What happened
On 21 January 2021, a Bell 430 helicopter, registration ZT-RRT, was conducting an emergency medical flight from Midrand to Pietermaritzburg. The crew, which included a pilot, a paramedic, two doctors, and a nurse, was en route to collect a patient for specialized care. While cruising at approximately 725 feet above ground level along the N3 Highway, the aircraft experienced a sudden and catastrophic loss of control.
Eyewitnesses on the highway and nearby farms reported seeing the helicopter spinning rapidly and losing altitude. During the descent, large sections of the aircraft, including the tail boom and rotor blades, detached from the main structure. The helicopter impacted the ground near Winterton and was destroyed by a post-impact fire. There were 5 fatalities among the five people on board.
The investigation
SACAA AIID investigators examined the wreckage and analyzed flight data from a Spidertracks monitoring device. The investigation focused on the structural integrity of the rotor system and the maintenance history of the aircraft. Metallurgical analysis of the wreckage revealed that a fatigue crack had developed on the threaded section of a clevis component used in the pitch control lever of one of the main rotor blades.
Findings
Technical analysis established that the failure of the clevis on the pitch control lever was the primary cause of the accident. This mechanical failure caused the rotor disc to become unstable, which subsequently severed the rear section of the tail boom and led to the separation of the main rotor blades. This sequence of events rendered the aircraft uncontrollable.
Contributing factors included:
- Metal fatigue or corrosion fatigue within the clevis component.
- A failure to detect the existing fatigue crack during previous magnetic particle inspections and mandatory periodic maintenance.
- Maintenance inspections that did not sufficiently account for the impact of environmental factors, such as high humidity and chlorine, on the component's integrity.