On April 12, 1985, a Hiller UH12J3 (registration N545HA) operated by Western Helicopter Services, was involved in an aviation accident near Klamath, CA. Investigators recorded the probable cause as: A self-locking nut was missing and a bolt had backed out of the upper firewall bellcrank assembly, resulting in the loss of cyclic control. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter returning from a reconnaissance flight prior to a sprating operation lost cyclic control at about 10 ft AGL after flaring, causing rotor strike. Investigation found a missing self-locking nut and backed-out bolt in the upper firewall bellcrank assembly.
Incident Description
A helicopter was returning to a private landing pad after completing a reconnaissance flight prior to a sprating operation. During the approach, the pilot flared and leveled the aircraft at an altitude of approximately 10 feet above ground level. At that point, the pilot could no longer control a drift and roll to the left. Within about one second, the rotor blades struck the ground.
Investigation Findings
An investigation into the accident revealed that a self-locking nut was missing from the upper firewall bellcrank assembly. Consequently, a bolt had backed out of the assembly. This condition resulted in the loss of cyclic control, which prevented the pilot from correcting the aircraft's attitude and led to the rotor strike.
Probable cause
A self-locking nut was missing and a bolt had backed out of the upper firewall bellcrank assembly, resulting in the loss of cyclic control.