Flight History
On May 11, 2010, at about 1335 eastern daylight time, a Bell 407 helicopter, registration N31VA, operated by the Virginia State Police, made an emergency landing after an engine failure and autorotation near Virginia Highlands Airport (VJI) in Abingdon, Virginia. The crew, consisting of a certificated flight instructor (CFI) and a commercial pilot, both Virginia State Police officers, were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the public use instructional flight.
The flight was intended for aircraft orientation training for the pilot. After one takeoff and landing at VJI, the helicopter proceeded northwest to practice confined area operations at a field about 3 miles from the airport. En route, the crew heard a low growl from the engine compartment. Approaching the field at an altitude of about 250 feet above ground level and 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 took control, initiated a 180-degree right turn, and performed an autorotation to the field. At about 50 feet, the CFI flared and landed. The helicopter bounced once and came to rest on a slight slope, with the right skid on the uphill side. The crew shut down and exited normally. The flight duration was seven minutes.
Aircraft and Engine Information
The Bell 407 was manufactured in 2000 and first registered to the Commonwealth of Virginia in January 2001. It was equipped with a Rolls-Royce 250-C47B engine. Maintenance records showed a most recent annual inspection in October 2009, a 50-hour/3-month airframe inspection on April 20, 2010, and a 150-hour engine inspection the following day. At that time, the aircraft total time was about 3,887 hours, engine total time about 3,689 hours, and the engine had 6,631 cycles. The helicopter and engine accumulated about 14.5 hours between those inspections and the accident.
Wreckage and Examination
Post-accident examination revealed both landing skids splayed outboard, with the right skid more deformed. The upper 3 inches of the left vertical stabilizer were 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 turret mounted under the left rear seat penetrated the cabin floor, and the Night Sun lamp under the left front seat was damaged but did not penetrate. Control continuity was confirmed.
The engine was found securely in position with all hardware in place. Visual inspection showed no external damage. Motoring the engine to about 10% rpm resulted in smooth rotation from starter generator to compressor. Rotation of the main rotor head showed smooth rotation to the No.4 power turbine wheel. No engine start was attempted.
Engine Data and Detailed Examination
The electronic control unit (ECU) was equipped with non-volatile memory units: a maintenance terminal and an incident recorder. Data download revealed two engine surge events captured in the Last Engine Run Fault section. Accumulated faults showed one gas temperature exceedance of 1,712.9°F for 1.25 seconds, which the Rolls-Royce representative believed likely occurred during the engine anomaly.
On June 10, 2010, a detailed engine examination at the Rolls-Royce facility was attended by an FAA inspector and representatives of Rolls-Royce, Virginia State Police, and Bell Helicopter. The compressor module showed no damage and operated smoothly. The gearbox interior contained clean oil. Disassembly revealed a metal strip about 2 inches long lodged between the basket and inner wall of the outer combustion case. A second similar strip was bent around and lodged in a dilution hole of the combustion liner. The support plate (deflector plate) normally located at the aft end of the combustion liner was absent.
The turbine module exhibited heavy metallic spatter across the aft face of the No.1 nozzle shield and a yellow substance smeared around its outer rim. A foreign metal strip was found bent around a first stage nozzle vane saddle. The No.1 nozzle showed discoloration from thermal exposure. Several turbine vanes and the No.1 turbine wheel had foreign object impact damage. All turbine blades were damaged, with four missing most of their airfoil length. The No.2 turbine wheel had metal spatter and impact damage; its nozzle had nicks and thermal damage on about 20% of vane trailing edges. The lower chip detector was clear; the upper chip detector had light metallic particles.
Combustion Liner History and Repair
The combustion liner (part number 23064570, serial number PHI-0020) was originally manufactured by Rolls-Royce. In 2008, it was sent to Cadorath Aerospace Lafayette LLC (CAL LLC), a Rolls-Royce authorized repair facility, for inspection and possible overhaul. The repair facility's traveler document indicated the liner was received, visually inspected, and rejected due to cracks in the liner and deflector plate. Attempts to weld-repair those cracks were unsuccessful. The document noted that the liner was partially disassembled, a new deflector plate and spacers were installed, and the liner was reassembled. In October 2009, when the engine had 3,544.9 hours total time, the original combustion liner was removed and the overhauled liner installed.
Failure analysis revealed that the required circumferential fillet weld between the liner and deflector plate was absent; only plug welds were present. The engine manufacturer's maintenance documentation did not authorize replacement of the deflector plate as a separate procedure; the repair facility was not authorized to conduct that procedure and lacked applicable guidance. The investigation could not determine how or why the repair facility replaced the deflector plate and then approved it for return to service on October 24, 2008. At the time of failure, the liner had accumulated 158.4 hours since installation.
No evidence indicated that the repair facility or the FAA principal maintenance inspector was aware of the unauthorized repair. On December 21, 2010, after being advised of the failure mode, the repair facility issued a recall notice for 19 suspected improperly repaired units. On March 24, 2011, the engine manufacturer sent a letter of finding to the repair facility, detailing the deficiencies and instructing them to cease such repairs and recall affected liners. The repair facility confirmed all 19 liners were recalled by April 18, 2011.