Cessna 172R N9417Z accident near Jackson, Tennessee

Probable cause

A total loss of engine power due to maintenance personnel’s improper installation of the lower vacuum pump.

NTSB analysis

The pilot reported that, during the climb after takeoff in instrument meteorological conditions, he noted that the engine was losing oil pressure rapidly. He immediately made a 180-degree turn to return to the departure airport. While inbound on the instrument landing system (ILS) approach, he realized that the airplane was too high, so he executed a 360-degree descending turn. He then again proceeded inbound on the ILS approach. He continued the descent but, because the airplane had not captured the glideslope, he executed a missed approach. He then circled the airplane around and re-established the airplane on the localizer. Subsequently, the engine lost all power, and the airplane began descending. The pilot subsequently landed the airplane on a road just north of the airport. During the landing, the right wing impacted a highway sign, which resulted in substantial damage to the right wing. The airplane then veered right and entered a cornfield.

Examination of the wreckage revealed the presence of oil on the back of the engine, firewall, and belly. The engine was started with the engine cowling removed, and oil was observed to appear on the back of the accessory pad near the lower vacuum pump. Further examination of the area revealed that the accessory drive adapter gasket was the source of the leak. Review of the airplane's maintenance records revealed that, on the day before the accident, the lower vacuum pump had been removed and that a new vacuum pump, shaft seal, and accessory drive adapter gasket had been installed. Examination revealed that the proper gasket was installed; however, it was distorted and showed signs of excessive compression and "squeezeout," which indicated that the nuts had been overtorqued during installation.

Text from the NTSB. Open the NTSB docket for ERA14LA142 for the full record.