What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
On August 1st, 2014 at approximately 1900Z, cfhez, a canadian registered amateur built helicopter was involved in an accident at the ultralight field at the Oshkosh airport (kosh) during airventure 2014. The aircraft?s pilot, and sole occupant, privacy data omitted, was not injured. The aircraft sustained substantial damage. The weather was VFR at the time, with light winds. It should be noted that privacy data omitted is this experimental aircraft?s designer, and builder.
The pilot was executing a visual approach, and while at a height of approximately 30? He heard a loud noise, and began an uncommanded yaw to the right. He correctly diagnosed a tail rotor failure, and entered an autorotation to the grass surface below. He landed in a nearly level attitude. The aircraft was resting on its belly with damage to the aft edge of the fiberglass tail boom, and spread skids. The tail rotor gearbox was found about 100 yards from the aircraft, and was missing a blade. Witnesses saw the aircraft lose the tail rotor blade on final.
The tail rotor on the aircraft was an experimental all carbon fiber unit that used tension/torsion straps running up through the center of the blades rather than the standard bearing/pin configuration that is used on the production kit of the Mosquito xe. It was an effort to produce an all carbon solution with no metal bearings, only iglide radial bearings and a tension/torsion strap for centrifugal loads. It had been on the helicopter for several years. After examining the tail rotor blade it appears that the tension/torsion strap in the blade had failed at the tip of the blade. There were two pins there that fastened the strap to the blade skin and countered the centrifugal force. It appears that movement in the area allowed the pins to work at the strap over time and wear through it causing it to fail and release the blade. The unbalanced remaining blade tore the gearbox off and resulted in the forced landing.
As the FAA filed it
ON AUGUST 1ST, 2014 AT APPROXIMATELY 1900Z, CFHEZ, A CANADIAN REGISTERED AMATEUR BUILT HELICOPTER WAS INVOLVED IN AN ACCIDENT AT THE ULTRALIGHT FIELD AT THE OSHKOSH AIRPORT (KOSH) DURING AIRVENTURE 2014. THE AIRCRAFT?S PILOT, AND SOLE OCCUPANT, ^PRIVACY DATA OMITTED^, WAS NOT INJURED. THE AIRCRAFT SUSTAINED SUBSTANTIAL DAMAGE. THE WEATHER WAS VFR AT THE TIME, WITH LIGHT WINDS. IT SHOULD BE NOTED THAT ^PRIVACY DATA OMITTED^ IS THIS EXPERIMENTAL AIRCRAFT?S DESIGNER, AND BUILDER.
THE PILOT WAS EXECUTING A VISUAL APPROACH, AND WHILE AT A HEIGHT OF APPROXIMATELY 30? HE HEARD A LOUD NOISE, AND BEGAN AN UNCOMMANDED YAW TO THE RIGHT. HE CORRECTLY DIAGNOSED A TAIL ROTOR FAILURE, AND ENTERED AN AUTOROTATION TO THE GRASS SURFACE BELOW. HE LANDED IN A NEARLY LEVEL ATTITUDE. THE AIRCRAFT WAS RESTING ON ITS BELLY WITH DAMAGE TO THE AFT EDGE OF THE FIBERGLASS TAIL BOOM, AND SPREAD SKIDS. THE TAIL ROTOR GEARBOX WAS FOUND ABOUT 100 YARDS FROM THE AIRCRAFT, AND WAS MISSING A BLADE. WITNESSES SAW THE AIRCRAFT LOSE THE TAIL ROTOR BLADE ON FINAL.
THE TAIL ROTOR ON THE AIRCRAFT WAS AN EXPERIMENTAL ALL CARBON FIBER UNIT THAT USED TENSION/TORSION STRAPS RUNNING UP THROUGH THE CENTER OF THE BLADES RATHER THAN THE STANDARD BEARING/PIN CONFIGURATION THAT IS USED ON THE PRODUCTION KIT OF THE MOSQUITO XE. IT WAS AN EFFORT TO PRODUCE AN ALL CARBON SOLUTION WITH NO METAL BEARINGS, ONLY IGLIDE RADIAL BEARINGS AND A TENSION/TORSION STRAP FOR CENTRIFUGAL LOADS. IT HAD BEEN ON THE HELICOPTER FOR SEVERAL YEARS. AFTER EXAMINING THE TAIL ROTOR BLADE IT APPEARS THAT THE TENSION/TORSION STRAP IN THE BLADE HAD FAILED AT THE TIP OF THE BLADE. THERE WERE TWO PINS THERE THAT FASTENED THE STRAP TO THE BLADE SKIN AND COUNTERED THE CENTRIFUGAL FORCE. IT APPEARS THAT MOVEMENT IN THE AREA ALLOWED THE PINS TO WORK AT THE STRAP OVER TIME AND WEAR THROUGH IT CAUSING IT TO FAIL AND RELEASE THE BLADE. THE UNBALANCED REMAINING BLADE TORE THE GEARBOX OFF AND RESULTED IN THE FORCED LANDING.