What aircraft was involved and where did it happen?

The accident on 1987-04-11 involved a Hughes 369E, registration N5200W, at Palm Desert, CA.

Helicopter Crashes in Residential Area After Tail Rotor Gearbox Failure (N5200W)

On April 11, 1987, a Hughes 369E (registration N5200W) was involved in an aviation accident near Palm Desert, CA. Investigators recorded the probable cause as: Failure of three tail rotor gearbox mounting studs from cyclic fatigue due to bending resulting from loss of clamp-up torque; subsequent overload failure of the gearbox ear; and installation of three washers per stud instead of the permitted one during… 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 1781061362Data API Editorial standards

A helicopter descended uncontrolled and crashed in a residential area after the pilot felt a bang and severe tail vibration. Examination revealed failure of three tail rotor gearbox mounting studs and installation of extra washers during compliance with an airworthiness directive.

Accident Description

A helicopter descended uncontrollably and crashed in a residential area. The accident occurred while the helicopter was orbiting the residence of a passenger.

Pilot Account

After the accident, the pilot reported that he had agreed to orbit the passenger's residence. During the left orbit, at approximately the 135-degree point, he felt a bang and severe vibration in the tail. He then lost directional control, and the helicopter began spinning to the right.

Investigation Findings

Examination of the tail rotor gearbox (T/R GB) assembly revealed that three of the four T/R GB mounting studs had failed from cyclic fatigue due to bending, which resulted from a loss of clamp-up torque. Subsequently, the lower right ear of the T/R GB, at the location of the fourth stud, failed from overload, causing the T/R GB to separate.

Further investigation disclosed that three washers had been installed on each of the mounting studs, but only one washer was permitted per the manufacturer's specifications. These washers were installed during compliance with Airworthiness Directive (AD) 86-20-07, approximately 78 flight hours before the accident.

Probable cause

Failure of three tail rotor gearbox mounting studs from cyclic fatigue due to bending resulting from loss of clamp-up torque; subsequent overload failure of the gearbox ear; and installation of three washers per stud instead of the permitted one during compliance with AD 86-20-07.

Maintenance error

1987-04-11: Hughes 369E (N5200W) — Palm Desert, CA