Accident Overview
On October 30, 2008, at approximately 0840 mountain daylight time, a Hiller UH-12E helicopter (registration N61436) experienced a flight control system malfunction while maneuvering about 5 miles west-southwest of Powder River, Wyoming. The pilot, unable to maintain control, executed a hard forced landing on the slope of a hillside. Upon touchdown, the helicopter rolled over and sustained substantial damage. The commercial certificated pilot received a minor injury, while the passenger was not injured. The helicopter was owned and operated by Wyoming Air Corporation of Casper, Wyoming. Visual meteorological conditions prevailed at the time of the aerial observation (predator control) flight, and no flight plan was filed. The flight was conducted under 14 Code of Federal Regulations Part 91 and originated from a refueling vehicle near Powder River at about 0830.
Pilot Report
The pilot reported to the National Transportation Safety Board investigator that the accident occurred while maneuvering at approximately 50 feet above ground level during a coyote-spotting operation. Suddenly, one blade associated with the control rotor assembly separated from the helicopter, initiating a violent vibration. The pilot stated that the vibration prevented him from reading the airspeed indicator and that he had only minimal control of the helicopter.
Examination Findings
During the subsequent examination of the helicopter, one of the two control rotor blade assemblies (Hiller part number 36209-3) was found separated from the rotor head. The rotor control blade assembly tube was observed cracked and broken off outboard of the two bolts attaching it to the cuff assembly. The helicopter had been operated approximately 21 hours since receiving its last annual inspection.