Accident Sequence
Approximately five minutes after departure, the pilot observed the oil low pressure warning light illuminate. Shortly thereafter, a knocking sound was heard from the engine. The pilot initiated an engine shutdown and attempted to return to the departure airport. Unable to reach the runway, the pilot executed a power-off landing to a rough open field located about one mile from the airport.
Landing and Damage
The touchdown was uneventful; however, during the landing roll, the aircraft encountered a ditch. This resulted in the separation of the nose gear and substantial damage to the aircraft structure.
Post-Accident Inspection
On-site examination of the aircraft revealed oil residue at the aft end of the engine near the accessory section. After the tail was lowered, a notable oil leak was observed at the vacuum pump flange, with a flow rate of approximately six drops per minute. Further inspection of the engine found that the pneumatic pump gasket had failed and was displaced upward from between the mating surfaces of the pump and its mounting pad.
All four mounting nuts of the pneumatic pump were found to be only slightly tighter than finger tight and could be removed without resistance. The internal star locking washers were in place under the nuts and showed signs of crushing, indicating that proper torque had been applied at some point. Standard torque for these nuts is 90 inch-pounds.
Probable Cause
No probable cause was stated in the source material.