What happened
The pilot received a complete weather briefing prior to departing on an IFR flight. The forecast for the intended route included convective thunderstorm activity. At the time of departure, numerous thunderstorms were present in the area, and a tornado watch was active.
After reaching a level of FL210, the pilot reported that conditions were becoming rough. Shortly after this report, the pilot notified air traffic control of problems with the aircraft's gyro system, subsequently stating that all gyros were out. In an effort to locate VFR weather, the pilot elected to descend. During this descent, both radio and radar contact with the aircraft were lost.
The investigation
Wreckage from the accident was located distributed over a path approximately 4-1/2 miles in length. An examination of the wreckage provided evidence that the wings had failed in an upward direction.
Investigators examined the vacuum-powered attitude gyro and found no rotational scratching on the gyro or within its housing. An inspection of the left vacuum pump revealed that the plastic drive coupling showed signs of heat stress and melting; additionally, the internal vanes were broken and cracked, and carbon material deposits were found inside the housing. The right vacuum pump exhibited evidence of rotational scratching. It was noted that the gyros should have remained operational even with only one vacuum pump in service.