Piper PA-24-250 N7147P accident near Albany, Texas

Probable cause

The loss of flight instrumentation due to a failed vacuum pump while flying a night without a discernable horizon, which resulted in the pilot's spatial disorientation and an in-flight loss of control and impact with terrain. Contributing was the continued operation of the airplane with a recalled and unsafe vacuum pump.

NTSB analysis

After leveling at a cruise altitude of 9,500 feet mean sea level the pilot reported that he had lost instrument suction and his attitude indicator. Radar data showed that the airplane made a climbing right turn and then descended rapidly. Radar and radio contact were lost and the wreckage was found the next morning. Ground and airplane impact signatures showed evidence of a nearly vertical nose down collision with terrain. Other pilots in the area reported a reduction in visibility with blowing dust, which severely restricted visibility and resulted in the loss of a visible horizon. The manufacturer of the vacuum pump had issued a service letter 4 years earlier that indicated that the pump was beyond its mandatory replacement time and must be removed from service. A postaccident examination revealed that the vacuum pump had a preimpact failure that resulted in the loss of all vacuum driven flight instruments.

It is likely that the pilot inadvertently encountered instrument meteorological conditions (IMC) with reduced visibility and the lack of a visible horizon. The airplane's subsequent turning ground track and rapid, near-vertical descent are consistent with the pilot's loss of control of the airplane because of spatial disorientation following the loss of flight instrumentation while flying at night without a discernable horizon.

According to FAA Advisory Circular 60-4A "Pilot's Spatial Disorientation," "Surface references and the natural horizon may at times become obscured, although visibility may be above visual flight rule minimums. Lack of natural horizon or surface reference is common on over-water flights, at night, and especially at night in extremely sparsely populated areas or in low visibility conditions. A sloping cloud formation, an obscured horizon, a dark scene spread with ground lights and stars, and certain geometric patterns of ground lights can provide inaccurate visual information for aligning the aircraft correctly with the actual horizon. The disoriented pilot may place the aircraft in a dangerous attitude."

Text from the NTSB. Open the NTSB docket for CEN12FA164 for the full record.