WPR18FA139 · Beech 76

During the 2-hour nighttime visual flight rules instructional cross-country flight, radar data identified the airplane on an easterly flight track when the first of two maneuvers over mountainous terrain was initiated. The first maneuver was a left turn from about a 48° course heading to about a 176° course heading. Throughout the turn, the airplane's altitude remained about 5,600 ft mean sea level (msl), and the groundspeed decreased to 55 knots. At the completion of the turn, the groundspeed increased to about 67 knots, and the airplane began to climb to 6,600 ft msl while continuing to the southwest on a course heading of about 195°. The airplane then made a right turn course reversal and resumed the easterly heading for about 10 miles.

The radar data then depicted the airplane initiated a second left 180° turn maneuver at an altitude of 6,200 ft msl and a groundspeed of about 121 knots. At the apparent apex of the turn, the airplane was at 6,100 ft msl and a groundspeed of 50 knots. The airplane then began to descend, and the groundspeed increased to 74 knots and then decreased to 50 knots. The last radar return showed the airplane at an altitude of 5,700 ft msl and a groundspeed of 67 knots near the accident site. Radar data revealed that both maneuvers were similar except that the second maneuver began over higher elevation terrain. The airplane's separation from the terrain during the second maneuver was as low as 1,200 ft above ground level (when the airplane was at an altitude of 6,100 ft and was over terrain that was 4,900 ft) before radar contact was lost.

Weather reporting in the aera of the accident site indicated extreme turbulence and severe up and downdrafts during high wind conditions. Although there is evidence of strong wind in the area at the time of the second maneuver, there is no consensus among the available wind data. However, the upset occurred immediately downwind of relatively high terrain and inside of a temperature inversion, which can promote wave action and turbulence. Thus, the airplane likely encountered a downdraft and the pilot was unable to recover, resulting in the airplane's subsequent impact with terrain.

The operator reported that the instructor was newly hired to the flight school and that the accident flight was his first instructional flight with the company. The course syllabus for the flight identified that several tasks were to be accomplished. A representative of the operator reported that maneuvers were usually performed to facilitate a 2-hour flight. All flight was prohibited below 500 ft agl and minimum cruise altitude of 2,000 ft agl in mountainous terrain. No flight plan had been filed for the nighttime flight, and any en route flight planning documentation was destroyed in the postimpact fire; thus it could not be determined if the pilot or the flight instructor were aware of the weather conditions or terrain elevations while performing the maneuvers.

Verbatim NTSB analysis and probable cause from the NTSB dataset