Piper PA-28-140 N7147R accident near Mosca, Colorado

Probable cause

The pilot's failure to maintain airplane control while attempting to clear a mountain pass in turbulent conditions at a high density altitude, which resulted in the airplane exceeding its critical angle-of-attack and experiencing an aerodynamic stall.

NTSB analysis

The pilot was attempting to fly over a high-altitude mountain pass. Several witnesses reported seeing the airplane flying at a slow groundspeed, about 150 feet above the terrain, through the mountain pass. These witnesses stated that the airplane's engine sounded as if it was operating normally, but the airplane's wings were banking up and down erratically. One of the airplane's passengers reported that the airplane had encountered very turbulent conditions toward the end of the flight and eventually "fell out the sky." The airplane impacted rising terrain near the summit of the 10,040-foot mountain pass in a near vertical impact consistent with an inflight loss of control and subsequent aerodynamic stall. The postaccident investigation did not identify any anomalies that would have prevented normal operation of the airplane.

A postaccident weather simulation indicated that there was a significant potential for turbulence while operating in and downwind of the mountain pass. Additionally, there were several pilot reports of mountain wave action and light-to-moderate turbulence in the mountainous areas surrounding the accident location. Therefore, it is likely that the airplane experienced turbulence while operating within the mountain pass. Additionally, the density altitude was about 12,000 ft, and this would have negatively affected the airplane's climb performance. The combination of the airplane's diminished climb performance and the turbulence made it unlikely that the airplane would be capable of maintaining clearance from the rising terrain, and the pilot likely lost control of the airplane while attempting to do so.

Text from the NTSB. Open the NTSB docket for CEN13FA327 for the full record.