TAMPA, Fla. (WFLA) — Authorities are investigating why the door from a twin-engine helicopter fell off mid-flight Wednesday with five people aboard.

The Federal Aviation Administration (FAA) said a Messerschmitt-Bölkow-Blohm Bo 105 helicopter was flying southwest of Page Field Airport in Fort Myers around 10 a.m when a rear passenger door fell off.

The FAA said the door plummeted onto the roof of a local business. The helicopter returned safely to the airport.

It is unclear as of this report what caused the door to fall off.

This is a developing story. Stay up to date on the latest from News Channel 8 on-air and on the go with the free WFLA News Channel 8 mobile app.