What happened
On December 4, 2013, an Airbus Helicopters AS3/B3, registration F-GKMP, was conducting a flight training mission near Albertville, France. The flight, operated by SAF Industries, involved an instructor and a student pilot performing various maneuvers. After completing several exercises, the crew transitioned to a westward translation toward the summit of 'la dent du corbeau'.
As the aircraft reached a speed of approximately 40 knots, the instructor initiated a simulated hydraulic failure by pressing the 'TEST HYDR' button. This action triggered the hydraulic failure warning and an audible alarm. Immediately, the student pilot noted the helicopter began a slow leftward yaw. Despite attempts to use the pedals, the aircraft entered a full rotation. The instructor took control and attempted to reset the 'TEST HYDR' button to restore hydraulic assistance to the tail rotor pedals. However, the hydraulic failure warning remained active. Within seconds, the flight controls—including the cyclic and collective—became increasingly heavy. The aircraft subsequently struck the mountain summit at 7,500 feet, causing the helicopter to overturn and slide 150 meters down the slope. The impact resulted in two serious injuries to the crew and the total destruction of the aircraft.
The investigation
The BEA examined the wreckage and the aircraft's technical components. Investigators found that the tail boom had separated from the main fuselage, and the tail rotor and empennage were located several meters away. Analysis of the engine indicated power was being applied at the moment of impact.
Technical inspections of the flight computers (DECU and VEMD) showed no prior malfunctions, though a 'XPC' message regarding collective pitch was recorded at the time of the accident. While the servocommand and compensator functioned according to manufacturer specifications, investigators identified a deformation in the ball linkage caused by overload during the crash.
Crucially, the investigation focused on the hydraulic system's mechanics. The 'TEST HYDR' button was found in the 'off' position, but the 'HYD' switch on the collective lever was set to 'off'. This switch, when turned off, cuts the hydraulic circuit to balance residual pressures, making it impossible to repressurize the tail rotor accumulator.
Findings
- The training exercise was initiated during a non-stabilized flight phase; the instructor pressed the 'TEST HYDR' button at 40 knots, which is below the recommended safety speed of 40–60 knots for such maneuvers.
- At this low speed, the aerodynamic effectiveness of the vertical fin was insufficient to counteract the yawing moment, making the pedals too heavy for the student to manage.
- The student pilot had turned the hydraulic cut-off switch to the 'off' position, which prevented the instructor from successfully restoring hydraulic pressure to the tail rotor pedals.
- A lack of detailed coordination during the pre-flight briefing regarding the specific sequence of the hydraulic failure simulation contributed to the uncoordinated actions of the crew.