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Tail Rotor Separation Leads to Hard Landing in Helicopter Accident (N9846F)

Lorida, FL, US

On June 28, 1996, a Bell UH-1B (registration N9846F) was involved in an aviation accident near Lorida, FL. Investigators recorded the probable cause as: The mounting bolts were not torqued properly, leading to bending fatigue failure of the gearbox mounting studs, which caused the tail rotor gearbox, hub, and blades to separate in flight. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-07-04Data APIEditorial standards

A helicopter experienced tail rotor separation in flight, causing a spin. The pilot managed to level the aircraft but touched down sideways, resulting in main rotor ground contact. Investigation revealed improperly torqued mounting bolts led to fatigue failure of gearbox mounting studs.

Accident Overview

During flight, the tail rotor gearbox, hub, and blades separated from the helicopter. The loss of the tail rotor caused the helicopter to spin to the right. The pilot responded by reducing engine power and leveling the helicopter. However, the helicopter touched down moving sideways, and the main rotor blades contacted the ground.

Investigation Findings

Postcrash examination of the gearbox revealed that the mounting studs had failed due to bending fatigue. The fatigue failure was a result of the mounting bolts not being torqued properly. Logbook records indicated that the gearbox had been replaced 95 flight hours before the accident.

Conclusion

The accident was caused by the separation of the tail rotor assembly due to fatigue failure of the gearbox mounting studs, which resulted from improper torque of the mounting bolts. No other contributing factors were identified.

Probable cause

The mounting bolts were not torqued properly, leading to bending fatigue failure of the gearbox mounting studs, which caused the tail rotor gearbox, hub, and blades to separate in flight.
Maintenance error

Frequently asked questions

What happened in the 28 Jun 1996 Bell UH-1B accident near Lorida, FL?

A helicopter experienced tail rotor separation in flight, causing a spin. The pilot managed to level the aircraft but touched down sideways, resulting in main rotor ground contact. Investigation revealed improperly torqued mounting bolts led to fatigue failure of gearbox mounting studs.

What aircraft was involved and where did it happen?

The accident on 28 Jun 1996 involved a Bell UH-1B, registration N9846F, at Lorida, FL.

What was the probable cause of the accident?

The mounting bolts were not torqued properly, leading to bending fatigue failure of the gearbox mounting studs, which caused the tail rotor gearbox, hub, and blades to separate in flight.

More accident analyses

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001208X06071. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.