On May 13, 1990, an Enstrom F-28A (registration N9056) was involved in an aviation accident near Marathon, FL. Investigators recorded the probable cause as: The failure of the tail rotor gearbox due to a fracture in the casting around the input drive gear, accompanied by signs of logjamming within the interior of the casting. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A sightseeing helicopter lost tail rotor control shortly after takeoff, forcing the pilot to land in the ocean. Investigation revealed a failed gearbox casting with signs of internal logjamming.
What happened
The aircraft was operating as a sightseeing flight when it departed from its base. Shortly after liftoff, the helicopter reached an altitude of approximately 50 feet above the ground. At this point, the pilot experienced a complete loss of tail rotor drive and control authority. In response to the mechanical failure, the pilot attempted a powered forced landing into the adjacent ocean.
The investigation
Recovery efforts focused on the damaged helicopter components retrieved from the water. Examination of the tail rotor gearbox revealed that the failure originated at the casting surrounding the input drive gear. Physical evidence indicated signs of logjamming within the interior of this casting. Unfortunately, the drive gear itself was not recovered from the ocean, limiting the scope of mechanical analysis to the gearbox housing.
Findings
The primary mechanical issue was identified as a failure of the tail rotor gearbox. The specific point of failure was the casting around the input drive gear, which exhibited evidence of internal obstruction or logjamming. This mechanical disruption led directly to the loss of directional control during the initial phase of flight.
Probable cause
The failure of the tail rotor gearbox due to a fracture in the casting around the input drive gear, accompanied by signs of logjamming within the interior of the casting.