They have completed their probe into the May incident, which claimed the lives of pilot Derek Fitzgerald and student pilot Richard Morgan. 

The Civil Aviation Authority has published the details of its findings on its website. 

READ: WATCH: Helicopter crashes into Umgeni River

Investigators say the pair took off on a training flight from Virginia Airport in the Starlite Aviation Group chopper without incident. 

But as the helicopter approached Umgeni River, a bird hit the tail rotor blade, causing the aircraft to spin out of control and crash into reeds on the river bank. 

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The blade subsequently cut through the tail cone skin, and in the process, several other parts were severed.

The CAA says an eyewitness saw a number of medium-sized birds flying in the direction of the chopper before it came down. 

Investigators noted bird feathers and blood on one of the rotor blades.