Tower vs ARTCC vs TRACON

Towers handle airport operations, ARTCCs/En-route handle cruise phase, and TRACONs handle climbing and descending aircraft, as well as aircraft transiting between ARTCCs in their controlled areas.

Tower and TRACON

TRACON may be on a separate site or colocate with a tower. For example, California has 5 TRACON, 3 of them colocate with a tower (Santa Barbara, Fresno, Bakersfield) and 2 are independent (Northern California TRACON, near Sacramento; Southern California TRACON, near San Diego).

Clearance Frequency

Clearance Delivery Frequency is initial clearance from ATC before you take off.