Revisiting the PC-12 Crash

Peter Garrison

Monday, August 24, 2015 at 10:55 PM ET

Verified

** The PC-12, with six aboard, had barely begun its trip
when the pilot lost control of the airplane.**

Key Takeaways:

The 2012 Pilatus PC-12 crash exemplifies the catastrophic outcome of pilot inaction following an autopilot disconnect in IMC, leading to an uncontrolled spiral dive and subsequent in-flight breakup due to structural overstress.
Aircraft inherently exhibit "spiral divergence," meaning they will enter an increasingly steep spiral dive if left uncontrolled, a risk significantly heightened for pilots who lose visual references in IMC.
Recovery from a high-speed spiral dive, especially if the aircraft was initially trimmed for a much slower speed, can induce dangerously high G-forces that exceed the airframe's ultimate load factor, causing structural failure.
To prevent in-flight breakup during recovery from an extreme spiral dive, pilots must prioritize limiting G-forces by trimming nose-down and pushing the yoke forward after leveling the wings, and using drag devices to reduce speed without further overstressing the aircraft.

See a mistake? Contact us.

In my March Aftermath column on the 2012 crash of a Pilatus PC-12 in Florida, I faulted the National Transportation Safety Board for mixing up indicated and true airspeeds. Actually, it was I who misread the report. I am indebted to reader Timothy Burtch, an accident investigator with the NTSB, for pointing out that the maximum speed of 338 knots that the airplane reached in a spiral dive before it broke apart was, in fact, an indicated airspeed, not a true one, and that the airplane did, therefore, exceed its maneuvering speed by
175 knots as the report stated.

The Pilatus, with a family of six aboard, was climbing through FL 250 in IMC. It was at 109 kias, in a 25-degree right bank, deviating to avoid an area of rain, when the autopilot disengaged for unknown reasons. Presumably a chime sounded and a warning light illuminated, but the pilot seemingly did nothing to take control of the airplane. The baffling aspect of that accident was the pilot’s apparent failure to act even when the airplane was vertically banked and plunging downward at a horrific rate.