What happened
On 28 November 2019, a Bell 505 helicopter, registration ZT-RDR, departed Kimberley Aerodrome for a private aerial inspection mission. The flight, which included the pilot and three passengers, was intended to survey the KEM-JV mine, Kamfers Dam, and local water supply pipelines under visual flight rules.
While flying near a military base in the Midlands area, the crew identified significant leaks in a main water pipeline. To facilitate photography of the leaks, the pilot descended to approximately 300 feet above ground level and slowed the aircraft's speed. During a right-hand turn to follow the pipeline, the helicopter experienced an uncommanded clockwise yaw. Despite the pilot's attempts to regain control through pedal and collective inputs, the aircraft entered a spin and struck an uneven surface near pipeline trenches. The impact resulted in substantial damage to the helicopter and four serious injuries to the occupants.
The investigation
SACAA AIID investigators examined the aircraft's flight data, including the Engine Electronic Control Unit (EECU) and Garmin G1000H logs, which showed no mechanical malfunctions prior to the impact. The investigation also reviewed the aircraft's weight and balance, finding that the takeoff weight of 3,708 lbs exceeded the maximum allowable weight of 3,680 lbs by 28 lbs.
Analysis of the flight dynamics revealed that the aircraft was operating at a low altitude and low airspeed, which prevented the successful execution of emergency autorotation procedures. Furthermore, the high density altitude at the time of the accident meant that available engine power was insufficient to assist in a recovery.
Findings
- The primary cause of the accident was the helicopter losing control during a right turn, leading to an impact with the ground.
- Loss of tail rotor effectiveness (LTE) occurred due to an increased main rotor angle of attack during the turn.
- The pilot utilized incorrect techniques during the right-hand maneuver.
- The aircraft was operating in an overweight condition.
- The low altitude and low airspeed prevented the pilot from performing the necessary emergency procedures to stabilize the rotor RPM.