WPR12FA191

A loss of tail rotor drive due to a fatigue failure of the main transmission pinion, which resulted in a loss of directional control during cruise flight.

When the pilot was about 2 minutes from reaching his destination at an altitude of about 500 feet above ground level (agl), he detected a vibration coming from the back of his seat and in the anti-torque pedals. This was followed by a right yaw that was not correctable with pedal input. As the pilot attempted to maintain level flight he heard a "metallic clunking" behind him. He then looked over his shoulder and saw what he thought was the tail rotor slowing down. Able to maintain forward flight by countering the right yaw with left cyclic input, the pilot located a cul-de-sac in a residential neighborhood in which to land. He lowered the collective, rolled off throttle, and made a slight right turn toward the cul-de-sac. During the landing the helicopter impacted the roof of a house, then a brick wall that separated the house from the adjoining residence. The helicopter came to rest in the backyard of the adjacent home. Witnesses reported that the helicopter didn't sound right, that the engine was sputtering, and that its speed was increasing and decreasing. It was observed rocking and teetering, and then nose-dived toward the ground. After the helicopter crash landed, the engine continued to run and the tail rotor continued to spin. A post-accident investigation revealed that the main transmission pinion had failed from fatigue. Subsequent to the fracture of the main transmission pinion, the tail rotor drive shaft would have been free to move, resulting in the loss of the tail rotor drive. Maintenance records revealed that the main transmission pinion was part of a periodic inspection check, which was completed the day prior to the accident.

