What happened
A private pilot was conducting an IFR flight back to his home base at night under IMC conditions. Several minutes before the accident, the pilot notified Air Traffic Control (ATC) that his instrument gyro had failed. Although he later reported that his instruments were still functioning, he noted a warning light was illuminated and stated he was "in trouble." ATC observed the aircraft entering a rapid descent, after which radar contact was lost. The aircraft subsequently impacted wooded terrain in a steep, nose-low attitude.
The investigation
An examination of the aircraft's vacuum system determined that the engine-driven vacuum pump had failed due to oil ingestion. Investigators found that an engine oil leak had been repaired in June 1993. This leak originated at the engine accessory drive seal, which serves as the attachment point for the vacuum pump on the engine. The investigation further revealed that the failed pump had been installed as a new unit approximately one week prior to the repair of the oil leak. Notably, the previous vacuum pump, which was removed during the June 1993 repair, had also failed due to oil ingestion.