There was a scuffle and the pilot tried to manoeuvre the plane. The man fell on the throttle and made it so that he [the pilot] couldn't fly the plane

FBI agent Judy Orihuela

A fight broke out in the cockpit and the six-seater Piper Cherokee plane crashed into the sea between Key West and Cuba.

The pilot, 36-year-old Thomas Hayashi, managed to escape with cuts and bruises, but the couple are believed to have drowned when the plane sank.

FBI agent Judy Orihuela told Reuters news agency: "There was a scuffle and the pilot tried to manoeuvre the plane. The man fell on the throttle and made it so that he [the pilot] couldn't fly the plane."

The Coast Guard sent a crew to the scene after receiving a distress call.

Rescuers found Mr Hayashi in the water but there was no sign of the plane or the couple.

Ms Orihuela said the FBI "had no reason to disbelieve the pilot's story. But we still need to look at it."

Media reports say Mr Hayashi told police the couple had inflated their lifejackets while still inside the aircraft, which investigators believe may have hampered their escape.

Flights of fancy

The couple, who were in their sixties, booked the one-hour trip with Mr Hayashi's company, called Fly Key West, which offers customers the opportunity to have sex in an airplane.

Fly Key West's website advertises various excursions for up to $349, including offering a souvenir video of the trip.

The plane had reportedly been converted to a two-seater aircraft containing a 'lounge' area behind the cockpit.

The hijacking was the second recent bizarre incident involving a small plane in the Florida Keys.

Last month, an American pilot on a solo flying lesson crash landed his Cessna plane on a beach near the Cuban capital, Havana.