18 June 1911
John Weston, a civil engineer, began the construction of his own aeroplane in 1907 at Brandfort, in the Free State. This was the first South African built aeroplane. He lacked an engine with enough power so he dismantled the aircraft and shipped it to France. It is possible that John Weston based his design on a Voisin. In France he fitted a Gnome rotary engine (50hp) and flew it successfully (in France) in 1910. On 16 June 1911 John Weston made the first flight in Kimberley establishing a South African non-stop flight record of eight-and-a-half minutes in his Weston-Farman biplane. His energy and drive led to the formation of the Aeronautical Society of South Africa in 1911. It was the start of the John Weston Aviation Company of South Africa, which did much to popularise flight in the country by touring the main centres and offering flights to the public. The dates of 6 June 1911 and 16 June 1911 are respectively given in two other sources for this event.
References

Wallis, F. (2000). Nuusdagboek: feite en fratse oor 1000 jaar, Kaapstad: Human & Rousseau.|Potgieter, D.J. et al. (eds)(1970). Standard Encyclopaedia of Southern Africa, Cape Town: NASOU, v. 1, p. 609-10.|The History of Aviation in South Africa. Website: sapfa.org.za