Stall and terrain impact during mountain flight in Cessna 172

Casualties unknown • FR

A Cessna 172 crashed in the Pyrenees after a late attempt to turn around in a narrow valley, resulting in serious injuries to the pilot and passengers.

What happened

On October 8, 2006, a Cessna 172 M Skyhawk, registration F-GFCZ, was conducting a flight from Pamiers to Perpignan via the Pyrenees mountains. The flight included three passengers, and the pilot intended to fly over the village of Siguer.

As the aircraft entered a narrow valley near the Gnioure pond, the pilot attempted to perform a U-turn. Video footage from a passenger indicates that the stall warning activated while the aircraft was approximately 30 feet above a dam. Due to the narrowness of the valley, the pilot was unable to complete the turn and instead continued southward. During this maneuver, engine power decreased, and the stall warning became continuous, signaling a critical loss of airspeed. The aircraft stalled at a low altitude, struck the terrain on the left side, and overturned.

The investigation

The investigation examined radar data, video footage from the aircraft, and the aircraft's performance capabilities. Investigators established that while a turnaround was possible over the village of Siguer, the valley narrowed significantly as the aircraft progressed south.

Technical analysis revealed that the aircraft was operating near its maximum takeoff weight due to the significant fuel load on board. At the flight altitude, the available engine power was less than 60% of the maximum power available at sea level, due to the combination of high density altitude and a full-rich fuel mixture setting. Furthermore, the aircraft's theoretical maximum climb gradient at maximum weight was only 3.4 degrees, whereas the terrain gradient between the village and the dam was approximately 8 degrees.

Findings

  • The pilot made a late decision to execute a turnaround in the mountains.
  • There was an insufficient consideration of the reduced engine performance at high density altitude.
  • The pilot lacked adequate knowledge regarding the specific challenges and aerodynamic requirements of mountain flying.
  • The aircraft's heavy weight and the high altitude significantly degraded climb performance, making the required terrain clearance impossible during the maneuver.

Probable cause

The accident was caused by a late decision to turn around in a narrow valley, compounded by the pilot's failure to account for the significant loss of engine performance at high density altitude and the aircraft's heavy weight.

Frequently asked questions

What happened in the 2006-10-08 survenu le 8 octobre 2006 à l’avion accident near FR?

A Cessna 172 crashed in the Pyrenees after a late attempt to turn around in a narrow valley, resulting in serious injuries to the pilot and passengers.

What aircraft was involved and where did it happen?

The accident on 2006-10-08 involved a survenu le 8 octobre 2006 à l’avion, at FR.

What was the probable cause of the accident?

The accident was caused by a late decision to turn around in a narrow valley, compounded by the pilot's failure to account for the significant loss of engine performance at high density altitude and the aircraft's heavy weight.

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