Accident Sequence
The airplane was in cruise flight when the pilot observed a drop in oil pressure on the cockpit gauge and an intermittent oil warning light. Approximately five minutes later, the engine began to vibrate and subsequently seized with a loud bang. The airplane descended at about 1,000 feet per minute, prompting the pilot to select a dirt field for an emergency landing. During the landing roll, the airplane impacted a berm.
Engine Examination
Post-accident inspection of the engine revealed a concentration of oil on the inside top of the engine cowling, near the firewall on the left side. This location corresponds to the approximate area of the vacuum pump. Removal of the vacuum pump disclosed an oily film on both sides of the pump gasket, which is seated between the vacuum pump flange and the engine accessory case flange.
Vacuum Pump Installation
The vacuum pump had been installed approximately 0.5 flight hours before the accident. The mechanic who performed the installation stated that he used the gasket supplied with the pump. The pump manufacturer reported that they provide a gasket with part number AS3491-01.
Gasket Specifications
The airplane manufacturer's parts manual specifies that the required gasket is part number Z00.N7423254013, which is cross-referenced to Textron Lycoming part number 8313. The investigation was unable to establish a cross-reference or equivalency between the AS3491-01 gasket supplied by the pump manufacturer and either the Lycoming or Socata specified gasket.