Pilot’s Somatogravic Illusion & Spatial Disorientation in a Pilatus PC-12 (N933DC) Near Amarillo, TX

On April 28, 2017, a Pilatus PC-12/45 (N933DC) air ambulance, operated by Rico Aviation LLC, crashed shortly after takeoff from Rick Husband Amarillo International Airport, Texas, leading to the deaths of the airline transport pilot and two medical crew members onboard. The aircraft, manufactured in 1994 with 4407 total airframe hours, was en route to Clovis Municipal Airport, New Mexico, in night instrument meteorological conditions. Shortly after departure, air traffic control noticed an incorrect transponder code and abnormal flight patterns, including a rapid ascent to 6,000 feet and erratic changes in pitch and roll angles. After switching frequencies and losing transponder contact, the aircraft rapidly descended at up to 17,000 feet per minute, as per radar data. A surveillance video captured the aircraft's descent at a 45° angle, ending in an explosion. The wreckage was found in a pasture, showing signs of a high-speed, nose-low impact consistent with a loss of control.

The National Transportation Safety Board (NTSB) concluded that the accident was primarily caused by the pilot's spatial disorientation during the initial climb in challenging conditions, including night flying, instrument meteorological conditions, and moderate turbulence. An airplane performance study indicated non-standard maneuvers such as excessive pitch and roll, alongside pilot errors like incorrect transponder setting and unclear communications. These findings, combined with the pilot's limited recent experience in night IFR conditions, suggested he was not fully mentally acute and may have been disoriented. The flight trajectory, and the absence of an aerodynamic stall, pointed to the somatogravic illusion (misleading perception of level flight) playing a role in the crash. The NTSB emphasized the loss of airplane control due to spatial disorientation as the defining event of the accident.

Amelia™

Amelia™ provides Flight Envelope for the aircraft and Health Envelope for the pilot that is an add-on, integrating in a non-intrusive fashion to the avionics. After the accident, an airplane performance study based on radar data and simulations determined that, during the climb to 6,000 ft and about 37 seconds before impact, the airplane achieved a peak pitch angle of about 23°, after which the pitch angle decreased steadily to an estimated -42° at impact. As the pitch angle decreased, the roll angle increased steadily to the left, reaching an estimated -76° at impact. These would not have resulted in an aerodynamic stall but were not in line with expected flight trajectory during or right after the climb.

Pilot ( John F. Kennedy Jr. ) visible from the window with his his wife and sister-in-law in the cabin.

The apparent pitch and roll angles, which represent the attitude a pilot would "feel" the airplane to be in based on his vestibular and kinesthetic perception of the components of the load factor vector in his own body coordinate system, were calculated. The apparent pitch angle ranged from 0° to 15° as the real pitch angle steadily decreased to -42°, and the apparent roll angle ranged from 0° to -4° as the real roll angle increased to -78°. This suggests that even when the airplane was in a steeply banked descent, conditions were present that could have produced a somatogravic illusion of level flight and resulted in spatial disorientation of the pilot. Amelia™ provides a novel 3D holographic interface to the Flight Envelope, an intuitive way to gauge aircraft’s pitch and roll. Even with the somatogravic illusion of level flight, Amelia™ Flight Envelope would have alerted the pilot about the pitch and the roll angle being outside the flight envelope for that phase of the flight. This would have prevented the pilot’s spatial disorientation and the crash that followed.

In addition, analysis of the performance study and the airplane's flight track revealed that the pilot executed several non-standard actions during the departure to include: excessive pitch and roll angles, rapid climb, unexpected level-offs, and non-standard ATC communications. In addition to the non-standard actions, the pilot's limited recent flight experience in night IFR conditions, and moderate turbulence would have been conducive to the onset of spatial disorientation. The pilot's failure to set the correct transponder code before departure, his non-standard departure maneuvering, and his apparent confusion regarding his altitude indicate a mental state not at peak acuity, further increasing the chances of spatial disorientation. Amelia™ Health Envelope may have caught change in pilot’s behavior as a result of not being in peak mental state and alerted the pilot to remain cautious.

Pilot ( John F. Kennedy Jr. ) visible from the window with his his wife and sister-in-law in the cabin.

References

Further read

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