island when the men aboard apparently heard the mayday call, the official said. They helped rescue the pilot and tied off the helicopter to keep it from sinking 50 feet to the bottom of the river.
Rescue divers arrived on scene minutes after the first 911 call. But unable to dive in while the tug propellers were on, they had to tell the captain to cut the propellers. A three-knot current dragged them south as they tried to cut the passengers out. The police and firefighter divers appeared to free one passenger soon after submerging, but it may have taken until the helicopter drifted from 86th Street to a pier at 34th Street for the divers to free the rest of the passengers, the official said.
After Mr. Adams’s helicopter returned to the base in New Jersey, he went to retrieve his belongings from a big locker where passengers on all the evening flights had stored items to avoid them falling out of the helicopter. He and his companions removed their belongings, but there were still things sitting at the bottom of the locker when he left that no one retrieved: a few wallets, car keys and a purse.