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 article revisits a Pilatus PC-12 crash, correcting an initial misinterpretation and confirming the aircraft broke apart mid-flight after entering an uncontrolled spiral dive from autopilot disconnect in IMC, with no apparent pilot intervention.
Piloted aircraft are inherently prone to spiral divergence if left uncontrolled, leading to dangerous speed and bank increases.
A key takeaway is that recovery from a high-speed spiral dive, especially if the aircraft was initially trimmed for low speed, can generate dangerously high G-forces (even without pilot input to pitch up) that exceed structural limits and cause in-flight breakup.
Effective recovery requires specific actions to limit G-forces, such as powering off, leveling wings, trimming nose-down, pushing forward on the yoke, and potentially deploying landing gear to increase drag and reduce speed safely.

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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.