Icing Encounter and Loss of Control

By Richard N. Aarons
Source: Business & Commercial Aviation

The outboard section of the right wing and several sections of the empennage, including the horizontal stabilizer, elevator and rudder, were found about 1,200 ft. southwest of the fuselage in a residential area.

Investigators performed a visual inspection of the pneumatic leading edge deice boots and uncovered no preexisting ruptures or cracks. All observable boot fasteners were intact and secure. Impact damage prevented functional testing of the aircraft deice systems. The cockpit deice system panel was found intact.

The airframe deice, propeller deice, pilot heat 1 and 2, and stall warning heater switches were found in the “ON” positions. The ice inspection light, the left and right windshield deice, and the inertial separator switches were found in the “OFF” positions.

Examination of the carry-through structure, where the wings were attached to the fuselage, exhibited twisting and bending distortion at the right wing attachment points in the up and aft direction. The carry-through structure was fragmented. All fracture surfaces exhibited overload signatures. No evidence of preexisting cracks or fatigue was observed.

Examination of the outboard section of the right wing determined that the wingtip, aileron and spoiler remained attached. Examination of the aileron attachment and actuator hardware revealed no evidence of stop-to-stop damage.

During the examination of the airframe structure, the outboard section of the right wing was manually positioned, or “mated,” with the leading edge of the right-hand horizontal stabilizer to explore the possibility of inflight contact. The examination revealed that deformation on the leading edge of the right wing was consistent with an inflight contact with the leading edge of the right-hand horizontal stabilizer. Also, impact signatures and damage observed on the right wing leading edge were consistent with an inflight collision with the right side of the rudder.

The engine displayed contact signatures at the compressor first stage and shroud, compressor turbine, compressor turbine shroud, first-stage power turbine vane ring, first-stage power turbine, first-stage power turbine shroud, second-stage power turbine vane ring, second-stage power turbine and second-stage power turbine shroud. The engine housing exhibited severe radial deformation around the right-hand circumference, resulting in circumferential impact fractures of the compressor turbine blades and the first- and second-stage power turbine blades.

The examination of the propeller revealed that three of the propeller blades remained attached to the propeller hub and a fourth blade separated into two sections. The blades exhibited twisting, chord-wise scratching, “s” bending and blade-tip separations.

In short, said the investigators, the examination of the airframe and engine revealed no evidence of a pre-accident mechanical malfunction or anomaly.

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