What happened
On 2 January 2021, an AS350-B3 helicopter, registration ZS-OXK, was preparing for an anti-crime patrol flight from Cape Town International Airport to the Cape Peninsula National Park. While the pilot was waiting for takeoff clearance from air traffic control, he briefly removed his hand from the collective pitch lever to adjust the radio volume.
During this moment, the collective pitch lever moved to its maximum position, causing the cyclic to become extremely stiff and difficult to manipulate. As the aircraft lifted to approximately 30 feet above ground level, it began to yaw left with a forward pitch and right roll. The pilot attempted to use the yaw pedals to correct the movement, but they were ineffective. The helicopter completed two full rotations before the main rotor blades struck the ground. The subsequent impact caused a dynamic rollover to the right, and a fire broke out in the engine compartment. The pilot sustained minor injuries and was able to exit the aircraft unaided.
The investigation
SACAA AIID investigators examined the aircraft's systems and the pilot's pre-flight actions. Post-accident testing confirmed that the hydraulic system components were fully serviceable and that the loss of hydraulic fluid was a direct result of the impact. Data from the engine monitoring systems indicated that the engine failure occurred only after the aircraft hit the ground. The investigation also noted that a nearby Cessna C172 sustained damage from debris flying from the crash site.
Findings
- The pilot performed hydraulic system tests during pre-takeoff checks, which involved toggling the "HYD TEST" push-button.
- It is probable that the pilot failed to return the "HYD TEST" push-button to the OFF position before engaging the hydraulic cutoff switch on the collective lever.
- This oversight resulted in a lack of hydraulic pressure to the servos.
- When the pilot released the collective lever, centrifugal and natural forces pushed the lever to its maximum position, rendering the aircraft uncontrollable.
- The pilot may have been too preoccupied with the sudden loss of control to notice cockpit warning lights or audible alarms.