N17754

HISTORY OF FLIGHTOn September 18, 2000, at 0815 hours mountain standard time, a Sikorsky/Orlando S-55 helicopter, N17754, landed hard following a loss of engine power, about 4 miles east of Hoover Dam, Arizona. During the forced landing, the airline transport pilot and six passengers received minor injuries. The helicopter was substantially damaged. The helicopter was being operated by Papillon Grand Canyon Helicopters, under 14 CFR Part 135, as a sightseeing flight. A company visual flight rules flight plan was filed. Origination of the flight was Las Vegas, Nevada, about 0730, and it was destined for the Grand Canyon, Arizona.

The pilot reported that all aircraft and engine instruments, and flight indications, had been normal. About 20 minutes into cruise flight, about 3,000 feet mean sea level (msl), the engine and rotor noise suddenly decreased, and the helicopter began a descent. There were no accompanying warning lights illuminated. The pilot reduced the collective and verified the control positions. A forced landing was initiated in unfavorable terrain. PERSONNEL INFORMATIONAccording to the operator, the airline transport rated pilot had accrued a total flight time of 7,372 hours, with 266 hours in the accident helicopter, and 7 hours in the last 24 hours. AIRCRAFT INFORMATIONThe helicopter was fabricated from an ex-military, remanufactured, and modified Sikorsky S-55 (UH-19D). The original radial reciprocating engine has been replaced with a Garrett Gas Turbine TPE 331, modified to a TSE 331 IOUA 511SW. It had a 6,000-hour time between overhaul. According to aircraft maintenance log information on January 10, 2000; engine serial Number P-03445C was removed at 114.1 hours and engine serial Number P-03604C was installed.

According to maintenance records dating back to July 3, 1985, the accident engine P-54083 operated in more than one Fairchild SA226 airplane in Australia, and several rotary wing S-55 aircraft during certification of the helicopter in the United States.

The accident helicopter was issued an experimental special airworthiness certificate on July 17, 1998, by a Federal Aviation Administration (FAA) DAR. Operating limitations stated that the helicopter was to be operated for at least 2 hours with at least three takeoffs and landings to a full stop before certification. The flights were to be conducted in the geographical location and over sparsely populated areas. According to the initiating paperwork, the aircraft, Hobbs meter, and cycles started at zero hours.

On July 18, 1998, an application was made for a standard airworthiness certificate. The FAA DAR issued the standard certificate on the same date. Again on the same date, the FAA DAR with aircraft operating limitations in multiple category issued a standard or restricted special airworthiness certificate.

An application was made for a special airworthiness certificate in the experimental category on July 30, 1998, for research and development. An FAA Flight Standards District Office (FSDO) aviation safety inspector issued the certificate. The paperwork indicated 2.0 total flight hours. The certificate was good for 1 year and was restricted to a 25-mile radius of Sanford Airport, Orlando, Florida.

A renewal of the experimental certificate was requested on July 28, 1999, listing 49.9 total flight hours. The purpose was to show compliance with the regulations and was signed by an FAA DAR.

On January 4, 2000, another renewal request was made for the same purpose listing 113.5 total flight hours and 63.6 since the last certificate issuance.

On January 9, 2000, an avionics installation was documented on an FAA form 337 by Papillon Airways, Inc., Grand Canyon, at 170.2 total flight hours. The form was date stamped by the Las Vegas FSDO March 2, 2000.

January 12, 2000, a multiple category airworthiness certificate for standard or restricted was requested and issued on that date, at 115.1 total flight hours.

July 5, 2000, Vertical Aviation Technologies, Inc., Sanford, Florida, issued an FAA form 337 for an airframe repair. An FAA inspector from that area field approved the repair.

The helicopter was added to the Papillon 14 CFR Part 135 certificate on August 2, 2001, at an unknown time. AIRPORT INFORMATIONThe helicopter was fabricated from an ex-military, remanufactured, and modified Sikorsky S-55 (UH-19D). The original radial reciprocating engine has been replaced with a Garrett Gas Turbine TPE 331, modified to a TSE 331 IOUA 511SW. It had a 6,000-hour time between overhaul. According to aircraft maintenance log information on January 10, 2000; engine serial Number P-03445C was removed at 114.1 hours and engine serial Number P-03604C was installed.

