Fatalities include a Dallas firefighter and an Argentine tourist

A fatal helicopter crash Sunday in New York that killed five passengers who were trapped underwater has exposed safety concerns in the helicopter-tour industry.

The helicopter’s pilot said one of the passengers’ bags might have inadvertently hit the emergency fuel-shutoff button, according to a person familiar with the investigation. The pilot had radioed in a mayday call just before the crash, saying: “East River, engine failure.”

New York City officials said divers who sought to rescue the passengers trapped in the submerged, inverted Eurocopter AS350 helicopter had trouble releasing the passengers—four men and one woman—from their harnesses. The passengers had signed up for a photo tour of New York City that requires more complicated safety harnesses because the tours are often done with the doors open.

Read: Expert doubts helicopter pilot’s ‘tether’ crash theory

National Transportation Safety Board investigator Todd Gunther said Monday that the agency will be looking into the harness system as part of its continuing investigation.

Despite high-profile government and industry safety initiatives, both the total number and frequency of serious U.S. helicopter crashes has remained high in recent years.