What happened
A commercial sightseeing flight was operating in the vicinity of Key West with two passengers, an elderly Hispanic couple. Upon reaching cruising altitude, a male passenger entered the cockpit while armed with a knife. The passenger turned off the aircraft's radios and transponder and demanded that the pilot fly to Cuba.
In an effort to prevent the hijacking, the pilot executed a maneuver to produce negative g-forces to incapacitate the hijacker and attempted to return to Key West. During the struggle, the hijacker fell against the retarded throttle, bending it. An attempt to straighten the throttle shaft resulted in the shaft snapping off, leaving the aircraft with only idle power available.
The pilot performed a ditching using idle power. The impact with the water was violent, causing forward motion to stop abruptly and resulting in the two passengers appearing to lose consciousness. The pilot exited through the right cockpit door, inflated his life vest, and swam toward the passenger door to rescue the occupants. However, the aircraft began sinking before the door could be opened. The two passengers went down with the aircraft, and neither the aircraft nor the passengers have been recovered. The pilot was subsequently rescued by a U.S. Navy helicopter.
Findings
The investigation determined that the mechanical failure of the throttle system was caused by the physical struggle in the cockpit, specifically when the throttle shaft snapped after being bent during the altercation.