What happened
On April 28, 2017, a Pilatus PC-12 operating as an air ambulance crashed near Rick Husband Amarillo International Airport (AMA) in Amarillo, Texas. The flight was an instrument flight rules (IFR) mission intended to transport a patient from Clovis, New Mexico, to Lubbock, Texas.
Shortly after departing runway 4, the local air traffic controller observed the N933DC displaying an incorrect transponder code while climbing through 4,400 feet MSL. After the pilot was instructed to reset the code, the aircraft leveled off briefly before resuming a climb to 6,000 feet MSL. At 23:46:54, the pilot contacted departure control to report being at 6,000 feet. However, approximately one minute later, the departure controller reported that the aircraft's transponder signal was lost. The pilot did not respond to subsequent radio calls.
Radar data and an aircraft performance study indicated the airplane entered a rapid descent, reaching a rate of 17,000 feet per minute. Surveillance video from a nearby location captured the aircraft's lights descending at a 45-degree angle, followed by an explosion. The aircraft impacted a pasture approximately 1.5 nautical miles south of the airport, resulting in 3 fatal injuries.
The investigation
Investigators examined the wreckage and found the airplane was heavily fragmented. The engine and propeller showed evidence of operation during the impact. A performance study using radar data and simulations determined that the aircraft's pitch angle reached a peak of 23 degrees before steadily decreasing to an estimated -42 degrees at impact. Simultaneously, the roll angle increased to an estimated -76 degrees. The study concluded the aircraft was not in an aerodynamic stall.
Analysis of the autopilot system revealed that the "autopilot disengage" caution indicator was likely illuminated at the time of impact. Testing on an exemplar aircraft suggested the pilot may have engaged the autopilot only seconds before it automatically disconnected due to exceeding the +1.6g load factor limit. The investigation also noted that the operator had previously reported unexpected autopilot disconnects, and a video from two days prior showed the autopilot disconnecting during flight.
Findings
- The pilot's flight path included non-standard maneuvers, such as excessive pitch and roll angles, rapid climbs, and unexpected level-offs.
- The pilot's recent flight experience in night IFR conditions was limited.
- The presence of moderate turbulence and night instrument meteorological conditions created conditions conducive to spatial disorientation.
- The pilot's failure to use the correct transponder code and confusion regarding altitude suggested a mental state that was not at peak acuity.
- The aircraft's apparent pitch and roll angles during the descent could have produced a somatogravic illusion, leading the pilot to believe the airplane was in level flight while it was actually in a steep descent.