History of the Flight
The pilot prepared for a cross-country flight from Lille-Lesquin to Aix-les-Milles under an IFR flight plan. After takeoff at 12:02, the pilot climbed to FL 110 and engaged the autopilot. During the climb, light frost was observed on the windshield. The aircraft reached FL 180 at 12:21, with an IAS of 150 kt and OAT around -15°C. The pilot requested clearance to climb to FL 200 to fly above the clouds. At 12:28, the climb began, reaching FL 200 at 12:31. The pilot observed light icing on the wing leading edges, estimated at half a centimeter thick, but did not activate the de-icing system. The autopilot began to struggle holding altitude, fluctuating ±100 ft with pitch variations.
At 12:34:43, the pitch attitude dropped to -3° with a vertical speed of -1,450 ft/min. The pilot detected a loss of altitude of 200-300 ft and made a nose-up input. After the aircraft returned to FL 200, the pilot disconnected the autopilot. The pitch attitude then increased to 5° nose-up. At 12:35:09, vertical speed reached +1,300 ft/min. The pilot applied nose-down stick and used the electric elevator trim, but it had no effect. He disconnected the electric trim and attempted manual trim, which seemed jammed. He pushed hard on the stick while reducing power, suspecting icing on the trim tabs or elevators. He declared an emergency at 12:35:50 and requested diversion to the nearest airport, choosing Châlons-Vatry. The front-seat passenger assisted in pushing the stick forward to descend. At 12:36:41, the pilot reported excessive vibration. The maximum IAS during descent was 214 kt. As the OAT increased during descent, control gradually returned. Full control was regained at about 4,500 ft with OAT +1°C. The pilot landed at Châlons-Vatry at 12:56 without further incident. Afterwards, a large dent was observed in the fuselage near the left engine.
Aircraft Information
The Cessna 340A is a pressurized twin-engine aircraft. Registration N340YZ is not approved for flight in known icing conditions, as indicated by a placard in the cockpit. It is equipped with propeller anti-icing, pitot heat, windshield de-icing (isopropyl alcohol), and pneumatic de-icing for wings and horizontal stabilizer. The elevator trim is controlled electrically or manually via a thumbwheel. The electrical trim actuator is in the tail.
Post-Incident Inspection
Examination of the airframe revealed a dent about 6 cm in diameter and 1 cm deep near the left engine, consistent with ice impact from a propeller blade. The propeller anti-icing system tested normal. Examination of the elevator and trim control mechanisms found no anomalies. Grease samples from the trim actuator showed normal characteristics and low water content, ruling out icing-related jamming. The investigations did not identify any factors that could explain in-flight jamming of the elevators or trim.