What happened
Shortly after reaching cruise altitude, the pilot observed a loss of oil pressure on the cockpit gauges accompanied by an intermittently flickering oil warning light. Approximately five minutes later, the engine began to vibrate and subsequently seized following a loud bang. The aircraft entered a descent of approximately 1,000 feet per minute. The pilot attempted an emergency landing in a dirt field, but during the landing roll, the Socata TB-20 collided with a berm. There were no fatalities reported.
The investigation
An examination of the engine revealed a concentration of oil on the inside top of the engine cowling near the firewall on the left side, specifically near the location of the vacuum pump. Upon removal of the vacuum pump, an oily film was discovered on both sides of the pump gasket, which is seated between the vacuum pump flange and the engine accessory case flange. The vacuum pump had been installed approximately 0.5 hours before the accident. The mechanic responsible for the installation stated that the gasket supplied with the pump was used. While the vacuum pump manufacturer provides part number AS3491-01, the aircraft manufacturer's parts manual specifies part number Z00.N7423254013 (cross-referenced with Textron Lycoming part number 8313). The investigation could not establish an equivalency between the gasket supplied by the pump manufacturer and the required Lycoming or Socata specifications.
Findings
- The engine failure was caused by oil exhaustion.
- An improper gasket installation or use of an incompatible gasket led to oil leakage from the vacuum pump area.