According to maintenance records dating back to July 3, 1985, the accident engine P-54083 operated in more than one Fairchild SA226 airplane in Australia, and several rotary wing S-55 aircraft during certification of the helicopter in the United States.

The accident helicopter was issued an experimental special airworthiness certificate on July 17, 1998, by a Federal Aviation Administration (FAA) DAR. Operating limitations stated that the helicopter was to be operated for at least 2 hours with at least three takeoffs and landings to a full stop before certification. The flights were to be conducted in the geographical location and over sparsely populated areas. According to the initiating paperwork, the aircraft, Hobbs meter, and cycles started at zero hours.

On July 18, 1998, an application was made for a standard airworthiness certificate. The FAA DAR issued the standard certificate on the same date. Again on the same date, the FAA DAR with aircraft operating limitations in multiple category issued a standard or restricted special airworthiness certificate.

An application was made for a special airworthiness certificate in the experimental category on July 30, 1998, for research and development. An FAA Flight Standards District Office (FSDO) aviation safety inspector issued the certificate. The paperwork indicated 2.0 total flight hours. The certificate was good for 1 year and was restricted to a 25-mile radius of Sanford Airport, Orlando, Florida.

A renewal of the experimental certificate was requested on July 28, 1999, listing 49.9 total flight hours. The purpose was to show compliance with the regulations and was signed by an FAA DAR.

On January 4, 2000, another renewal request was made for the same purpose listing 113.5 total flight hours and 63.6 since the last certificate issuance.

On January 9, 2000, an avionics installation was documented on an FAA form 337 by Papillon Airways, Inc., Grand Canyon, at 170.2 total flight hours. The form was date stamped by the Las Vegas FSDO March 2, 2000.

January 12, 2000, a multiple category airworthiness certificate for standard or restricted was requested and issued on that date, at 115.1 total flight hours.

July 5, 2000, Vertical Aviation Technologies, Inc., Sanford, Florida, issued an FAA form 337 for an airframe repair. An FAA inspector from that area field approved the repair.

The helicopter was added to the Papillon 14 CFR Part 135 certificate on August 2, 2001, at an unknown time. WRECKAGE AND IMPACT INFORMATIONThe Safety Board investigator did not inspect the wreckage at the accident site, but subsequently viewed it after recovery at a storage area in Phoenix, Arizona. ADDITIONAL INFORMATIONThe wreckage was released to the insurance company representative on September 20, 2001. TESTS AND RESEARCHThe accident engine, serial number P-54083C, was shipped to National Flight Services, Inc., Indianapolis, Indiana, for examination and functional testing. The engine was examined externally with minor repairs or replacements made prior to attempting a test cell run.

The engine started and idled normally. Increasing the rpm to the certified operating specification of 101.5 percent revealed no abnormal conditions. The test propeller was moved from the start locks and an increasing torque load was applied. As the torque was increased the engine responded normally until approximately 60 percent torque when indicated engine rpm rapidly decreased and an emergency shutdown was initiated.

The process was repeated through 12 cycles, during which the indicated rpm began a sudden rapid decrease when torque was increased. Test cell troubleshooting failed to identify or correct this condition. During manual rotation of the propeller following the final cycle some "slipping" was noted between the output shaft and the main rotating group. Subsequent examination of the gearbox revealed disengagement of the sun and bull gear assembly.

The examination revealed fretting damage to the retaining nut and mating surfaces. Visual examination of the sun and bull gears revealed severe damage to the mating splines of both gears. The gears were determined to be of an early design, and not in compliance with a manufacturer and modifier recommended service bulletin (TPE331-72-0606) to replace them.

According to the attached engine examination report: "elevated iron concentration in oil samples, discoloration of engine oil, staining of the mating surfaces and chip detector illumination prior to this incident were indications of excessive fretting of the internal splines."

Prior to departure from Las Vegas, during preflight checks, the engine chip warning light illuminated. Maintenance personnel removed, cleaned, and reinstalled the chip light sensor, and the helicopter departed after ground checks. A similar event occurred about 64 hours prior, and maintenance reported a little bit of "fuzz" and no slivers. No additional checks were performed.

Examination of past oil analysis samplings revealed increases of iron and magnesium over a period of time, with analysis report comments of "Alert" and "Iron Appears High." Analysis report copies are attached.