What happened
On August 1, 1998, a Cessna 172C, registration CS-AKF, operated by ATA (Aerocondor Transportes Aéreos, Lda.), was involved in an accident during taxi operations at Cascais Aerodrome, Portugal. The aircraft was scheduled for a specialized aerial surveillance mission for the GNR (National Republican Guard) involving road traffic monitoring on the 25 de Abril Bridge.
Upon arrival at the aerodrome, the pilot was informed of significant wind conditions, with winds from 020 degrees at 30 knots and gusts up to 40 knots. During the taxi sequence toward the holding point for runway 35, the pilot attempted to maneuver the aircraft via taxiway Bravo. However, the strong tailwind component made directional control extremely difficult, as the wind force exceeded the effectiveness of the aircraft's braking system.
In an attempt to find a more manageable route, the pilot decided to return to the parking area. While taxiing on runway 17 with a tailwind, the aircraft's flaps unexpectedly deployed to the full position. This sudden movement caused the aircraft to pitch forward, lifting the main landing gear off the pavement. The aircraft immediately settled, causing the propeller to strike the runway surface while the engine was running at 1,000 RPM. The impact resulted in damage to the propeller and the leading edges of both wings.
The investigation
The GPIAAF investigation focused on the environmental conditions and the operational limits of the aircraft and operator. The investigation established that the wind at the time produced a significant crosswind component of approximately 15 to 18 knots for runway 35.
Investigators examined the approved flight manual for the Cessna 172C and the ATA company operations manual, noting that neither document specified maximum wind velocity limits for taxi or takeoff operations. Furthermore, a physical inspection of the aircraft revealed that the flaps could be moved to the full position with minimal downward force, which contributed to their unexpected deployment under wind pressure.
Findings
- The primary cause of the accident was the pilot's inability to maintain control of the aircraft due to the extreme wind conditions present during taxi.
- The aircraft was operating in high-wind conditions (30 knots with 40-knot gusts) that created significant directional instability.
- Neither the manufacturer's flight manual nor the operator's manual provided specific operational wind limits, leaving the decision-making entirely to the pilot's discretion.
- The unexpected deployment of the flaps to the full position caused a sudden change in the aircraft's pitch, leading to the main gear lifting and the subsequent propeller strike.
- There was potential subjective pressure on the pilot to complete the scheduled surveillance mission.