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On April 23, 1993, at 0815 Pacific daylight time, a Cessna 172N, N6292D, operated by Silverwest Aviation, experienced a total loss of engine power on approach to the Needles Airport, Needles, California. The pilot attempted to glide to Runway 20. The airplane touched down in rough terrain about 200 yards short of the threshold. As the airplane decelerated it nosed over and was substantially damaged. Visual meteorological conditions prevailed at the time of the personal flight, and no flight plan was filed. Neither the private pilot nor the two passengers were injured. The flight originated from Bullhead City, Arizona, on April 23, 1993, at about 0730.
A San Bernardino County Sheriff reported that he interviewed the pilot. The pilot reportedly stated that no mechanical problems were encountered during the en route cruise portion of the flight. Approaching Needles, the airplane's engine began running rough and it started backfiring. Suddenly, all engine power was lost and the engine completely "seized" prior to touchdown.
The airplane was manufactured in 1979 as serial number 17272698. A Lycoming engine, model 0-320-H2AD, serial number L-6338-76, was installed in the airplane along with a single drive (dual) Bendix magneto, part number 10-382555-14K, model D4RN-2021, and serial number 22595. According to Bendix, it manufactured the magneto in 1979.
MAINTENANCE RECORDS EXAMINATION:
The flight school's airplane was recovered from the crash site and was examined. The engine's recording tachometer was observed registering 4,309.2 hours. No evidence was found during the review of the maintenance records that the tachometer had ever been changed.
The records indicated that on July 21, 1984, at an airframe and engine total time of 2,124.8 hours, the engine had received a major overhaul. No evidence was found in the log books indicating the magneto was overhauled. The records further indicated that at the completion of the engine overhaul, the engine (and magneto) were reinstalled on the airframe. The records indicated that the engine and magneto remained in continuous use on the airplane until the accident.
A review of the airplane's recent maintenance revealed that the operator performed an annual inspection on July 28, 1992, at 4,128.3 hours. Also, the operator performed a 100-hour inspection on January 9, 1993, at 4,225.6 hours.
The Safety Board removed the magneto from the engine and examined it. The distributor block was unscrewed from the case, and the bearing stack around the rotating magnet shaft was examined. The bearing stack was found gummy or tacky in feel and almost devoid of lubrication. Resistance was felt upon rolling the bearings. No galling was observed on the rotating magnetic shaft, and no deterioration of the bearings was detected.
The breaker cam was removed and it appeared to have a bluish coloration. (According to Bendix, the cam should normally be black or metallic grey in color.) An accumulation of oil-like material appeared coked onto the cam's roller surface and was found spread circumferentially around the top of the cam near the attachment screw.
The plastic-like cam followers were found worn and had decreased size. They did not open the points upon rotation of the cam.
Evidence was also observed that follower-like material and/or lubricant had tracked and had become deposited circumferentially around the cam's lobes.
The felt oil washers were found dry and in several areas they had a dark, burnt-like appearance. Also, the felt washers were found decreased in size; i.e., portions of the felt were missing.
MANUFACTURER RECOMMENDED MAINTENANCE:
In July of 1992, the FAA published a "General Aviation Airworthiness Alerts" bulletin number 168. In pertinent part, the bulletin addressed aging magnetos and specifically the recommendation by Teledyne Continental Motors for periodic overhauls of its Bendix magnetos in accordance with TCM's Service Bulletin No. 632.
The Bulletin suggested, in part, that the D-2000 series magnetos be overhauled at four-year intervals or at engine overhaul because the magnetos "...use rotating parts and are subject to the same service treatment, environmental conditions and wear as the engine." The Bulletin further indicated that "lubricants will have deteriorated beyond their useful life in magnetos older than four years."
The operator of the flight school reported to the Safety Board during a May 18, 1993, telephone interview that he had rented the accident airplane to the pilot. The operator stated that he possessed an airframe and powerplant mechanic certificate and had inspection authorization. The operator further stated that he was the mechanic who had performed the most recent maintenance on the airplane which included the annual and 100-hour inspections.
The operator stated that he does not routinely receive any accessory part service bulletins or subscribe to a service which provides him with bulletins for magnetos. The only time bulletins are obtained is when they are adopted by regulation into an airworthiness directive.