FTW96IA248

The airplane experienced an uncommanded shut down of the right engine during initial climb to altitude. An emergency was declared, and an uneventful single engine landing was made at the departure airport. Subsequent to the incident, metallic chips were found on the chip detector. The bearings of the accessory gear housing assembly (P/N 3103601-6) was missing all of the balls. Fragments of these ball bearings were found in the bottom of the engine case. Examination of the bearing races revealed pitting and scoring. According to the operator's diagnostics, the disintegration of the bearings allowed the gear shaft to drop down and contact the gears of the accessory drive idler gear assembly. Subsequently, the fuel pump drive gear was not driven, causing the engine to be starved of fuel. Inspection of the idler gear assembly revealed sheared gear teeth. Examination of the gearbox oiling system, revealed no evidence of failure or thermal distress prior to the initial bearing failure. The engine manufacturer had recently issued Service Bulletins addressing the installation of heavier duty gear assemblies in applicable engine installations.

On June 11, 1996, at 1835 central daylight time, a Fairchild SA-227DC, N850LS, experienced an uncommanded shutdown of the right engine during initial climb to altitude after takeoff from Woodring Field, Enid, Oklahoma. Operated by Lone Star Airlines as a Title 14 CFR Part 135 scheduled passenger commuter flight, the airplane was en route to Dallas, Texas. The airline transport pilot-in-command, first officer, and 6 passengers were not injured, and the airplane was not damaged during an emergency landing at Enid. The airplane was airborne approximately 5 minutes prior to the engine shutdown and visual meteorological conditions prevailed.

In an interview with the investigator-in-charge, the operator stated that after normal systems checks, flight Number 1264 taxied for departure at 1828 and took off at 1830. Engine indications were "normal" during take off and no water injection was utilized. Passing through 5,000 feet MSL, the chip detector light for the Number 2 engine illuminated. The flight crew then followed flight manual procedures for the chip detector light illumination, which were to monitor engine instruments, and if secondary indications manifested, to shut the engine down. After no secondary indications were observed, and company base operations was notified of a potential return, the captain elected to proceed with the flight. Approximately one minute after the call to base, the crew observed a rise in oil pressure for the #2 engine. While the crew commenced the checklist for a precautionary engine shut down, the engine lost power. An emergency was declared, and the aircraft made an uneventful single engine landing at the departure airport. The total flight time from initial take off emergency landing was 14 minutes.

Subsequent to the incident, the Number 2 engine nose case and gearbox diaphragm were removed by the operator for inspection after metallic chips were found on the chip detector. The bearings of the accessory gear housing assembly (P/N 3103601-6) was missing all of the balls. Fragments of these ball bearings were found in the bottom of the engine case. Examination of the bearing races revealed pitting and scoring. According to the operator's diagnostics, the disintegration of the bearings allowed the gear shaft to drop down and contact the gears of the accessory drive idler gear assembly. Subsequently, the fuel pump drive gear was not driven, causing the engine to be starved of fuel. Inspection of the idler gear assembly revealed sheared gear teeth. Examination of the gearbox oiling system, revealed no evidence of failure or thermal distress prior to the initial bearing failure.

The operator reported that a similar accessory drive bearing failure (same part number, 3103601-6) involving another Lone Star Metro 23, N853LS, occurred on May 25, 1996. According to maintenance records, the total time in service of the failed bearing on N853LS was 4,444 hours. The total time in service of the failed accessory drive bearing from N850LS, was 4,451 hours.

Due to the similar hours in service of the aforementioned bearing failures, service difficulty reports (SDR's) were researched for TPE331-12/12B series engine reduction gear and shaft sections that had accessory drive bearings (P/N 3103601-6) installed. According to SDR data from January 1, 1990 through June 20, 1996, there were twenty-six reported removals of reduction gear assemblies due to accessory drive bearing, P/N 3103601-6 problems. A statistical summary of the removals referencing the mode of problem detection revealed the following:

Fourteen(54%) were removed due to scheduled oil analysis program (SOAP) & filter detection. Nine(34%) were removed due to in-flight shutdowns (manual or uncommanded). Two(9%) were removed due to chip detector warnings. One(2%) was removed due to grinding noises heard.

The manufacturer concurred with the SDR information. According to the manufacturer, during the same time period of the twenty-six removals, all reduction gear and shaft sections with P/N 3103601-6 installed, had a cumulative time in service of approximately 4.2 million hours (900,000 hours per year).

At the time of the incident, the manufacturer had two service bulletins in draft which addressed the replacement of accessory gear assemblies with bearing P/N 3103601-6 installed, with heavy duty bearings to increase dependability and service life. Both bulletins outlined the replacement of accessory gear assembly, P/N 3103601-6, and (compressor) bearing retainer assembly, P/N 3103903-1, with accessory gear assembly, P/N 3103977-3. The bulletins applied to TPE331-12 and TPE331-12B engine installations. Service Bulletin A72-0989, applicable to TPE331-12B engine installations in the single engine configured aircraft, was categorized as an "Alert" Service Bulletin, Category 1, Safety. Service Bulletin 72-0997, applicable to TPE331-12 engine installations in multi-engine configured aircraft, was categorized as a Service Bulletin, Category 1, Safety.

In dialog with the manufacturer, this office discussed the possibility of applying the "Alert" status to Service Bulletin 72-0997, applicable to the multi-engine installations of TPE331-12 model engines.

Correspondence received by this office from the manufacturer on January 30, 1997, stated that Service Bulletin 72-0997 will become an "Alert" status bulletin in February, 1997.