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Aviation Accident

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NTSB Identification: ERA12FA385
14 CFR Part 91: General Aviation
Accident occurred Thursday, June 07, 2012 in Lake Wales, FL
Probable Cause Approval Date: 11/24/2014
Aircraft: PILATUS AIRCRAFT LTD PC-12/47, registration: N950KA
Injuries: 6 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The instrument-rated pilot activated the autopilot shortly after takeoff and proceeded in a west-northwesterly direction while climbing to the assigned altitude of flight level (FL) 260. Light-to-moderate icing conditions were forecast for the area; the forecast conditions were well within the airplane's capability, and the pilot of a nearby airplane reported only encountering light rime ice at the top of FL260. About 26 minutes 35 seconds after takeoff, the airplane's central advisory and warning system (CAWS) recorded activation of Pusher Ice Mode at FL247, consistent with pilot's activation of the propeller de-ice and inertial separator; the de-ice boots were not selected. Less than a minute after the activation of Pusher Ice Mode, an air traffic controller cleared the flight to deviate right of course due to adverse weather well ahead of the airplane. The airplane then turned right while on autopilot in instrument meteorological conditions (IMC) at FL251; about 4 seconds into the turn, with the airplane indicating about 109 knots indicated airspeed and in a right bank of less than 25 degrees, the autopilot disconnected for undetermined reasons. The pilot allowed the bank angle to increase, and about 13 seconds after the autopilot disconnected, and with the airplane descending in a right bank of about 50 degrees, the pilot began a test of the autopilot system, which subsequently passed. Recovered data and subsequent analysis indicate that the pilot allowed the bank angle to increase to a minimum of 75 degrees while descending; the maximum airspeed reached 338 knots. During the right descending turn, while about 15,511 feet and 338 knots (about 175 knots above maximum operating maneuvering speed), the pilot likely applied either abrupt or full aft elevator control input, resulting in overstress fracture of both wings in a positive direction. The separated section of right wing impacted and breached the fuselage, causing one passenger to be ejected from the airplane. Following the in-flight break-up, the airplane descended uncontrolled into an open field.

Examination of the separated structural components revealed no evidence of pre-existing cracks on any of the fracture surfaces. Postaccident examination of the primary flight controls and engine revealed no evidence of preimpact failure or malfunction. The flaps were found in the retracted position, and the landing gear was extended; it is likely that the pilot extended the landing gear during the descent. The horizontal stabilizer trim actuator was positioned in the green arc takeoff range, the impact-damaged aileron trim actuator was in the left-wing-nearly-full-down position, and the rudder trim actuator was full nose right. The as-found positions of the aileron, rudder trim, and landing gear were not the expected positions for cruise climb. Examination of the relays, trim switch, and rudder trim circuit revealed no evidence of preimpact failure or malfunction, and examination of the aileron trim relays and aileron trim circuit revealed no evidence of preimpact failure or malfunction; therefore, the reason for the as-found positions of the rudder and aileron trim could not be determined. Impact-related discrepancies with the autopilot flight computer precluded functional testing. The trim adapter passed all acceptance tests with the exception of the aural alert output, which would not have affected its proper operation. The CAWS log entries indicated no airframe or engine systems warnings or cautions before the airplane departed from controlled flight. A radar performance study indicated that the airplane did not enter an aerodynamic stall, and according to the CAWS log entries, there was no record that the stick pusher activated before the departure from controlled flight.

Before purchasing the airplane about 5 weeks earlier, the pilot had not logged any time as pilot-in-command in a turbopropeller-equipped airplane and had not logged any actual instrument flight time in the previous 7 years 4 months. Additionally, his last logged simulated instrument before he purchased the airplane occurred 4 years 7 months earlier. Subsequent to the airplane purchase, he attended ground and simulator-based training that included extra flight sessions in the accident airplane, likely due to his inexperience. The training culminated with the pilot receiving his instrument proficiency check, flight review, and high-altitude endorsements; after the training, he subsequently logged about 14 hours as pilot-in-command of the accident airplane. Although the pilot likely met the minimum qualification standards to act as pilot-in-command by federal aviation regulations, his lack of experience in the make and model airplane was evidenced by the fact that he did not maintain control of the airplane after the autopilot disengaged. The airplane was operating in instrument conditions, but there was only light rime ice reported and no convective activity nearby; the pilot should have been able to control the airplane after the autopilot disengaged in such conditions. Further, his lack of experience was evident in his test of the autopilot system immediately following the airplane's departure from controlled flight rather than rolling the airplane to a wings-level position, regaining altitude; only after establishing coordinated flight should he have attempted to test the autopilot system.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
  • The failure of the pilot to maintain control of the airplane while climbing to cruise altitude in instrument meteorological conditions (IMC) following disconnect of the autopilot. The reason for the autopilot disconnect could not be determined during postaccident testing. Contributing to the accident was the pilot's lack of experience in high-performance, turbo-propeller airplanes and in IMC.