What happened
On February 6, 2022, a private Cessna 340A, registered N340YZ, departed Lille-Lesquin for Aix-les-Milles under an IFR flight plan. During the climb, the pilot noted frost on the windshield. Upon reaching FL 200, the pilot observed approximately half a centimeter of ice on the wing leading edges. At this altitude, the aircraft's pitch attitude began to fluctuate, and the autopilot struggled to maintain altitude.
As the aircraft's pitch attitude reached a minimum of -3°, the pilot attempted to correct the descent using the electrical elevator trim. When the electrical control failed to respond, the pilot attempted to use the manual trim thumbwheel, but found it was jammed. To manage the situation, the pilot disconnected the autopilot and performed an emergency descent to reach warmer air. The pilot and a passenger both applied significant physical force to the control stick to maintain a nose-down attitude. During the descent, the aircraft experienced heavy vibrations, and the pilot reported a dent in the fuselage caused by ice shedding from a propeller. The aircraft eventually reached warmer air below FL 50, where the controls regained functionality, allowing the pilot to land safely at Châlons-Vatry.
The investigation
The BEA examined the aircraft's flight control mechanisms, including the elevator and trim cables, pulleys, and the electrical actuator. Laboratory analysis of the grease in the trim actuator showed low water content, which ruled out the actuator itself freezing. The investigation also noted that during pre-flight refueling, a heavy rain shower had exposed the tail unit to sustained moisture. While the examination of the airframe did not find a mechanical defect, the investigators considered the possibility of ice formation within the control mechanisms.
Findings
- The aircraft was flying in conditions where ice had accumulated on the wing leading edges.
- The elevator trim was likely jammed by water that solidified during the climb to FL 200.
- The pilot's decision to descend to warmer altitudes was effective in restoring control of the aircraft.
- The aircraft's registration, N340YZ, was noted as being unauthorized for flight in known icing conditions due to the lack of an electrically heated windshield.