History of Flight
On July 26, 2014, at approximately 1545 eastern daylight time, a Hiller UH-12E helicopter, registration N107HA, was substantially damaged when it impacted terrain near Wadesboro, North Carolina. The airline transport pilot was not injured. Day visual meteorological conditions prevailed and no flight plan had been filed. The local aerial application flight originated from a temporary staging location about 1540. The flight was conducted under 14 Code of Federal Regulations Part 137.
According to the pilot, while applying agricultural product at about 75 feet above ground level, he heard three engine compressor stalls followed by a partial loss of engine power. During a forced landing to a nearby road, the helicopter rolled over into a drainage ditch and came to rest on its right side, resulting in substantial damage to the fuselage, tailboom, main rotor blades, and tail rotor blades.
Personnel Information
According to Federal Aviation Administration (FAA) records, the pilot held an airline transport pilot certificate with ratings for airplane multiengine land and helicopter, a commercial pilot certificate with ratings for airplane single-engine land and instrument helicopter, and a flight instructor certificate for helicopter and instrument helicopter. He held an FAA second-class medical certificate issued on April 9, 2014. The pilot reported 9,604 hours of total flight experience, with 5,800 hours in rotorcraft and 1,210 hours in the accident helicopter make and model.
Aircraft Information
The helicopter received a standard airworthiness certificate on June 7, 1974. The most recent 100-hour inspection was conducted on June 18, 2014, at which time the helicopter had approximately 11,884 total hours in service. The helicopter was powered by an Allison 250-C20B turboshaft engine, manufactured on April 11, 1980. The engine had accumulated 7,566.6 total hours at the time of the accident.
Maintenance records indicate the engine was converted from a 250-B17C to a 250-C20B in September 1993, with 1,381.4 total hours at conversion. An entry in the gearbox assembly service record dated October 30, 2007, stated "repair after hard landing." The gearbox repair was completed on November 8, 2008, with no other entries revealing time in service between repair and installation on the accident engine. The compressor, gearbox, and turbine assemblies were installed on the accident engine on December 16, 2013, and the engine was installed on the helicopter the following day.
At installation, the engine had 7,474.4 total hours, the compressor had 5,651.9 total hours and zero hours since overhaul. On May 30, 2014, the gearbox was removed with a maintenance record entry indicating it was "making metal" and that "bearings on N2 tach/gov spur gear shaft going bad." The storage method for assemblies and engine prior to installation could not be determined.
Meteorological Information
The 1553 recorded weather observation at Monroe Airport (EQY) in Monroe, North Carolina, located about 22 nautical miles northwest, included wind from 210° at 6 knots, 10 statute miles visibility, scattered clouds at 4,200 feet, temperature 31°C, dew point 21°C, and an altimeter setting of 29.99 inches of mercury.
Wreckage and Impact Information
According to photographs provided by an FAA inspector, the helicopter came to rest on its right side in a ditch along a roadway perpendicular to the field being sprayed. The tailboom showed damage consistent with being severed by the main rotor blades, the skids were separated by impact, and the windscreen was damaged.
Test and Research
On October 7, 2014, the engine was examined at the manufacturer's facility. All fittings were secured with torque stripes showing no rotation evidence. Compressed air testing revealed an air leak at the B-nut on the Pc line, but the manufacturer stated it would not have precluded normal operation. The compressor was separated, and shims measured matched vibropeened numbers. After case separation, the N1 rotated with tactile and audible resistance, while N2 rotated smoothly.
The accessory gearbox was disassembled; bearings and transfer tube were PMA parts. The No. 2 bearing was examined in place; upon removal, the inner race separated and three ball bearings were found outside the race. The No. 2 bearing and hardware were sent to the NTSB Materials Laboratory.
NTSB Materials Laboratory examination of the No. 2 bearing revealed discoloration consistent with heat damage, a cage fractured in multiple locations with fatigue fracture features, outer race fretting damage and coked oil spray patterns, the compressor-side inner race half uniformly black and darker than the other half, outer race circumferential sliding contact marks, and bearing balls black, undersized per engineering drawings, with material loss signatures.
Further details of the engine disassembly and examination are available in the engine examination report in the public docket.