18 June 1911
In 1907, four years prior to flying on his aeroplane in Kimberley, John Weston embarked on the construction of his own aeroplane in Brandfort, in the Orange Free State (now known as Free State). Weston lacked an engine with adequate power so he dismantled the aircraft and shipped it to France. While in France he fitted a Gnome rotary engine (50hp) and flew it successfully in 1910. On 18 June 1911 Weston flew the first flight in Kimberley creating a South African a flight record of eight-and-a-half minutes in his Weston-Farman biplane. Fearing numerous attempts of this nature, the Aeronautical Society of South Africa was established 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 travelling to 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 the first flight of this aircraft.
References

Anon, (n.d.), ‘Brandfort’from Routes [online] Available at www.routes.co.za[Accessed: 15 June 2011]|Anon,(n.d.), ‘Early Flying in South Africa’from The Aero Club of South Africa [online] Available at www.sapfa.org.za[Accessed: 13 June 2011]|Anon, (n.d.), ‘First aeroplane flight in Kimberley breaks the nonstop record’ from South African History Online [online] Available at www.sahistory.org.za[Accessed: 13 June 2011]