Overview
On August 1, 2014, at about 1415 central daylight time, a Mosquito XE amateur-built helicopter, Canadian-registered CF-HEZ, was substantially damaged during maneuvering near Wittman Regional Airport (KOSH) in Oshkosh, Wisconsin. The private pilot, who was the sole occupant, was not injured. Visual meteorological conditions prevailed for the flight, which was conducted under 14 Code of Federal Regulations Part 91 without a flight plan. The local flight had departed approximately five minutes earlier, at 1410.
The Accident Sequence
Just after takeoff, one tail rotor blade separated from the tail rotor and gearbox assembly. Following the separation, the helicopter began to rotate and subsequently impacted the ground in a level attitude. The impact spread both skids out horizontally. Both skids and the tail boom sustained substantial damage.
Post-Accident Examination
According to an inspector from the Federal Aviation Administration (FAA) who examined the helicopter, the tail rotor blade had separated cleanly from the assembly. Neither the collar nor the pins used to secure the blade were located. The inspector reported that the tail rotor assembly was a unique design being tested and was not used in any other application.
Pilot Report
The pilot reported that he had been testing this tail rotor design for four years. He stated that a tension/torsion strap and two steel pins were used to retain the blade. According to the pilot, the strap was not completely restricted from movement, and over time, movement and wear resulted in the failure of the retaining assembly. The pilot further reported that the tail rotor assembly had accumulated 82 hours of operation, and it had been 6 hours since its last inspection.