Serious incident to the Cessna 340 registered N340YZ on 06/02/2022 en route

While preparing the flight, a very heavy rain shower meant that the pilot had to interrupt refuelling. The tail unit was then exposed to sustained rain. After take-off from Lille-Lesquin in the rain, the pilot reported that he identified the presence of ice deposits on the windshield during the climb, and on the leading edge of the wings when he was in level flight at FL 200. However, the thickness of these deposits was still not sufficient, according to the pilot, to activate the pneumatic de-icing devices on the leading edges.

Flight parameters revealed fluctuations in altitude and speed during level flight at FL 200. The pilot reported that the elevator trim electrical control was no longer effective and that the manual control was jammed. The examinations carried out did not reveal any element likely to explain this jamming. It is probable that the elevator trim was jammed by water that solidified during the climb to FL 200, performed at an average indicated airspeed of 130 kt.

This probably impaired the autopilot's altitude hold function and caused abnormal pitch fluctuations that led the pilot to disengage the autopilot and perform a rapid descent to an altitude band where positive temperatures prevailed. The indicated airspeed was approximately 200 kt during the descent. The pilot, aided by his passenger, had to exert a considerable nose-down force on the stick until the aeroplane descended to an altitude of around 4,500 ft where there were positive temperatures. The elevator trim manual, then electrical control became operational again.