Mathis Field Airport
Aircraft Accident/Incident Report

San Angelo, Texas 76901
Monday, November 16, 1998 18:45 CST

The airplane was en route cruising at 9,500 feet msl approximately 12 miles east of its destination, when the pilot reported a loss of engine power. At 2,200 feet msl, the pilot reported that he would not make the runway. During the off airport landing, the airplane struck a tree, the right wing separated from the airframe, the airplane descended into the water, and came to rest inverted in water 7 feet deep. Examination of the wreckage revealed engine oil in the single drive dual magneto and one of the rear case bearing retaining plate screws was broken. The magneto was removed from the engine and disassembled. A metallurgist found that screw failure was a result of delayed fracture from hydrogen embrittlement and the 'hydrogen was most likely picked up during the cadmium plating for corrosion resistance at original manufacture of the screw.' The magneto had accumulated 775.58 hours since last overhaul in 1993. At the last annual inspection, November 1998, the magneto points and timing were checked. Time since that annual inspection was 3.27 hours. Service Bulletin (SB) 643 dated 02/08/94 recommended magnetos be 'overhauled or replaced at the expiration of four years without regard to the accumulated operating hours since new or last overhaul.' No evidence was found that the SB had been accomplished; however, under 14 CFR Part 91 operations, compliance with the SB is not required.

The total loss of engine power due to the magneto failure resulting from oil contamination when the bearing plate retainer screw fractured due to improper manufacturing. Factors were the lack of suitable terrain for the forced landing, and the dark night conditions.