Mooney M20K N231EC accident near Baker City, Oregon

Probable cause

The pilot's exceedance of the airplane's critical angle of attack during the landing approach as a result of his diversion of attention after a series of non-essential aircraft systems became inoperative following the failure of the engine-driven vacuum pump, which resulted in an aerodynamic stall/spin.

NTSB analysis

The pilot and student pilot-rated passenger were in a high-performance airplane and inbound for landing. Multiple witnesses saw the airplane on the downwind leg of the airport traffic pattern; one witness estimated that the airplane was lower and closer to the runway than a typical traffic pattern. Witnesses then saw the airplane begin a left turn, and one reported that the airplane then rapidly transitioned to a nose-down descent.

The wreckage location corresponded to an extended downwind-to-base turn; there was ample space available for the pilot to initiate the turn to final without excessive flight control inputs. The airplane appeared to be in the landing configuration, and debris distribution and damage indicated a near vertical, nose-down impact, consistent with the airplane impacting the ground while in a spin.

Postaccident examination did not reveal any anomalies with the airframe or engine that would have precluded normal operation, and the engine appeared to be operating at the time of impact; however, evidence suggested that the airplane's engine-driven vacuum pump had recently failed. Such a failure would have resulted in multiple visual alerts, caused the vacuum-operated instruments to become inoperative, and prevented operation of the airplane's speed brakes. The airplane was equipped with a backup vacuum system; however, impact damage prevented an accurate assessment of its operational status at the time of the accident. The vacuum pump had exceeded its manufacturer's recommended replacement life and had been subjected to multiple sudden engine stoppage events, each of which required replacement of the pump; however, there was no indication in the airplane's logbooks that the pump had been replaced following these events.

Although none of the systems that relied on the vacuum pump were critical for visual flight rules operation, such a failure would have presented an operational distraction to the pilot that would have competed for his attention while flying in the pattern. Based on witness reports and the location of the wreckage, it is possible that he extended the downwind leg to attempt to manage the failure or in an effort to slow the airplane further in order to land without the speed brakes.

The presence of a systems failure may have exceeded the pilot's capability to appropriately divide his attention between airplane control and systems management. The pilot had relatively low flight experience and had demonstrated poor situational awareness and pilot resource management during his initial private pilot practical test, which he failed on the first attempt. He was also involved in a hard landing with the accident airplane about 2 months before the accident, resulting in damage to the propeller and landing gear. His flight instructor expressed concern that the complex, high-performance airplane was too fast and advanced for the pilot's level of experience. He recounted how the pilot often struggled with maintaining a stabilized landing approach and often allowed the airplane to "get ahead of him."

It is likely that the pilot became distracted during the landing approach and allowed the airplane to slow down and exceed its critical angle of attack during the turn from the downwind to base leg, resulting in an aerodynamic stall and spin at an altitude too low for recovery.

Text from the NTSB. Open the NTSB docket for WPR18FA218 for the full record.