HILLER UH-12E near Powder River, WY — 2008-10-30

Probable cause

A flight control system malfunction while the helicopter was maneuvering at low altitude due to the failure/separation of the rotor blade control tube.

NTSB narrative

While maneuvering about 50 feet above ground level during an aerial observation flight, one blade associated with the control rotor assembly separated from the helicopter, and a violent vibration started. Unable to maintain control, the pilot made a forced landing on the underlying sloping terrain, and the helicopter rolled over. During the subsequent inspection of the rotor system, one of the two control rotor blade assemblies was found separated from the rotor head. A rotor blade control tube had cracked and broken off outboard of the two attachment bolts. The component had been operated 21 hours since receiving its last inspection. The reason for the cracking and separation of the control tube could not be determined.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Pilot could have aborted the flight upon noticing control issues.

NTSB coding

• Flight control sys malf/fail · Maneuvering-low-alt flying

Evidence available

• 1 docket document

Docket documents1

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form

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