ERA10TA261

The improper repair of an engine component by a repair facility, which resulted in a complete loss of engine power. Contributing to the accident was the failure of the repair facility to recognize that an improper repair had been accomplished, which allowed the component to be placed into service.

The certified flight instructor (CFI) was providing aircraft orientation training for the commercially rated pilot. Visual meteorological conditions prevailed and no flight plan was filed for the public aircraft flight. About 7 minutes into the flight, while enroute to practice confined area operations at a field about 3 miles from the helicopter base, the crew heard an unusual noise from the engine compartment. About 250 feet above the targeted field, the crew heard a louder noise, and the engine surged twice before ceasing to develop power. The CFI then conducted an autorotation to the sloping terrain below. The helicopter sustained substantial damage, which included fuselage crushing and the partial loss of one vertical stabilizer. Data downloaded from the engine control unit revealed an overtemperature fault indication; the engine was then removed and shipped to the engine manufacturer's facility for a detailed examination. A circular metal deflector plate, which was normally affixed to the aft end of the combustion chamber liner, was found fragmented in the turbine section. The turbine blades and vanes exhibited significant damage, which resulted from the deflector plate's release into the gas path. Metallurgical analysis of the combustion chamber liner revealed that the required circumferential fillet weld between the liner and the deflector plate had not been performed; only the preliminary positioning welds attached the deflector plate to the liner, and those welds failed during normal engine operation. Maintenance records indicated that the liner had accumulated about 158 hours in service since its overhaul and reinstallation. The liner overhaul included replacement of the deflector plate; the replacement was accomplished by a repair facility that was not authorized to conduct that procedure and that also did not possess the applicable guidance. The investigation was unable to determine the specifics of why the repair facility replaced, inspected, and approved the deflector plate. Although 19 months had transpired between the improper repair and the liner's failure, the investigation did not locate any information that indicated that either the repair facility or the Federal Aviation Administration principal maintenance inspector for the repair facility was aware that maintenance personnel at the repair facility had accomplished a procedure that it was not authorized to conduct. The repair facility identified 19 other assemblies that had a known or suspected improper repair, recalled those assemblies, and no additional in-service failures occurred. The engine manufacturer subsequently modified its overhaul manual to clarify the relevant repair and replacement procedures.

