Class C service requires pilots to establish two-way radio communications before entering Class C airspace. If the controller responds to a radio call with, “(a/c call sign) standby,” radio communications have been established and the pilot can enter Class C airspace.

To legally enter Class C airspace, a pilot must establish two-way radio communication with the appropriate Air Traffic Control (ATC) facility, typically the "Approach Control" for that specific area. According to FAA regulations, "two-way communication" is officially established when the controller responds to the pilot's initial call by using the aircraft's specific tail number or call sign. If the controller says "Aircraft calling, stand by," the pilot has not established communication and must remain outside the Class C boundary. Additionally, the aircraft must be equipped with a functional Mode C or Mode S transponder with altitude reporting capabilities and ADS-B Out equipment. Before entering, the pilot must also be tuned to the correct frequency and provide the controller with their current position, altitude, and destination or intentions. Once the controller acknowledges the specific tail number, the pilot is cleared to enter the "inner circle" (usually a 5-mile radius) and the "outer circle" (a 10-mile radius) of the airspace, provided they follow all subsequent ATC instructions for traffic separation.