CHI95LA160

A witness who occasionally saw the airplane during its turn to reverse direction reported that he heard a loud 'pop' shortly after the engine suddenly stopped running. The engine examination revealed a free wheeling supercharger impeller. The collector drive floater gear had 4 1/2 teeth missing. Metal chips were detected in the oil screen. The gear teeth from the floater gear were found in the sump and engine's crankcase housing. A borescope inspection of the engine's cylinders revealed operation with a rich mixture. Sudden stoppage of the impeller would not result in the gear teeth's location noted above. Missing gear teeth could also interrupt engine power. The NTSB metallurgical laboratory's findings on the separated gear teeth and floater gear revealed overstress separation of the gear teeth.

On May 30, 1995, at 1054 central daylight time, a Weatherly 201C, N9038W, operated by the Platte Valley Aerial Spraying, Incorporated, of Clarks, Nebraska, and piloted by a commercially certificated pilot, was destroyed during a collision with the ground during maneuvering to begin another aerial application swath run. Visual meteorological conditions prevailed at the time of the accident. The pilot was fatally injured. The 14 CFR Part 137 flight was not operating on a flight plan. The flight departed Clarks, Nebraska, exact time unknown.

One witness occasionally saw the airplane during its swath run turn around and related climb. During one of the times he was not looking at the airplane he said he heard the engine suddenly stop followed by a loud "pop."

The Federal Aviation Administration (FAA) Principal Maintenance Inspector (PMI) representing the NTSB on-scene reported no evidence of pre-impact airframe or flight control system failure. He said the engine had been involved in a post-impact fire that was limited to the front of the airplane.

The PMI stated N9038W's carburetor had no fuel in its float bowl. He said the carburetor had been in the post-impact fire. Fuel samples from the airplane were not obtained due to fuel tank rupturing when the airplane collided with the ground.

According to the PMI's report, N9038W's fuel tank selector was on the left fuel tank. The mixture control was "Full Rich" and the throttle was positioned at mid-range. The propeller control was found in the low RPM setting. N9038W's magnetos would not rotate due to collision damage. Steel particles were found in the engine oil screen. A collector drive floater gear (drive gear) tooth was found in the engine sump.

The engine's supercharger impeller drive was found free wheeling when external rotational force was applied to it. Examination revealed 4 1/2 teeth were missing from the drive gear. Three gear teeth from this gear were found in the engine's crankcase housing. A borescope inspection of the engine's cylinder's revealed evidence of "...operation under a rich mixture..." according to the PMI's report.

A representative from P&W stated the gear teeth damage was not from sudden stoppage due to the locations the teeth were found. He said that power interruption could be caused by the teeth breaking away from the drive gear.

Discussion with an FAA Certification Office propulsion engineer revealed that a rich mixture indication found in the engine's combustion chamber would show that the supercharger was not operating adequately. Examination of the super charger's collector drive floater gear unit and separated teeth showed "...typical... overstress separations," according to the NTSB Metallurgical Laboratory.

N9038W's engine logbook showed its major overhaul was completed on February 6, 1990. The last entry in the logbook, February 2, 1995, showed it had 752.92 hours of running time since it had been overhauled. No other engine operating time since overhaul records were found. According to the overhaul records, the engine's collector drive floater gear passed its magnetic inspection on January 29, 1990.

Fuel samples taken from the fuel tank used to fuel N9038W were examined by Petrl Laboratories in Indianapolis, Indiana. The fuel sample examined meets all ASTM specifications for 100LL aviation fuel (ASTM D-910, Detailed Requirements for Aviation Gasoline). Excerpt's from that report are appended to this report.

An autopsy was conducted by Pathology Medical Services, P.C. of Lincoln, Nebraska. The toxicology report from the FAA Civil Aeromedical Institute was negative for drugs, alcohol, cyanide, and carbon monoxide.