What happened
On January 31, 2007, a Beechcraft 58 Baron, registration F-GNSI, was conducting an instrument multi-engine training flight from Saint-Yan to Dole. During the descent, the aircraft entered a cloud layer at approximately 3,000 feet, encountering heavy opaque icing. While the crew activated anti-icing systems for the propellers and windshield and utilized pneumatic de-icing boots on the leading edges, ice continued to accumulate on the airframe.
Following a missed approach due to poor visibility, the instructor simulated an engine failure by reducing power on the right engine. As the student pilot continued the approach and reduced power on the remaining engine, he noted an inability to maintain directional control. Upon taking control, the instructor discovered that the rudder was jammed. After applying significant force to the pedals, a cracking sound was heard, and the rudder released, causing the aircraft to yaw abruptly. The crew continued the single-engine approach and landed safely.
The investigation
The investigation focused on the flight conditions and the mechanical state of the flight controls during the engine failure maneuver. Investigators established that the aircraft had been operating in icing conditions for approximately twenty minutes between the missed approach and the final approach. The investigation examined the effectiveness of the active de-icing systems and the impact of ice accumulation on the movable control surfaces.
Findings
- The primary cause of the incident was the decision to initiate and continue an engine failure training exercise while encountering significant ice accumulation.
- Ice had accumulated on the rudder surface, leading to the mechanical blockage of the control surface.
- The crew continued the simulated emergency procedure despite visible ice buildup on the airframe.
Safety action
Following the event, the flight school issued an operational notice emphasizing that even for aircraft certified for known icing conditions, significant ice accretion is a serious hazard that necessitates exiting the icing environment if possible. The notice specifically stated that training exercises involving asymmetric thrust or aerodynamic changes, such as engine failure drills, should not be undertaken during active icing. Furthermore, the notice recommended that crews periodically manipulate all flight controls in icing conditions to check for any binding or blockages.