What happened
On 16 October 2015, a Guimably Cabri G2 helicopter, registration ZS-HII, was involved in an accident on a farm near Kleinberg, west of Mossel Bay. The pilot, a student undergoing training to obtain a commercial license, was conducting solo maneuvers in an open area of farmland. After successfully completing a clockwise hover turn, the pilot attempted an anti-clockwise 'spot turn'.
During this maneuver, the helicopter's skid gear made contact with the ground. As the aircraft continued to rotate, the tail rotor stinger and the lower vertical fin assembly struck the earth. The impact was severe enough to cause the vertical fin and the shrouded fenestron tail rotor assembly to break away from the composite tail boom. Following several uncontrolled rotations, the helicopter crashed nose-down approximately 48 meters from the initial impact point, coming to rest on its right side. The pilot sustained a minor injury to her shoulder and a blow to the head, but was able to exit the wreckage unassisted.
The investigation
SACAA AIID investigators examined the wreckage and the flight history of the aircraft. The investigation confirmed that the Guimbal Cabri G2 was in a good mechanical state, with only 80 hours of total time since new. All mechanical failures identified, including the shearing of the tail rotor drive shaft due to torsional overload, were directly attributed to the impact with the ground.
Investigators also reviewed the pilot's experience and the environmental conditions. At the time of the accident, weather conditions were clear with light winds from the southeast at 8 to 10 knots. The investigation also noted that while the pilot was flying within the weight and balance limits, certain cockpit configurations posed secondary risks during the impact sequence.
Findings
- The primary cause of the accident was the pilot allowing the lower vertical fin to contact the ground during a low-altitude maneuver.
- The contact caused the separation of the tail rotor assembly, leading to a total loss of tail rotor thrust.
- The loss of control was worsened by the pilot increasing the collective pitch during the rotation, which increased the torque effect.
- The maneuver was performed at a height of less to than one meter, leaving almost no margin for error.
- The pilot was not wearing a flying helmet at the time of the accident.
- The position of the portable fire extinguisher and an unsecured POH bag were identified as potential safety hazards within the cabin.
Safety action
Following the investigation, several safety recommendations were addressed. The training organization implemented a requirement for the pilot to undergo evaluation flights with an instructor. Additionally, the investigation highlighted the need for better security for cockpit items, such as the POH bag, to prevent them from striking occupants during uncommanded rotations. The report also suggested reviewing the placement of portable fire extinguishers to ensure they do not interfere with flight controls during an emergency.