Johannesburg is a medium sized city that located at the south Africa and is one of the three capitals of the country along with Bloemfontein and Pretoria. business and the tourism in this city is low around 100-270(sometimes 270-300).
The default airport is "O.R Tambo Int'l Airport".
The rather isolated location of Johannesburg and South Africa makes it hard starting in Johannesburg as it far away from many major cities other than inside South Africa (the closest being Lagos. in Nigeria) so short range aircraft such as the CRJ and E-Jet families are not suited to Johannesburg. The default airport in Johannesburg meets the demand for the city, rarely filling up towards the end of the game.Thus, a secondary airport is not needed. Buying the national airport could be profitable if bought in the around the mid-late 80s. Johannesburg maybe bad for short range flights but it's strategic position between south Asia and South America mean that many players use Johannesburg as a base for stopovers e.g Singapore-Johannesburg- Sao Paulo.