13.towered-vs-non-towered. Towered vs. Non-Towered Airports
U.S. airports fall into two broad operational categories: towered and non-towered. The distinction determines who is responsible for traffic separation, how communications are conducted, and what authority a pilot must obey before taxi, takeoff, or landing.
Towered Airports
A towered airport has an operating Air Traffic Control Tower (ATCT). At these fields, an ATC clearance or instruction is required for movement on the runway, takeoff, landing, and (at most Class B, C, and D fields) taxiing. The pilot in command must establish two-way radio communications with the tower before entering the surface area or Class D airspace, and must comply with all ATC instructions per 14 CFR 91.123 (or request an amended clearance if unable).
Typical tower frequencies and services include:
- ATIS (Automatic Terminal Information Service) — recorded broadcast of weather, active runway, NOTAMs, and approach in use. Monitor before initial contact.
- Clearance Delivery — issues IFR clearances and, at busier fields, VFR departure clearances.
- Ground Control — controls movement on taxiways and inactive runways.
- Local Control (Tower) — controls runways and the airspace within roughly 4 NM and up to 2,500 ft AGL of the airport.
A towered airport is depicted on sectional charts in blue. The tower frequency (CT) is listed with a circled "C" indicating common traffic advisory frequency when the tower is closed. Many control towers are part-time; when the tower closes, the airport reverts to non-towered procedures and the CTAF becomes the tower frequency.
Non-Towered Airports
A non-towered airport has no operating control tower (or the tower is closed). Roughly 80% of U.S. public-use airports are non-towered. There is no ATC clearance to taxi, take off, or land — the pilot in command is responsible for traffic separation, sequencing, and collision avoidance using see-and-avoid and standard self-announce procedures.
Key concepts:
- CTAF (Common Traffic Advisory Frequency) — the radio frequency used for self-announcing position and intentions. Identified on the sectional chart by a magenta circled "C" next to the frequency.
- UNICOM — a non-government air-to-ground service (typically the FBO) that may provide advisories, fuel requests, and field conditions when staffed. UNICOM is often the same frequency as CTAF.
- MULTICOM (122.9 MHz) — used as the CTAF at airports with no UNICOM.
- AWOS/ASOS — automated weather, when available, replaces ATIS.
Non-towered airports are depicted in magenta on sectional charts.
Recommended Communication Procedure (AC 90-66B)
FAA Advisory Circular 90-66B recommends self-announcing on CTAF at the following points:
- 10 NM out, inbound
- Entering the traffic pattern (typically a 45° entry to the downwind at pattern altitude)
- On downwind, base, and final
- Clear of the active runway after landing
- Taxiing onto the active runway for departure
- Departing the pattern
The standard format is: airport name, aircraft call sign, position/intention, airport name — for example: "Lincoln traffic, Skyhawk 12345, ten miles south, inbound for landing runway 18, Lincoln." Bracketing the transmission with the airport name prevents confusion with nearby fields sharing the frequency.
Traffic Pattern Differences
At towered airports, the tower assigns the pattern, runway, and sequence — a pilot may be cleared for a straight-in, base entry, or extended downwind as traffic dictates.
At non-towered airports, the standard pattern is left traffic at 1,000 ft AGL (varies by aircraft type and field), entered on a 45° leg to the midpoint of the downwind. Right traffic is used only where indicated by the chart supplement, segmented circle, or visual indicators (light gun signals do not apply). Pilots should avoid straight-in approaches when other aircraft are in the pattern, per AC 90-66B.
Light Gun Signals
If radio communication is lost at a towered airport, the tower uses light gun signals (steady green = cleared to land/takeoff; flashing red = taxi clear of runway in use; etc.). At non-towered airports, light gun signals do not apply — pilots simply continue using see-and-avoid and visual signals.
Pilot Responsibilities Summary
- Towered: Obtain clearance, comply with ATC, monitor ATIS, read back hold-short and runway-crossing instructions verbatim.
- Non-towered: Self-announce on CTAF, fly the published or standard pattern, yield to aircraft on final, and remain especially vigilant for NORDO (no-radio) traffic, which is legal at most non-towered fields.
Understanding which category an airport falls into — and the procedural shift that occurs when a part-time tower closes — is fundamental to safe arrivals and departures throughout the National Airspace System.