The five passengers who were killed when a helicopter without doors splashed into the East River on Sunday night were cinched into heavy-duty harnesses and tied to the helicopter floor with only a knife to free themselves from frigid waters. Given little more than a brief safety video beforehand, they were left at the mercy of a stiff current as the helicopter dragged them 50 blocks south, upside down and underwater, before rescue divers could cut them free.

The crash — the deadliest involving a helicopter in New York City since 2009 — exposed what aviation experts called startling safety gaps in the fast-growing industry of doors-off photo flights, once reserved for professional photographers but increasingly marketed to tourists looking to dangle their feet outside and share stomach-churning pictures of the skyline on Instagram. In major cities, including Miami, Los Angeles and San Francisco, sightseers who are untrained, unaware of proper escape maneuvers and underdressed for wind-whipped conditions routinely climb into the doors-off helicopters, with regulatory agencies providing scant oversight.

Before circling the Statue of Liberty and heading toward Manhattan on Sunday night, passengers watched a roughly 10-minute video that showed them a knife in their harnesses they could use if they got trapped. But the briefing did not include any discussion about how to saw through the nylon ties should the helicopter need to ditch in the water surrounding Manhattan. And one passenger who watched the presentation before boarding a different flight said the staff never pointed out the knives once they were strapped in, leaving him oblivious to where his was.

The harnesses, tangles of thick straps and metal clasps that let tourists lean out over the skyline without worry, quickly became underwater death traps.