GRAYLING, AK, USA
N9704N
Maule M-5-210C
The certificated private pilot departed a remote airstrip. About 1,000 feet above the ground, the engine quit. The pilot performed an emergency landing on soft snow covered terrain and the airplane nosed over. An engine examination revealed that the alternator drive coupling, consisting of a hub, retainer and bushing, fragmented within the engine. The alternator drive shaft and the oil pump gear were fractured when fragments of the retainer were enmeshed in the engine accessory gear teeth that drove both accessories. The number 6 cylinder connecting rod failed and penetrated the engine case due to a lack of lubrication. The engine, including the alternator, was overhauled 250 hours before the accident. An engine manufacturer's service bulletin recommended inspection and replacement of the standard alternator drive coupling every 500 hours. The engine manufacturer offered a one piece alternator drive coupling in which the retainer, bushing and hub were bonded together as one unit.
On April 20, 1996, about 1700 Alaska daylight time, a wheel equipped Maule M-5-210C, N9704N, crashed during a forced landing about 6 miles north of Grayling, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight when the accident occurred. The airplane, registered to and operated by the pilot, was destroyed. The certificated private pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed. The flight originated at the Grayling airport about 1650. The pilot reported that after departure, he climbed to about 1,000 feet above the ground. The engine suddenly began losing power and producing smoke and then quit running. The pilot performed an emergency landing on soft snow covered terrain and the airplane nosed over. After the airplane was recovered, an examination of the engine revealed that the number 6 cylinder connecting rod had penetrated the engine case. The engine, a Continental IO-360-D33A, serial number 351098, was overhauled on October 1, 1993, by Nix Flying Service, Hamilton, Alabama. At that time the engine had accrued 1,609 hours of operation. The overhaul endorsement contained in the engine logbook indicated that the magnetos, fuel pump, starter, and alternator were also overhauled. The maintenance records did not contain any yellow serviceable tags for the overhauled components. The engine then accrued an additional 250 hours before the accident. The most recent annual inspection was accomplished in May, 1995, 200 flight hours before the accident. On May 1, 1996, an engine examination was conducted at B J Engines, Palmer, Alaska. The parties noted in this report participated in the examination. The number 6 cylinder connecting rod was protruding through the top of the crankcase. The paint was blistered above the bases of the number 5 and 6 cylinders. The crankcase halves were separated and examined. Both halves exhibited impact damage from the number 6 connecting rod which had broken at the rod bolts and cap. The number 5 cylinder intake valve lifter and crankcase bore were broken away from the crankcase. Little lubrication was present in the rod bearings. The alternator was removed from the accessory end of the engine. The shaft was fractured at the rear face of the drive shaft retaining nut. One half of the alternator drive hub was fractured and was lying in the oil sump. The alternator drive retainer and bushings (coupling) were also missing with fragments of each located in the engine oil sump. Fragments of the retainer were also found wedged into the accessory gear teeth that mate with the alternator drive gear and the oil pump drive gear. The oil pump drive gear is driven by the same accessory gear that drives the alternator. The engine oil pump shaft was fractured immediately behind the drive gear and was located in the accessory gear recess. The engine alternator is the subject of Teledyne Continental Motors Service Bulletin SB95-3A, issued May 10, 1995, and revised on December 15, 1995. It was issued following reports of coupling assemblies that were severely worn or damaged. The service bulletin recommends that alternator drive couplings with more than 500 hours total time in service, be inspected within the next 25 hours of operation and every 500 hours thereafter. The service bulletin is not mandatory. The standard alternator drive coupling consists of a metal retainer into which rubber bushings are inserted to absorb vibration. The retainer is positioned in a "U" shaped hub. A one piece drive coupling is available in which the retainer, bushing, and hub are bonded together as one unit. If the drive coupling is a standard coupling, the service bulletin requires replacement of the coupling retainer and bushings and proper torquing of the drive gear nut. If the drive coupling is a one piece design, the retainer and bushings are a single unit and the service bulletin only requires an inspection and proper torquing of the drive gear nut. The Safety Board released the engine to the owner on May 1, 1996. No parts or components were retained by the Safety Board.
disintegration of the alternator drive coupling, jamming of the accessory drive gear, shearing of the oil pump drive, oil starvation, and failure of the number 6 cylinder connecting rod. Non-compliance with a manufacturer's service bulletin and soft snow were factors in the accident.
Source: NTSB Aviation Accident Database
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