Sen. Chuck Schumer Sunday demanded a probe into the FAA policies that contributed to the deaths of five helicopter passengers last week — questioning how the treacherous harnesses and “doors off” flights were ever allowed in the first place.

While the FAA Friday banned “open door” flights in the wake of the East River crash — where the passengers who were unable to escape their complex harnesses drowned — Schumer is calling for an Inspector General and National Transportation Safety Board investigation.

His appeal, which comes one week after the horrifying deaths of Trevor Cadigan, Tristan Hill, Daniel Thompson, Daniel Thompson, Carla Vallejos-Blanco, is joined by Sen. Kirsten Gillibrand.

In a letter obtained by The Post, both Schumer and Gillibrand implore the Inspector General to take further action.

“A deep dive into the FAA policies and practices for reviewing the crashworthiness of helicopters is clearly needed in this case,” they write to Inspector General Scovel III and Vice Chairman Dinh-Zarr. “Your two agencies should work together to accomplish that. In addition, your agencies should thoroughly review that exact review, testing, and approval process that was conducted before authorizing this specific safety and restraint system.”

In a separate missive, Schumer admitted that while “‘doors-off’ helicopter tours may have offered an Instagram-worthy experience,” to clientele, their current safety standards “put passengers in insta-danger.”

“While I applaud the FAA for quickly moving to halt these types of helicopter flights, I am demanding to know how they were allowed to take off in the first place. Doors- off flights and this questionable restraint system should have been grounded from day one,” Schumer added. “The Inspector General and the NTSB should immediately launch an investigation to examine how exactly these flights were ever given the green light and ensure that helicopter operators across the country are adhering to modern safety regulations.

The March 11 flight, operated by Liberty Helicopters, was the third crash the company had seen since 2009, according to Schumer’s office. Nine people died when one of their choppers collided with a small private plane flying over the Hudson River in 2009.