FLAGSTAFF, AZ, USA
N7188A
Cessna 172
The pilot stated that the preflight and run-up were conducted with no anomalies noted. After takeoff, the airplane experienced a loss of engine power followed by a loss of altitude and collision with terrain. The airplane came to rest inverted in a sewage pond near the airport. After the power loss, the pilot made an unsuccessful attempt to restart the engine utilizing the emergency checklist. The engine was inspected and mechanical continuity of the engine was established. The crankcase was separated and it was noted that the bearings, pistons, and cylinders exhibited heat discoloration. The number 4 main bearing exhibited evidence of rubbing on the crankshaft and a section of that bearing insert was severely worn, heat distressed, and had flowed over the edge of the crankcase bearing journal. The number 6 connecting rod bearing insert exhibited an unidentified metal substance in the oil port. The remaining crankcase oil journals were found to be clear. The oil pump was disassembled and revealed a nick on one of the driven gear teeth, which corresponded to circumferential scoring on the oil pump housing. The oil filter and suction screen were clean. No further discrepancies were noted with the engine. Review of the maintenance records revealed that an annual inspection, which included an oil change, had been completed approximately 1 hour prior to the accident flight.
On June 27, 1998, at 0605 hours mountain standard time, a Cessna 172, N7188A, experienced a loss of engine power after takeoff from runway 21 and came to rest inverted in a sewage pond near the Flagstaff Pulliman Airport, Flagstaff, Arizona. The aircraft, operated by the pilot/owner under 14 CFR Part 91, sustained substantial damage. The private pilot was not injured. Visual meteorological conditions existed for the local area personal flight and no flight plan was filed. In an interview with a Safety Board investigator, the pilot reported that the aircraft had been refueled with 36 gallons prior to the accident flight. He reported that he had completed the preflight inspection, which included visually checking the fuel level in the aircraft, and drained a fuel sample from both fuel sumps. He did not note any visual abnormalities with the fuel samples. The pilot stated that after he started the aircraft, he waited for ATIS information to be broadcast. He said that since the ATIS begins at 0600, and he was a few minutes early, the engine had ample opportunity to warm-up. The pilot reported that all systems were indicating normal, including the oil pressure and temperature, during his wait. After obtaining ATIS, he contacted ground control and requested a taxi clearance. The pilot performed a run-up, taxied to the departure end of runway 21, and requested takeoff clearance with closed traffic. During the initial climbout at 75 knots, aircraft performance began to deteriorate as the aircraft began losing airspeed and rpm's; although engine oil pressure remained in the green. Shortly after that, the propeller stopped. He switched the fuel selector from "both" to "left"; checked the throttle position, and richened the mixture in an attempt to restart the engine. The pilot reported that by this time his airspeed dropped to 60 knots and he was approximately 200 feet above ground level (agl). The airplane landed in the sewage pond and nosed over. The airplane was inspected on-scene by the general manager of the airport, who was interviewed by a Federal Aviation Administration (FAA) inspector. He stated that the quick release on the oil was found to be open and the engine was low on oil; however, an oil slick was present in the sewage pond. The general manager reported that the fuel system had not been compromised in the accident sequence, and the fuel tanks were full. He further reported that no fuel had spilled out into the sewage pond. The FAA inspector interviewed the pilot who stated that the airplane had been refueled with 36 gallons of 100LL fuel from a 55-gallon drum on the morning of the accident. The FAA took samples from the airplane and the drum. The airplane samples were green in color. The samples from the drum were yellow in color. The FAA inspector stated that the drum was equipped with a contamination filter, but he was unable to determine if the inside of the drum was contaminated. The engine was inspected by Safety Board Investigators at Air Transport, an aircraft recovery company, in Phoenix, Arizona, July 14, 1998. Mechanical continuity was established throughout the engine. Crankshaft rotation produced thumb compression in each cylinder, and, accessory gear and valve train continuity was established. The spark plugs were removed for examination. According to the Champion Aviation Spark Plug Check-A-Plug chart, the spark plugs were fouled with lead. Champion writes "lead fouled hard, cinderlike deposits from poor fuel vaporization, high T.E.L. content in fuel or engine operating too cold." The magnetos were rotated and produced sparks at the spark plug leads in proper firing order. The exhaust system was inspected and no obstructions were noted. The oil filter and suction screen were clean. Review of the maintenance records revealed that an annual inspection, which included an oil change, had been completed on June 6, 1998. Approximately 1 hour of flight time had been completed since the annual inspection. The carburetor was inspected and it was noted that there was sewage water in the bowl, and the air bleed jet and main discharge nozzle air orifices were found to be blocked with a white substance. The cylinders were taken off of the engine and the crankcase was separated. According to the Glacier Vandervell, Inc., "How to prevent bearing failures and determine their causes," the number 4 main bearing exhibited evidence of rubbing on the crankshaft and a portion of that bearing insert was severely worn, heat distressed, and had flowed over the edge of the crankcase bearing journal. White metal flakes were found on the bearing insert. The number 6 connecting rod insert exhibited an unidentified white metal substance located in the oil port and its bearing insert was scored and heat discolored. No further discrepancies were noted with the other five connecting rods. The engine was further inspected at Lynn's Aircraft, Mohave Valley, Arizona, on July 21, 1998. A representative from Teledyne Continental Motors, a party to the investigation, assisted in the examination of the engine under the supervision of a Safety Board investigator. According to the representative, the bearings, pistons, and cylinders exhibited heat discoloration. The crankshaft was placed on a crankshaft balance tester, and found to be out of manufacturer's limits. The oil pump was disassembled. It exhibited a nick on one of the driven gear teeth, which corresponded to circumferential scoring on the oil pump housing. Oil galleries were inspected for blockage, and found to be clear. The engine manufacturer representative stated that an overheating of the journal and bearing and " . . . eventual seizure of the shaft in the bearing," resulted from an unidentified white metal traveling through the main oil gallery and being ejected out the number 4 main bearing and cam bore. Metal fragments were found wedged between the number 4 main journal and the corresponding bearing insert and scored the bearing and blocked the clearance between the journal and bearing. According to the carburetor icing probability chart, moderate icing during cruise power conditions existed at the time of the accident.
Oil system contamination with an unidentified metal substance that traveled through the oil system and blocked the number 4 main bearing and number 6 connecting rod bearing oil ports, resulting in oil starvation and failure of the engine. The source of the contamination is undetermined.
Source: NTSB Aviation Accident Database
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