History of Flight
The flight departed runway 31 at Chamberlain Municipal Airport at 1231:58. The airplane lifted off 30 seconds later and immediately entered a left turn. Bank angles initially varied between 10° left wing down to 5° right wing down, then reached a maximum of 64° left wing down at a peak altitude of about 380 ft agl. The airplane then descended until impact. Airspeed during initial climb was between 89 and 97 kts, decaying to about 80 kts as altitude and bank angle peaked. The stall warning and stick shaker activated about one second after liftoff, and the stick pusher activated about 15 seconds after liftoff; all three continued intermittently. A witness about half a mile northwest heard the airplane takeoff in cloudy and snowy conditions but could not see it; he heard the engine "running good" for about 4-5 seconds until the sound stopped. The accident site was discovered at about 1357.
Aircraft Information
The airplane was a Pilatus PC-12/47E, registration N56KJ. It was approved for day/night operations under VFR and IFR, including flight into known icing conditions. It had two flight crew seats and eight passenger seats (total ten), but twelve individuals were on board, none qualifying as lap children. Estimated weight and balance showed the airplane was about 107 lbs over maximum gross weight, and the center of gravity was 3.99 to 5.49 inches beyond the aft CG limit. The airplane was stable on the ramp due to main landing gear location; if CG had been aft of the pivot point, the tail would have tipped back. Photos and video showed accumulated snow on the horizontal and vertical stabilizers, with icicles on the horizontal stabilizer bullet fairing, while parked and during taxi. The airplane flight manual specified a takeoff rotation speed of 92 kts at maximum gross weight in icing conditions.
Meteorological Information
Winter weather had persisted for 12 to 24 hours. Light to moderate snow, freezing drizzle, and mist occurred throughout the night and morning, with 2.1 inches of snow accumulation from 0730 the previous day to 0730 on the accident day. Surface observations indicated low IFR conditions at the time; moderate snow was observed at 1235. Atmospheric soundings indicated moderate or greater airframe icing conditions were likely from the surface to 11,500 ft. AIRMET advisories for moderate turbulence, moderate icing, and IFR conditions were in effect at the time. The pilot obtained a weather briefing at 1204, which included METARs, PIREPs, and TAFs, but did not request current AIRMETs. The airport manager reported plowing snow from about 0830, estimating up to 2 inches had fallen over 24-36 hours, and felt the weather was deteriorating.
Wreckage and Impact Information
The accident site was about 3/4 mile west of the airport in a dormant corn field. The debris path was about 85 ft long, oriented on a 179° heading. The engine separated from the firewall, and the left wing separated at the root; both were in the debris path. The main wreckage comprised the fuselage, right wing, and empennage. Postaccident examination revealed no preimpact failures. The flaps were set at 15° and landing gear retracted. Trim was within takeoff range. LDR data showed engine parameters consistent with rated takeoff power, with no anomalies.
Medical and Pathological Information
Toxicology testing found no drugs of abuse.
Additional Information
A performance study using desktop and piloted simulations indicated that flight control authority was sufficient until an aerodynamic stall about 22 seconds after liftoff. The maximum bank angle of 64° occurred after critical angle-of-attack was exceeded. Simulations did not show significant performance degradation from residual snow and ice on the empennage, though effects on CG and airflow over the horizontal stabilizer are unknown. The previous day's flight from Idaho Falls to Chamberlain had similar loading. LDR data from that takeoff showed a rotation pitch rate of about 4.3°/sec, pitch angle above the 9° flight director target, and pitch oscillations possibly due to decreased stability. The accident pilot's rotation technique involved a relatively abrupt pull, initiated at about 88 kts (4 kts slower than specified), with an initial pitch angle of 11.8° pausing briefly before continuing to 15.8°. In contrast, another pilot flying the same airplane used rotation rates of 3°/sec and lower initial pitch angles. Simulator participants found takeoff easier to control with lower pitch rates and angles.