Lake Thomas A., CA, USA
N79944
Cessna 172K
The airplane experienced a partial loss of engine power and collided with a tree stump during a precautionary landing on a beach. While climbing through 9,000 feet mean sea level (msl) the pilot leaned the airplane by relying solely on the exhaust gas temperature gauge. When reaching about 9,500 feet msl, about 1,500 feet above ground level over mountainous terrain, the pilot reported that the engine lost partial power. The propeller continued to turn, and the tachometer showed about 2,450 to 2,500 rpm, but the engine failed to produce enough power to sustain level flight. The pilot adjusted the mixture control, while also turning the carburetor heat to the on position, and applying full throttle. The engine failed to respond and the pilot made an approach to a sandy beach. The pilot flared the airplane about 2 feet above ground level, and the left wing collided with a tree stump, veering the airplane to the right. The elevation at the crash site was about 7,600 feet msl. A post accident investigation revealed that the left magneto exhibited excessive play at the cam end (points) of the main shaft. The subject magneto was later functionally tested, which revealed an intermittent spark on ignition lead T1. According to Textron Lycoming Mandatory Service Bulletin 515 the magnetos must be inspected every 500 hours. At the time of the accident, the magneto had accumulated a total time in service of 1,540.23 hours, and there was no maintenance entry indicating that the Service Bulletin had been complied with. While post accident tests showed that the left magneto was working only on an intermittent basis, information provided by Lycoming suggests that in and of itself the complete loss of one magneto would only result in a 3 to 5 percent loss of power. It is likely that the combined effects of the magneto malfunction, the high density altitude, and the pilot's manipulation of the mixture and carburetor heat all played roles in the engine's decreased performance capability.
HISTORY OF FLIGHT On May 24, 2002, about 0645 Pacific daylight time a Cessna 172K, N79944, experienced a partial loss of engine power and collided with tree stumps during a precautionary landing on a beach at Lake Thomas A. Edison, California. Bell Sky Pilots, Inc., was operating the airplane under the provisions of 14 CFR Part 91. The private pilot was seriously injured and the two passengers received minor injuries; the airplane sustained substantial damage. Visual meteorological conditions prevailed, and a flight plan had not been filed. The personal cross-country flight departed Reedley Municipal Airport, Reedley, California about 0620, with a planned fuel stop at Milford Municipal Airport, Milford, Utah, and a planned final destination at Steamboat Springs Airport/Bob Adams Field, Steamboat Springs, Colorado. In a written statement a passenger, who was also the pilot's wife, reported that the flight started out uneventful, with the smooth air and clear weather. While en route, the pilot demonstrated to her how to adjust the mixture control and showed her what the gauges should indicate. The engine began to slow and the pilot adjusted the mixture again, while also turning the carburetor heat to the on position, and applying full throttle. The engine remained at a constant slow sound and the pilot continued to manipulate the mixture control in an effort to regain full power. The airplane began to descend slowly. The needle on the carburetor air temperature gauge was pointing to the left and the pilot continued to leave the carburetor heat on. He still attempted to adjust the mixture control and change fuel tanks, but the engine remained at partial power. As they became in the proximity of Lake Thomas A. Edison, the pilot banked the airplane to the left and they continued to descend. The airplane came to rest in wet sand. The passenger estimated the temperature to be about 40 to 45 degrees Fahrenheit. The National Transportation Safety Board conducted a telephone interview with the pilot about 2 years after the accident. He stated that prior to departure, he verified that both of the fuel tanks were full and then preformed a preflight check. The pilot stated that he used automotive fuel in the airplane, and that the airplane had an STC for use of auto gasoline. After an uneventful departure, he began a climb to his planned cruise altitude of 11,500 feet. While passing through 9,000 feet mean sea level (msl), he leaned the airplane while demonstrating to his wife proper leaning procedures. While climbing through about 9,500 feet msl, with Lake Thomas A. Edison off to the right of the airplane, the pilot reported that the engine lost partial power. With the airplane about 1,500 feet above ground level, the airplane began to descend. The propeller continued to turn, and the tachometer showed about 2,450 to 2,500 rpm, but the engine failed to produce enough power to sustain level flight. He moved the throttle controls, but the engine did not react. He turned the carburetor heat on and began to manipulate the mixture control in an effort to regain power. He noticed a flat sandy beach on the north side of Lake Thomas A. Edison and maneuvered the airplane to land there. The elevation at the crash site was about 7,600 feet msl. He noted the total duration from when the engine lost partial power to the time the airplane collided with tree stumps was about 2 minutes. A fisherman, who witnessed the accident, later reported to the pilot, that about 2 feet above ground level, he saw the airplane flare. The left wing collided with a tree stump and the airplane veered to the right. Several fishermen helped the pilot, his wife, and daughter egress the airplane. The pilot further reported that he and two other pilots owned the airplane together. He stated that the airplane was on a strict maintenance program and, before departing for the