HISTORY OF FLIGHT On May 11, 2010, about 1335 eastern daylight time, a Bell 407 helicopter, N31VA, operated by the Virginia State Police, was substantially damaged during an emergency landing following an engine failure and autorotation near Virginia Highlands Airport (VJI), Abingdon, Virginia. The certificated flight instructor (CFI) and the commercial pilot were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the public use instructional flight. According to the crew, who were both Virginia State Police (VSP) officers, they and the helicopter were based at VJI. The purpose of the flight was to provide aircraft orientation training for the pilot. The pilot conducted one takeoff and landing at VJI, and then proceeded to the northwest to practice confined area operations at a field about 3 miles from VJI. When the flight was enroute to the practice field, the crew heard a noise that they described as a "very low growl" coming from the engine compartment. As they approached the field at an altitude of about 250 feet above ground level (agl) and a speed of 80 knots, they heard a "very loud growl," and the engine "surged" twice. The "FADEC DEGRADE" caution light illuminated, and an aural "ENGINE OUT" alert sounded. The CFI informed the pilot that he was taking control of the helicopter, and then initiated a 180 degree right turn, and an autorotation to the field. At about 50 feet agl, the CFI flared the helicopter, and then landed it. The helicopter bounced one time and came to rest on a "slight slope" in the field, with the right skid on the uphill side. The crew shut down the helicopter and exited normally. The pilot reported that the flight duration was seven minutes. Two days after the accident, the helicopter was recovered to a Bell Helicopter completion and maintenance facility. The engine, including the electronic control unit (ECU) and fuel control, was removed and shipped to the Rolls-Royce facility in Indianapolis, Indiana for detailed examination and testing. Since the helicopter was a public use aircraft, a week after the accident, the VSP formally requested that the Federal Aviation Administration (FAA) "conduct a formal investigation" into the accident. PERSONNEL INFORMATION Pilot and FAA records indicated that the CFI held an airline transport pilot certificate, with several ratings, including rotorcraft-helicopter, and a flight instructor certificate with rotorcraft-helicopter and instrument helicopter ratings. The CFI's most recent FAA second-class medical certificate was issued in July 2009, and his most recent flight review was completed in August 2008. He reported that he had 3,278 total hours of flight experience, which included 2,316 hours in helicopters, of which 1,100 hours were in the accident helicopter make and model. Pilot and FAA records indicated that the pilot held a commercial certificate, with several ratings, including rotorcraft-helicopter, and instrument helicopter. The pilot's most recent FAA second-class medical certificate was issued in April 2010. He reported that he had accumulated approximately 4,328 total hours of flight experience, which included 4,007 hours in helicopters, of which 147 hours were in the accident helicopter make and model. AIRCRAFT INFORMATION According to FAA records, the helicopter was manufactured in 2000, and was first registered to the Commonwealth of Virginia in January 2001. Examination of the maintenance records revealed that the records system utilized three separate hour-tracking categories, as well as an engine "cycles" value. The three hour-tracking categories were "Hobbs," "Aircraft TT (total time)," and "Engine TT." Examination of the records from October 2009 to the date of the accident indicated a constant difference between the aircraft and engine TT values; the aircraft TT value was 198.0 hours more than the engine TT value. In contrast, the Hobbs value did not maintain a constant difference from those values, but was about 43 hours more than the aircraft value. The helicopter was equipped with a Rolls-Royce 250-C47B engine. According to the maintenance records, the most recent annual inspection was completed in October 2009. The most recent 50 hour/3 month airframe inspection was completed on April 20, 2010, and the most recent 150 hour engine inspection was completed the following day. As of those two latter inspections, the aircraft TT was about 3,887 hours, the engine TT was about 3,689 hours, and the engine had accumulated 6,631 cycles. The helicopter and engine accumulated about 14.5 hours between those inspections and the accident. METEOROLOGICAL INFORMATION The VJI 1343 recorded weather observation included wind from 200 degrees at 10 knots, with gusts to 18 knots, visibility 10 miles, scattered clouds at 3,700 feet agl, broken cloud layers at 4,200 and 5,000 feet agl, temperature 21 degrees C, dew point 12 degrees C, and an altimeter setting of 30.20 inches of mercury. WRECKAGE AND IMPACT INFORMATION Representatives from the FAA and Rolls-Royce arrived at the accident scene the day after the accident. They reported that both landing skids were splayed in the outboard direction, and that the right skid exhibited more deformation than the left skid. The upper 3 inches of the left vertical stabilizer was missing, and one main rotor blade had paint transfer marks consistent with stabilizer contact. The tail skid and tail rotor blades were intact. The forward-looking infrared (FLIR) turret that was mounted on the underside of the fuselage below the left rear seat was pushed up, and penetrated the cabin floor. The "Night Sun" lamp that was mounted on the underside of the fuselage, below the left front seat, was damaged, but did not penetrate the cabin. The remainder of the airframe, main rotor and tail rotor were otherwise intact. Movement of cockpit controls confirmed continuity to all control surfaces. The helicopter had approximately 790 pounds of fuel on board at the time of the event. All fuel, lubrication, and pneumatic lines were checked for damage, continuity and security; all were intact. The engine was found securely in position, with all attaching hardware in place and secure. A visual inspection of the engine exterior did not reveal any damage. Checks were then made of the N1 and N2 drive trains. Motoring of the engine to approximately 10 percent rpm resulted in smooth and continuous rotation from the starter generator to the compressor. Rotation of the main rotor head showed resultant smooth and continuous rotation to the No.4 power turbine wheel. No attempt to start the engine was made. ADDITIONAL INFORMATION Engine Data Recorder According to the Rolls-Royce representative, the ECU was equipped two separate non-volatile memory (NVM) units, known as the "maintenance terminal" (MT), and the "incident recorder" (IR). The MT recorded discrete events relevant for maintenance purposes, and the IR recorded time history data of engine parameters. The IR recording was designed to start whenever a "trigger" (parameter exceedance) was detected; the recording would capture data from 12 seconds prior to the trigger, and continue after the trigger. Visual examination of the ECU found it to be securely in position, with its data connectors in place. The ECU NVM data were downloaded. Examination of the data revealed that two "engine surge" events were captured in the "Last Engine Run Fault" section of the recording. Also, the "Accumulated Faults" data revealed only one temperature exceedance. That value was a gas temperature exceedance of 1.25 seconds duration, with a maximum temperature of 1,712.9 degrees F. The exceedance did not have a time-of-occurrence associated with it, but it was the opinion of the Rolls-Royce representative that it most likely occurred during the engine anomaly/fault event. The Rolls-Royce Maintenance Manual (MM, Sec 72-00-00 p