Why Grand Central Airport is not in the passenger airport comparison
Operator documentation and the SACAA aerodrome register describe Grand Central Airport as a base for flight schools, corporate charters, and visiting general aviation aircraft rather than scheduled ticketed airline flights. On the map, Grand Central Airport (GCJ / FAGC) sits 26 km from Johannesburg and 27 km from Pretoria, which is why it can appear geographically closer than a commercial terminal while serving a different aviation purpose.
For travellers flying commercially to Johannesburg, the closest airport in TownWing’s 18-airport passenger comparison is O.R. Tambo International Airport (JNB), which sits 21 km from the Johannesburg reference point and 20 km from Grand Central Airport when measured airport-to-airport.