What happened
On Saturday, October 17, 1998, a Cessna 172H, registration F-BOQA, was conducting a local flight near the Andernos-les-Bains aerodrome. During the final turn of the flight, the aircraft's left wing dropped, leading to a sudden and steep nose-down attitude. In an attempt to recover, the pilot increased engine power. While the aircraft regained altitude, it struck the tops of several trees during the maneuver. The pilot was able to complete the landing without further incident, though the aircraft sustained slight damage.
The investigation
The investigation focused on the circumstances leading to the loss of control and the pilot's interpretation of the flight instruments. Investigators examined the aircraft's airspeed indicator, noting that the instrument featured a dual-scale design: knots (kt) were displayed on the inner ring, while miles per hour (mph) were displayed on the outer ring. The pilot, who had 378 total flight hours, provided testimony regarding the instrument's layout.
Findings
The primary cause of the loss of control was an error in reading the airspeed indicator. The pilot stated that they were accustomed to using other aircraft where the outer ring of the anemometer is graduated in kilometers per hour (km/h). This familiarity led to a confusion between the scales during the critical phase of the flight, resulting in an incorrect assessment of the aircraft's airspeed during the turn.