History of Flight
On March 3, 2009, at 1045 mountain standard time, a Eurocopter AS350 B2 helicopter, registration N197AE, sustained minor damage following a loss of engine power and subsequent forced landing near the Canyon West Airport in Peach Springs, Arizona. The helicopter was registered to XEBEC, LLC, and operated by Papillon Airways, Inc. under 14 Code of Federal Regulations Part 135. The commercial pilot and six passengers were not injured. Visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed for the air tour flight. The flight originated from Boulder City Airport, Nevada, at 1015.
The purpose of the flight was to transport passengers to a remote sightseeing area in the Grand Canyon. Approximately 30 minutes after departure, during descent to the landing area, the pilot heard a loud pop followed by a loss of main rotor RPM. The pilot transmitted a mayday call and performed an autorotation. While descending into a canyon, the pilot heard the loud pop and observed multiple warning lights on the instrument panel. After lowering the collective to regain rotor RPM, the pilot raised the collective to check for available power and heard a low rotor RPM warning horn a second time. He initiated an autorotation to a clear area and landed without further incident. After landing, the engine was not running, but the rotor blades were still turning.
Pilot Information
The 27-year-old pilot held a commercial helicopter pilot certificate with a helicopter instrument rating, as well as a flight instructor certificate with rotorcraft helicopter and instrument ratings. His most recent second-class medical certificate was issued on March 3, 2009, with no limitations. According to the operator, the pilot had accumulated approximately 1,968 total flight hours, with 503 hours in AS350 series helicopters.
Aircraft Information
The single-engine, seven-place helicopter was a Eurocopter AS350 B2 that had been converted to an AS350 “SD2” under Supplemental Type Certificate SR01647SE. This conversion included the installation of a Honeywell LTS101-700D-2 engine in place of the original Turbomeca Arriel 1D1 engine. The most recent maintenance on the engine was a 150-hour inspection on January 28, 2009. At that time, the engine had 8,319.9 hours since new, 2,095.9 hours since overhaul, 13,192.05 Ng cycles, and 9,279.25 Np cycles.
Engine Examination
The Honeywell LTS101-700D-2 turboshaft engine was removed and shipped to Honeywell Aerospace in Phoenix, Arizona, for examination under NTSB supervision. The engine was intact with nominal impact damage. Various airframe components remained installed. The power turbine rotated about 5 degrees by hand before binding; the gas producer shaft rotated freely. Rotational continuity was established through the power turbine accessories, accessory gearbox, and output shaft.
The gas generator module was intact. The compressor bearing retainer, number one bearing liner and seal rotor, compressor vane assembly, and axial compressor rotor were intact and undamaged. Black residue was observed on all axial compressor rotor blades. Evidence of oil was found near the compressor impeller hub inducer, and rub marks were present on the impeller blades. The compressor assembly shaft, impeller shroud, diffuser assembly, diffuser housing assembly, and gas producer turbine nozzle were intact and undamaged. Rotational score marks were noted at the impeller shroud inducer at the 11 o'clock position.
The number two roller bearing was intact and black, with some resistance when rotated. The number one ball bearing was intact, undamaged, and rotated freely; evidence of seal leakage was noted. Examination of the power turbine module revealed the rear bearing support housing intact with debris in the oil scavenge passage near the oil feed ring assembly. The oil sump area was black. The rear bearing support flowed approximately one-half of normal oil flow during testing, and irregular flow patterns were observed from the oil feed ring.
The combustor liner and power turbine nozzle assembly were intact, with rotational scoring on the nozzle assembly corresponding to the power turbine blades. The number three bearing spacer was undamaged. The oil feed ring assembly was intact and black, with debris adhering to it. Scoring was observed on the power turbine shaft corresponding to the number three bearing inner race; the shaft was discolored near the bearing.
Detailed Bearing and Oil System Findings
Number two roller bearing showed nominal mechanical damage; all components exhibited heat discoloration. Light, uniform wear and oil residue were present. The rear bearing support housing had no significant damage, but borescope examination revealed deposits consistent with coked oil in the oil passages feeding the oil supply ring and number three ball bearing.
X-ray examination of the oil feed ring showed a blockage in the main oil passage. A cross section revealed long, smooth flakes of black material near the aft end, blocking the inlets of the two aft oil jets that feed the number three ball bearing. Energy dispersive X-ray and infrared analysis indicated the flakes were most likely composed of coked synthetic oil.
The number three bearing inner race sections and balls exhibited rub-type damage, deformation, and heat-like discoloration. The outer race showed a zone of highly heat affected microstructure. Heat affected material from the balls and/or forward race was deposited on the outer race, aft inner race, and cage. No distinct oil residue was observed on the bearing components.
An Operating Information Letter issued by Honeywell International Inc. on January 30, 2009, specified that failure to follow the non-emergency engine shutdown procedure—including a 2-minute idle period and 10-second motoring after shutdown—could lead to coke buildup in the number two and three bearing oil jets and sump area, potentially resulting in bearing failure. The operator reported that company pilots were instructed to comply with the idle cool-down procedure, but company policy did not require the post-shutdown motoring due to operational concerns about oil depletion.