Primary finding
Probable cause
The fatigue failure during hover of the drive adapter between the engine and lower pulley drive shaft.
Investigator assessment
Analysis narrative
After a hover taxi and while approximately 5 feet above ground level, the pilot stopped the helicopter's forward movement, and was turning into the wind when he felt a "hard thump." The helicopter descended, impacted the ground, and yawed 20-30 degrees to the left before coming to rest in an upright position. The helicopter sustained minor damage. An examination of the helicopter by maintenance personnel revealed that the forward drive adapter of the engine to lower pulley drive shaft had fractured and separated from the aft coupling. This fracture separated the engine from the power train, resulting in loss of power to the main rotors. An examination of the drive adapter revealed that it had failed due to fatigue.
Source record
Factual narrative
On September 30, 2007, about 1705 central daylight time, a single-engine Schweizer 269D helicopter, N8374F, sustained minor damage during a forced landing at the William P Hobby Airport (HOU), near Houston, Texas. The commercial pilot and observer were not injured. The helicopter was registered to and operated by the Houston Police Department. Visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 91 flight. The local flight was originating at the time of the accident. The pilot reported that after a hover taxied and while approximately five feet above ground level, he stopped the helicopter's forward movement and was turning into the wind when he observed a "hard thump." The helicopter descended, impacted the ground, and yawed 20-30 degrees to the left before coming to rest in an upright position. An examination of the helicopter by maintenance personnel revealed that the forward drive adapter of the engine to lower pulley drive shaft, KaFlex assembly part number SKCP2738-7 fractured and separated from the aft coupling. This fracture separated the engine from the power train resulting in loss of power to the main rotors. An examination of the drive adapter was performed at Schweizer Aircraft Corporation with oversight provided by the Federal Aviation Administration. The examination revealed that the drive adapter had failed due to fatigue.