ICAO Annex 2
CHAPTER 1. DEFINITIONS

Aerodrome traffic zone. An airspace of defined dimensions established around an aerodrome for the protection of aerodrome traffic.

SA CIVIL AVIATION REGULATIONS
PART 91: GENERAL AVIATION AND OPERATING FLIGHT RULES
91.06.12 Operation on and in vicinity of aerodrome

(2) If an aerodrome control tower is in operation, the PIC shall also, whilst the aircraft is within the aerodrome traffic zone

(a) maintain a continuous radio watch on the frequency of the aerodrome control tower responsible for providing aerodrome control service at the aerodrome, establish two way radio communication as necessary for aerodrome control purposes and obtain such clearances for his or her movements as may be necessary for the protection of aerodrome traffic; or (…)

Which is only for use by military aircraft. → INCORRECT. Aerodrome traffic zones are for all aircraft operating at the aerodrome, not exclusively military.

Where no radio communication is required at any time. → INCORRECT. Communication with the aerodrome control unit is required (SACA 91.06.12).

Which is controlled airspace and where aerodrome control is in operation. → CORRECT. An Aerodrome Traffic Zone is a designated portion of controlled airspace around an aerodrome to protect aircraft during takeoff, landing, and circuit operations.

Which extends 50 NM from the aerodrome at all times. → INCORRECT. Aerodrome traffic zones have a limited radius, typically around 2–5 NM, not 50 NM and not always the same with each other.