NTSB Report On PC-12 In-flight Breakup

Spatial disorientation following autopilot disengagement led to the in-flight breakup of an air ambulance Pilatus PC-12 near Stagecoach, Nevada, on Feb. 24, 2023, according to the NTSB’s final report. The pilot, flight nurse, flight paramedic, and two passengers were killed.

The PC-12, N273SM, was operated by Guardian Flight under the Care Flight brand. At 9:00 p.m. local time, the non-emergency medical transport departed Reno-Tahoe International Airport (KRNO) under an IFR clearance in night instrument meteorological conditions (IMC), with cloud bases at 1,200 feet agl and tops at FL240. According to the report, the pilot was cleared to climb to 25,000 feet but did not reach that altitude.

About 11 minutes into the flight, the aircraft veered from its assigned route and began a series of altitude and heading changes. The NTSB concluded that the flight profile was consistent with a graveyard spiral, a form of spatial disorientation where the pilot misperceives a descending turn as level flight and, adding backpressure to the yoke to compensate for a perceived level descent, tightens the spiral until the aircraft crashes or loses structural integrity due to forces of flight.

“The pilot’s loss of control due to spatial disorientation while operating in night instrument meteorological conditions…resulted in an in-flight breakup,” the NTSB found. Contributing factors included “the disengagement of the autopilot for undetermined reasons, as well as the operator’s insufficient flight risk assessment process and lack of organizational oversight.”

Twice during the brief flight, the PC-12’s autopilot disengaged. The second disengagement occurred about two to four minutes before the accident. The autopilot was not reengaged, requiring the pilot to manually control the aircraft in IMC. No mechanical anomalies were found with the autopilot, trim servos, or other control systems.

After the aircraft climbed to approximately 19,400 feet msl, it entered a steep descending right turn. The descent rate increased to more than 13,000 fpm before radar contact was lost near 11,100 feet msl. The distribution of wreckage and structural fractures was consistent with an in-flight breakup caused by aerodynamic overstress.

The pilot was classified as a “float” pilot assigned to various bases, including Reno. He had been hired only five months prior, the NTSB noted, and had limited recent experience in the aircraft and operating area. Neither of the two medical personnel on board had been with the company for more than six months, and they had been paired just 14 days prior to the accident.

No risk assessment for the accident flight was found, and the operator’s fixed-wing division lacked the crew pairing requirements applied to its rotorcraft operations. Although other operators had declined similar flights earlier in the day due to weather, the accident crew was not informed of this.

An autopsy of the pilot revealed a three-centimeter brain tumor in the right parietal lobe—an area responsible for integrating sensory and navigational input. While the NTSB could not determine whether the tumor contributed to the accident, it acknowledged that the condition “may have impacted the pilot’s ability to synthesize and respond to sensory interpretation.”

The aircraft was not equipped with cockpit voice or flight data recorders, but onboard systems and GPS data allowed investigators to reconstruct the flight path. No mechanical failures were found that would have precluded normal operation.