HISTORY OF FLIGHT On May 2, 2012, about 1140 mountain standard time, a Hughes 269C helicopter, 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, and a flight plan was not filed. The local flight departed Deer Valley Airport (DVT), Phoenix, Arizona, about 1115. In a telephone conversation with the pilot, as well as in a statement submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that after picking up his passenger/photographer, he departed DVT for the construction site the photographer had been hired to photograph. The pilot stated that after taking off he proceeded southwest toward the construction site about 500 feet above ground level (agl) and at an airspeed of between 70 to 75 knots. The pilot stated that about 2 minutes prior to reaching the construction site he detected a vibration in the back of his seat, as well as in the anti-torque pedals. This was followed immediately by a right yaw that was not correctable with pedal input. The pilot opined that he attempted to maintain level flight, then heard a "metallic clunking" sound behind him. He then looked over his left shoulder and thought he observed the tail rotor slowing down. He said he was still maintaining forward flight at about 70 knots and was maintaining his forward track by countering the yaw with left cyclic input. The pilot stated that he picked out a residential area with a cul-de-sac street, and elected to autorotate to the street. He reported that he lowered collective, rolled off the throttle to the idle detent, and made a slight right turn toward the cul-de-sac, maintaining about 55 knots during the autorotation. The helicopter initially impacted the roof of a house and a brick wall that separated the house from the adjoining residence. He said the helicopter came to rest in the backyard of the adjacent house in a slightly nose down, upright attitude. The pilot reported that the main and tail rotor blades were intact, and that in his view this was a mechanical failure rather than a loss of tail rotor effectiveness event. He also stated that [during the descent] the helicopter did not rotate about its vertical axis, that it did not spin, and that it was gusty with respect to the winds. Local law enforcement provided the IIC with statements of 3 witnesses who observed the accident. Witness #1, who was located at his residence about 1 block north of the accident site, reported that he heard the helicopter overhead, and that it "didn't sound right." The witness stated that the engine was sputtering and "sounded wrong," and as he watched it, it was "rocking" and "teetering." The witness added that it then lost altitude and nose-dived toward the ground south of his location. Witness #2 reported that he was in an alley south of the street where the helicopter crash landed, and when he [first] heard the helicopter "it did not sound right." The witness stated that the engine was "sputtering", the rpms were increasing and decreasing, and that the main rotor blade was also increasing and decreasing in speed. The witness opined that the helicopter made a U-turn overhead while losing altitude, and that he lost sight of it due to trees and houses in the area. He then proceeded to the accident site and began turning all switches which were labeled ON and OFF to the OFF position, but the engine kept running. He also stated that the tail rotor blades were moving very fast. Witness #3, who was a co-worker of witness #2 and at the same relative location during the initial sighting of the helicopter, reported that he noticed the helicopter turning around and going lower, and that the engine didn't sound right, like it was just barely idling. He stated that the helicopter continued to lose altitude, and it became apparent that it was either going to land or crash. The witness added that after arriving at the accident site the engine continued to run for some time. He added that the tail rotor blades were spinning rapidly. PERSONNEL INFORMATION The pilot, age 40, possessed a commercial pilot certificate for rotorcraft-helicopter, and ratings for instrument helicopter and helicopter instructor. The pilot completed his most recent flight review on March 29, 2012. He was issued a second-class Federal Aviation Administration (FAA) airman medical certificate without waivers or limitations dated December 31, 2011. The pilot reported a total flight time of 1,460 hours, all in helicopters, with 1,030 hours in make and model, 1,410 hours as pilot in command, and 980 hours as pilot in command in make and model. Additionally, the pilot reported having given 950 hours of dual instruction, with 800 hours of dual instruction given in the accident make and model helicopter. The pilot revealed that he had flown a total of 90 hours, 30 hours, and 1 hour in the preceding 90 days, 30 days, and 24 hours respectively. AIRCRAFT INFORMATION The accident helicopter was a Hughes Model 269C, serial number 0694C, manufactured in 1978. Its most current airworthiness certificate was issued on April 1, 2009. At the time of the accident the helicopter had accumulated about 1,584 hours total airframe time, with a Hobbs Meter time of 899 hours. The most recent periodic 100-hour/annual inspection was performed on May 1, 2012. The previous periodic inspection encompassed 25-50-100-200-400 hour inspections, which were completed on March 29, 2012, at a total airframe time of 1,481.4 hours, with a Hobbs Meter time of 796.4 hours. The maintenance records revealed that the last annual inspection was completed on May 6, 2011, at a total airframe time of 981.6 hours. It was revealed during the investigation that during the periodic inspection conducted on May 1, 2012, which was the day prior to the accident, that a 25-50-100 hour inspection had been performed in accordance with the manufacturer's Helicopter Maintenance Instructions (HMI), which included the procedure for checking the proper torque of the aft pinion nut. The co-owner of Canyon State Aero reported to the IIC that he had personally observed the mechanic performed the torque check of the aft pinion nut. The aircraft maintenance logbook revealed no entry for this specific check, nor was one required under Federal Aviation Regulation (FAR) Part 91. Additionally, and while checklist sheets are available to follow and track such checks, they are not required to be completed or maintained under FAR Part 91. A maintenance logbook entry dated March 9, 2012 at 1,481.4 hours (100 hours prior to the accident) revealed that a replacement H-frame was installed in conjunction with a 100/400-hour inspection. A Sikorsky engineer reported that as a result of this inspection the pinion splines would have been exposed and that a torque check of the aft pinion nut would have been required. METEROROLOGICAL INFORMATION At 1151, the weather reporting facility at the Phoenix-Sky Harbor International Airport (PHX), Phoenix, Arizona, located about 4 nm south of the accident site, reported wind 140 degrees at 9 knots, visibility 10 miles, few clouds at 20,000 feet, scattered clouds at 25,000 feet, temperature 31 degrees Celsius (C), dew point 1 degree C, and an altimeter setting of 29.83 inches of mercury. At 1153, the weather reporting facility at the Deer Valley Airport (DVT), Phoenix, Arizona, located about 11 nm north of the accident site, reported wind 170 degrees at 8 knots, gusts to 20 knots, variable 130 degrees to 200 degrees, 10 miles visibility, sky clear, temperature 28 degrees C,