Background
The aircraft (N21ST) was en route on a flight from Key West to Naples, Florida. During the flight, the pilot of another aircraft observed a 'fireball' in the vicinity where N21ST subsequently crashed. When N21ST did not arrive at its destination, a search was initiated.
Discovery of Wreckage
The wreckage was found the next day at 1704 EST, in the Everglades National Park, near Flamingo, Florida. During impact, the main wreckage was buried in 30 feet of mud. The left outboard wing section, extending from just outboard of the engine nacelle to the wing tip, was found approximately 1 mile from the main wreckage.
Examination Findings
An examination of the wing revealed that it had failed at the location where the nacelle fuel tank and the auxiliary fuel tank boost pumps were mounted. No exhaust system failure or leakage from the fuel tanks was found in the area of the fire. The greatest fire damage was identified at a point where the left nacelle fuel tank boost pump was mounted and extended aft from there to where the rear wing spar had burned through. The electrical fuel boost pumps were not recovered after the accident. The ignition source for the fire was not determined.
Occupants
All three occupants of the aircraft were killed.
Probable Cause
The official probable cause of the accident was: An undetermined airframe/component/system failure/malfunction, which resulted in a fuel fed fire in the left wing.