What happened
On October 25, 2010, a Mooney M20J, registration N201HF, departed Jackson Hole Airport (JAC) in Wyoming, bound for Pierre, South Dakota. The flight was the first leg of a return trip to Minnesota. The aircraft was occupied by the pilot and his three sons, aged 12, 14, and 14.
Prior to departure, the pilot obtained weather briefings that included AIRMET advisories for mountain obscuration, turbulence, and icing. Although the pilot had originally planned to depart on October 24, weather conditions had delayed the flight. After a commercial flight intended for the return trip was canceled, the pilot elected to fly the Mooney M20J.
Shortly after takeoff, the pilot was issued an air traffic control clearance that differed from his filed flight plan. The clearance included an off-airway segment and an assigned altitude of 14,000 feet, which was lower than the minimum instrument altitude required for that area.
During the flight, the aircraft encountered light turbulence and a trace of rime icing. At approximately 13:51, the pilot reported being in a "severe mountain wave" and stated he was descending rapidly from 13,700 feet. The last radar target was recorded at 13:52 at an altitude of 13,300 feet. The aircraft subsequently disappeared from radar and ground communications.
Search crews located the wreckage in a steep drainage in the Wind River mountain range seven days later. The impact resulted in 4 fatal injuries.
The investigation
Investigators examined the wreckage and found the aircraft was in an upright orientation upon impact, with damage patterns consistent with a left spin. The engine and airframe showed no pre-existing mechanical failures that would have prevented normal operation. The propeller was found to be fractured and scored, consistent with powered rotation at the time of impact.
Radar analysis revealed that the Rock Springs Air Route Surveillance Radar was experiencing reliability issues, and the data had been intentionally made unavailable to controllers at the Salt Lake City Air Route Traffic Control Center. This loss of data meant the aircraft was not eligible for Minimum Safe Altitude Warning (MSAW) protection during a critical period of the flight.
Findings
- The pilot accepted an air traffic control clearance that did not comply with minimum instrument altitude requirements for the area.
- The aircraft was operating near its performance limits in mountainous terrain.
- The pilot encountered severe mountain waves and icing conditions, which likely led to a stall and subsequent spin.
- Air traffic control services were deficient because the controller did not ensure the clearance complied with FAA requirements.
- The decision by the FAA to make certain radar data unavailable prevented the MSAW system from alerting the controller to the hazardous altitude situation.