What happened
On 30 January 2020, a Cessna 310 R, registration N443LT, was conducting a short IFR familiarization flight between Toussus-le-Noble and Pontoise Cormeilles-en-Vexin. The crew consisted of an instructor and a pilot receiving training. While flying in cloud cover at approximately 3,000 ft, the aircraft experienced significant altitude fluctuations.
During the cruise phase, the pilot receiving training attempted to stabilize the aircraft using the electric elevator trim. This resulted in an excessive nose-down input combined with a manual nose-down stick movement. The aircraft entered a rapid descent, dropping from 3,300 ft to 1,050 ft with a calculated mean vertical speed of approximately -4,800 ft/min. At one point, the aircraft reached an altitude of 600 ft, triggering a Minimum Safe Altitude Warning (MSAW) on the Paris-CDG controller's radar.
As the aircraft emerged from the clouds, the instructor took control to perform a recovery pull-up maneuver. The aircraft subsequently climbed back to 3,000 ft and completed the flight as planned, performing approaches at Pontoise before returning to Toussus-le-Noble.
The investigation
The BEA examined radio communications, radar data, and statements from the crew. The investigation focused on the sudden change in flight path and the pilot's interaction with the aircraft's controls. Investigators analyzed the aircraft's equipment, specifically the dual elevator trim system, which includes both a mechanical control wheel and an electric double rocker switch located on the left-seat stick.
Findings
Several factors contributed to the altitude excursion:
- The pilot receiving training had not flown for nine months since obtaining his CPL.
- The pilot was unfamiliar with the specific handling characteristics and the electric elevator trim system of the Cessna 310 R, having previously trained on different aircraft types.
- The instructor's reaction to correct the aircraft's attitude was delayed.
- The pilot's attempt to use the electric trim resulted in an excessive and uncoordinated input during a period of high workload.