Final answer:
Pilots must contact the control tower before entering the control zone of an airport with an operating tower to ensure safe and efficient management of air traffic.
Step-by-step explanation:
When approaching an airport with an operating control tower, you must contact the tower before entering the control zone. The control zone is an area around the airport defined by certain boundaries that are established to manage the flow of air traffic in the vicinity of the airport. It is crucial for safety reasons to establish communication with the control tower to obtain clearance and instructions for approaching or departing the airspace. This process ensures that air traffic controllers can manage all traffic efficiently, preventing collisions and providing timely guidance to pilots.