Helicopter tail boom breaks during uncontrolled yaw at Augsburg airfield

Casualties unknown • Verkehrslandeplatz Augsburg, DE

A training flight in a Cabri G2 ended in significant damage after the aircraft experienced an uncontrolled yaw during hovering exercises, causing the main rotor to strike the vertical fin.

What happened

On February 1, 2014, a Cabri G2 helicopter was conducting a training flight at the Augsburg airfield in Germany. The flight, intended for private pilot training, was delayed due to special VFR conditions and incoming traffic. To make use of the time, the flight instructor decided to perform hovering exercises with the student pilot.

During the maneuvers, the student pilot positioned the helicopter at a height of approximately 2 meters over a grass area known as the X-Ray Area. While the aircraft was in a stationary hover, it began to rotate uncontrollably to the right around its vertical axis. Despite the student's attempts to use the left anti-torque pedal, the rightward rotation accelerated. The instructor attempted to regain control by applying left pedal and increasing forward airspeed, but the proximity of obstacles forced him to abort the maneuver. To prevent a more serious collision, the instructor intentionally landed the helicopter on the ground. During this touchdown, the tail boom pitched upward, causing the main rotor to strike the upper portion of the vertical fin.

The investigation

The BFU examined the wreckage and the flight sequence. The investigation confirmed that the helicopter sustained heavy damage, including a broken tail boom and a severed section of the vertical fin. The Fenestron blades were also damaged. The investigation also reviewed the mechanical state of the anti-torque system, finding that the Fenestron pitch control mechanism was functioning correctly and was properly connected to the pedals.

Findings

  • The aircraft experienced an uncontrolled rotation to the right, which is the same direction as the main rotor's rotation.
  • According to manufacturer assessment, this indicates that the Fenestron was active with blades set at a high efficiency, generating more thrust for anti-torque compensation than was necessary, thereby driving the rotation.
  • There were no injuries to the pilot or the student pilot.
  • The aircraft was operated by a certified flight training organization with its own maintenance facility.

Probable cause

The helicopter experienced an uncontrolled yaw in the direction of the main rotor's rotation, likely because the Fenestron was generating excessive anti-torque thrust, leading to a loss of directional control during a low-altitude hover.

Frequently asked questions

What happened in the 2014-02-01 Hélicoptères Guimbal Cabri G2 accident near Verkehrslandeplatz Augsburg, DE?

A training flight in a Cabri G2 ended in significant damage after the aircraft experienced an uncontrolled yaw during hovering exercises, causing the main rotor to strike the vertical fin.

What aircraft was involved and where did it happen?

The accident on 2014-02-01 involved a Hélicoptères Guimbal Cabri G2, at Verkehrslandeplatz Augsburg, DE.

What was the probable cause of the accident?

The helicopter experienced an uncontrolled yaw in the direction of the main rotor's rotation, likely because the Fenestron was generating excessive anti-torque thrust, leading to a loss of directional control during a low-altitude hover.

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