History of Flight
On May 2, 2012, about 1140 mountain standard time, a Hughes 269C helicopter, registration N350TL, sustained substantial damage after colliding with a residential home near Phoenix, Arizona. The helicopter was owned and operated by Canyon State Aero of Mesa, Arizona. The certified commercial pilot sustained serious injuries, and the passenger sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed. The reported photo flight was being operated in accordance with 14 Code of Federal Regulations Part 91. The local flight departed Deer Valley Airport (DVT), Phoenix, Arizona, about 1115.
The pilot reported that after picking up his passenger/photographer, he departed DVT for a construction site. He proceeded southwest at about 500 feet above ground level and 70 to 75 knots. About 2 minutes before reaching the site, he detected a vibration in the back of his seat and in the anti-torque pedals, followed immediately by a right yaw not correctable with pedal input. He heard a "metallic clunking" sound and observed the tail rotor slowing. He elected to autorotate to a cul-de-sac, lowering collective and rolling off throttle. The helicopter initially impacted the roof of a house and a brick wall, coming to rest in the backyard of the adjacent house in a slightly nose-down, upright attitude. The pilot reported that main and tail rotor blades were intact and considered the event a mechanical failure.
Three witnesses provided statements. Witness #1 heard the helicopter sounding abnormal, sputtering, and observed it rocking and teetering before descending. Witness #2 heard sputtering, noted rpm fluctuations, saw the helicopter make a U-turn while losing altitude, and later turned off switches at the site. Witness #3 also heard abnormal engine sounds and observed the helicopter descending.
Personnel Information
The pilot, age 40, held a commercial pilot certificate with rotorcraft-helicopter, instrument helicopter, and helicopter instructor ratings. His most recent flight review was on March 29, 2012. He held a second-class FAA medical certificate dated December 31, 2011. He reported 1,460 total flight hours, all in helicopters, with 1,030 hours in make and model.
Aircraft Information
The accident helicopter was a Hughes Model 269C, serial number 0694C, manufactured in 1978. Its airworthiness certificate was issued April 1, 2009. At the time of the accident, total airframe time was about 1,584 hours. The most recent 100-hour/annual inspection was performed on May 1, 2012. Maintenance records showed that a 25-50-100 hour inspection was performed on May 1, which included checking torque of the aft pinion nut. The co-owner observed the mechanic perform that check. No logbook entry was required for this check under Part 91. A logbook entry dated March 9, 2012 noted replacement of an H-frame, which required exposure of pinion splines and a torque check of the aft pinion nut.
Meteorological Information
At 1151, Phoenix-Sky Harbor Airport reported wind 140 degrees at 9 knots, visibility 10 miles, few clouds at 20,000 feet, temperature 31°C. At 1153, Deer Valley Airport reported wind 170 degrees at 8 knots gusting to 20 knots, visibility 10 miles, sky clear, temperature 28°C.
Wreckage and Impact Information
The airframe remained generally intact but with substantial damage. The right landing gear separated; both skid tubes fractured. The tailboom separated at the forward bulkhead due to compression fracture. Impact damage was consistent with a high vertical velocity, wings-level, nose-low impact with the roof, followed by a nose over into the yard and impact with a wall. Main rotor blades remained attached and intact. The green dot tail rotor blade was fractured at the outer end of the hub spline; the blue dot blade was intact. The tail rotor drive shaft (TRDS) was fractured about 6 inches behind the main gear box attach spline, with minor torsional indication. The forward portion of the TRDS included the aft pinion nut, a portion of the pinion, and driving spline. The main gearbox input pinion was fractured and separated through the threads of the aft thread area. The phenolic spacer was not secured by the cotter pin and was pressed into the pinion's hollow interior. The engine sustained minimal damage; local law enforcement reported it remained running after the accident.
Tests and Research
Components including the main transmission pinion, aft pinion nut, tail rotor drive shaft section, driving spline, phenolic plug, and forward bump stop were examined at the NTSB Materials Laboratory. The driving spline exhibited fretting wear and material loss up to 50% of cross-sectional area on outer teeth. The pinion fractured transversely while fastened inside the aft pinion nut. Fracture surface analysis revealed progressive fatigue cracking initiating at a thread root, with multiple crack initiations. No material deficiencies were found.
A Sikorsky accident investigator reported improper assembly: the phenolic pinion plug was not properly installed, the split bushing was missing, and an incorrect longer spline adapter was installed on the tail transmission. Examination of the GPS unit showed recorded points did not capture the accident flight.