What happened
On October 3, 2001, at approximately 16:30, a Robinson R22 helicopter, registration 3A-MLE, was conducting a navigation training flight from Monaco to Barcelonnette and back. The crew, consisting of an instructor and a student pilot, departed Barcelonnette heading east toward the Col de Fours. During the climb, the instructor noted a decrease in rotor RPM and attempted to increase collective pitch to compensate. This triggered the low rotor RPM warning alarm.
As the aircraft climbed along the steep terrain, the instructor observed an admission pressure of 23 inches of mercury and a climb rate of 300 feet per minute, while the student noted a slower climb rate between 0 and 200 feet per minute. Due to the lack of sufficient lift, the crew was forced into an emergency landing. The low altitude at the time the alarm sounded prevented the execution of an autorotation, resulting in a heavy impact on a slope below the flight path. The aircraft was destroyed.
The investigation
The investigation focused on the engine performance and the environmental conditions at the time of the accident. While the aircraft was operating within the manufacturer's takeoff limits for its weight and the ambient temperature of 22°C, investigators examined the engine for mechanical failures. The examination of the engine revealed no malfunctions that contributed to the loss of power.
Investigators also analyzed the meteorological conditions, noting that while the takeoff was within limits, the aircraft was operating in a high-altitude mountain environment. The flight path chosen for the return leg was different from the safer route suggested by the club's chief pilot, which would have followed the Ubaye Valley to ensure a safer climb gradient.
Findings
- The primary cause of the accident was an inappropriate flight route relative to the aircraft's performance capabilities in mountainous terrain.
- The steep terrain gradient and the rapid decrease in air density contributed to the loss of performance.
- Moderate to strong turbulence and downdrafts on the leeward side of the slope further impacted the aircraft's ability to maintain altitude.
- The aircraft was operating at the edge of its power limits during the climb.