NTSB Final Report: How a Night Medical Flight Ended in a Graveyard Spiral

Five lives were lost after a Pilatus PC-12 entered a steepening descending turn in night IMC near Stagecoach, Nevada.

On February 24, 2023, a Guardian Flight-operated Pilatus PC-12/45 departed Reno-Tahoe International Airport on a non-emergency medical transport to Salt Lake City. The flight was conducted under IFR on a night when winter weather had already affected operations around Reno. Five people were aboard: the pilot, a flight paramedic, a flight nurse, and two passengers. The flight initially followed its departure procedure normally, but about eleven minutes after takeoff its track began to diverge. What followed was a rapidly tightening descending turn that the NTSB found consistent with spatial disorientation and a graveyard spiral.

Accident Facts

The Flight Begins Normally

The crew received an IFR clearance to Salt Lake City and the ZEFFR7 departure via the BLKJK transition. The aircraft departed Runway 17L at about 20:59, climbing through the departure procedure while remaining under ATC control. At 21:08:37, the pilot reported climbing through 15,400 ft to Oakland Center and was cleared to 25,000 ft. The controller also issued a turbulence caution. There was no distress call and no report of a system failure.

The First Signs of Trouble

At about 21:11:15, before reaching the next published waypoint, the aircraft turned right away from the expected route. The aircraft then stopped its previously consistent climb and held about 18,300 ft for roughly 20 seconds despite the clearance to 25,000 ft. It remained on the unexpected heading for about 47 seconds before turning left and continuing northeast. It eventually climbed to about 19,400 ft. The flight path was already abnormal, but the most serious part of the sequence was still ahead.

The Final Turn

At about 21:13:20, the PC-12 entered a descending right turn. Initially the descent rate was about 1,800 ft per minute. Ten seconds later it increased to approximately 13,000 ft per minute, while the rate of turn also increased. ADS-B continued to show the aircraft descending in the tightening turn until contact was lost at about 11,100 ft at 21:14:12. The wreckage distribution was consistent with an in-flight breakup.

What the Investigation Found

Investigators found no mechanical failure that would have prevented normal flight. The engine was producing power at impact, and examination of the autopilot, trim servos and trim actuators found no preimpact failure. The reason for two autopilot disengagements could not be established. The first occurred one to three minutes after takeoff; the second occurred roughly two to four minutes before the accident. After the second disengagement, the pilot had to manually control the aircraft in IMC.

Why the Weather Mattered

The departure environment had already been difficult. Around departure time, Reno reported 1¾ statute miles visibility in light snow and a 1,700-ft ceiling. The NTSB found the aircraft was likely in IMC above 6,000 ft and that icing conditions existed between about 5,000 and 10,000 ft, although there was no evidence of significant structural icing on the accident aircraft. Turbulence was likely present, but the investigation found no evidence of hazardous turbulence causing the loss of control.

The Human and Organizational Evidence

Other air ambulance operators had declined similar flights because of low visibility, snow, wind, turbulence or icing. Care Flight’s procedures required dispatchers to inform crews when another operator had turned down the same patient mission, but investigators found no evidence that the accident crew received that information. The operator also required a flight-risk assessment before every flight, yet no assessment for this flight was found.

A Medical Finding — But Not a Proven Cause

The pilot’s autopsy identified a small right-parietal meningioma. Because that region contributes to the integration of visual and vestibular information, investigators considered whether it might have affected the pilot’s ability to interpret sensory information. The NTSB could not determine whether the tumor contributed, and the pilot’s family had not reported a recent change in health or behavior. The report therefore did not treat the tumor as a proven cause.

What Happened to the Aircraft

The NTSB’s reconstruction fits a classic graveyard-spiral mechanism: in darkness and cloud, the pilot may perceive the aircraft as wings-level while it is actually descending in a turn. Attempts to arrest the descent by pulling back can tighten the turn and increase the descent rate. In this case, the final ADS-B data show exactly the kind of rapidly increasing descent and turn rate associated with that mechanism.

What the Records Show

The NTSB determined that the pilot lost control because of spatial disorientation while operating in night IMC, resulting in an in-flight breakup. The autopilot disengagement for undetermined reasons, insufficient flight-risk assessment and lack of organizational oversight were identified as contributing factors.

Conclusion

N273SM did not disappear because investigators found a single broken component. The final report describes a chain: difficult winter conditions, an inexperienced local operating environment, missing risk information, an unexplained autopilot disengagement, manual control in night IMC and a flight path consistent with a graveyard spiral. The final descent was measurable down to the second, but the reason the pilot could not arrest it was ultimately rooted in spatial disorientation.

Sources & Reconstruction Note

• https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateFinalReport/106784/pdf