The National Transportation Safety Board on Tuesday said the deadly East River Helicopter crash 20 months ago that killed five people was survivable — but it said the companies that chartered and owned the helicopter were able to bypass crucial safety requirements.

"They intentionally exploited a regulatory loophole to the detriment of their customers' safety," Robert L. Sumwalt, the chairman of the National Transportation Safety Board (NTSB), said at a board meeting.

Liberty Helicopters owned the chopper and FlyNYON chartered it, billing the no-door sightseeing flights as "aerial photography." That allowed them to avoid tougher federal oversight imposed on traditional sightseeing air tours.

Investigators found the companies knew of the exception and told employees to avoid phrases like "air tour" and "sightseeing" to keep flying under less oversight.

"Exploited an opportunity to just avoid federal regulation. That is exactly what they were doing," NTSB member Jennifer Homendy said.

Six months before the crash, a Federal Aviation Administration (FAA) inspector flagged the operation of a FlyNYON chopper under the looser safety standard as "unorthodox." But the agency allowed the flights to continue.

"Lacking appropriate guidance documents, FAA inspectors appeared to believe that they could not push back on Part 91 general aviation status of the flights or inspect them. Glaring safety deficiencies were present and cloaked in the exception," Sumwalt said.

All five passengers aboard the door-less flight died when a tether attached to the harness of one passenger caught the fuel shutoff lever. The chopper went down in the East River.

The NTSB said that was the primary cause of the crash, and that the five were doomed because they could not detach unapproved full body harnesses that were used with the tethers so they could hang their feet over the open doors and take photos. The pilot wearing a different, FAA-approved restraint, was able to escape.

"The contraption that FlyNYON rigged up turned a perfectly good helicopter into a death trap. That is a fact," Sumwalt said.

"Safety has always been FlyNYON's first priority and we have made changes to our operations to help ensure an accident like this never happens again," a FlyNYON spokesperson said in a statement.

Liberty Helicopters said it could not comment on the investigation.