trip, the airplane had undergone an annual. The pilot described his leaning procedures as a sole reliance on the exhaust gas temperature gauge when the airplane is at an appropriate altitude. He stated that he manipulates the mixture control until the exhaust gas temperature needle reaches about the 1:00 - 1:30 position on the gauge. The Federal Aviation Administration (FAA) inspector recalled visiting the accident site and examining the airplane after the accident occurred. He stated that he had computed the weight and balance of the airplane to be about 300 to 400 pounds under gross weight. PERSONNEL INFORMATION The pilot was issued a private pilot certificate on May 28, 1985, with a rating for airplane single engine land. The pilot reported a total flight time of 433 hours, with 98 hours in make and model, 5 of which were accumulated in the 90 days prior to the accident. AIRCRAFT INFORMATION All aircraft maintenance logbook records were examined and they revealed that the last documented annual inspection occurred on May 16, 2002, about 3.13 recording tachometer hours before the accident. During the inspection the record indicated that the left magneto had been removed to comply with Airworthiness Directives, at which time the points were set to 25 degrees before top center (BTC). The engine logbook entries indicated that the left magneto, a Bendix S4LN-21, part number 10-51360-37, serial number K088802DR, was installed on May 1, 1989, at a recording tachometer of 55 hours. The magneto had accumulated 1,540.23 hours of service since installation. A review of the logbook entries revealed that both magnetos had been receiving normal routine maintenance through their service life; however, there was no recorded compliance with Textron Lycoming Mandatory Service Bulletin MSB-515 or Teledyne Continental Motors Service Bulletin SB-643 observed in the aircraft maintenance records. TESTS AND RESEARCH At the request of the Safety Board, a Textron Lycoming engine manufacture representative examined the wreckage after recovery at AvParts in Fresno, California, under the supervision of a Fresno Flight Standards District Office aviation safety inspector. According to the engine manufacture representative, the engine did not display any evidence of preimpact catastrophic mechanical malfunction or fire. He removed and examined the bottom spark plugs. He noted that the spark plug electrodes were undamaged from any foreign object ingestion. He rotated the crankshaft by hand utilizing the propeller, and it was free and easy to rotate in both directions. He obtained thumb compression in proper order on all four cylinders. The left magneto was securely clamped in place. The magneto to engine timing was at 28 degrees before top dead center (BTDC) of cylinder number one. The impulse coupling clicked during rotation of the crankshaft. During the magneto-to-engine timing check, the timing was difficult to ascertain due to the fluctuating contact opening intervals obtained during hand rotation of the propeller. Further examination revealed excessive play at the cam end (points) of the main shaft. The drive was intact and properly safetied. A complete copy of the Textron Lycoming report is appended to this report. The left magneto was removed for further examination and sent to a FAA certified repair station for further examination and functional testing. The FAA inspector from Fresno witnessed the procedure. Examination of the left magneto revealed an intermittent spark on ignition lead T1. According to Textron Lycoming Mandatory Service Bulletin 515, dated May 27, 1994, which references Teledyne Continental Motors Service Bulletin 643, dated February 8, 1994, magnetos must be inspected every 500 hours as outlined in the periodic maintenance section of the applicable Service Support Manual, Paragraph 6.2.3. At the time of the accident, the magneto had accumulated a total time in service of 1,540.23 hours, and there was no entry indicating that either Service Bulletin had been complied with. ADDITIONAL INFORMATION In a Textron Lycoming Flyer article, the engine manufacture states that, "Auto fuel is now being used as a substitute for Grade 80 aviation gasoline under STC's issued by the FAA. Most major oil companies and engine manufacturers continue to recommend that aircraft piston engines be operated only on aviation gasoline. Deterioration of engine and fuel system parts have been reported in aircraft using auto fuel. Operators should consider the added risk of using auto fuel in aircraft." A complete copy of the article is appended to this report. The Cessna Pilot Operator Handbook states the following recommended leaning procedure: "pull mixture control out until engine RPM peaks and begins to fall off, then enrich slightly back to peak RPM." The Textron Lycoming operating manual for the engine allows for leaning by various procedures, including the method recommended by Cessna, and also by use of an exhaust temperature gage. Lycoming was quierred on the likely effects on power generation of either the intermittent operation of, or the complete loss of, one magneto. The company representative noted that he was unaware of any study of the matter as such; however, he did note that when performing acceptance tests of new engines in instrumented test cells, the shutoff of one magneto consistently results in the loss of 3 to 5 percent of the power being developed by the engine.
a partial loss of engine power due to the partial malfunction of the left magneto and leakage of the ignition leads for that magneto, due to inadequate maintenance inspections. Factors in the accident include the high density altitude, the maintenance personnel's failure to accomplish a service bulletin, and the effects of the pilot's manipulation of the mixture and carburetor heat controls.
Source: NTSB Aviation Accident Database
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