Definition
An unstaffed, remotely controlled ground-to-ground communications facility installed at airports without an operating control tower or after tower hours. Pilots use the GCO on the ground to contact the nearest Air Traffic Control facility or Flight Service Station via VHF radio, which the GCO then connects through a telephone link. It is intended primarily for activating or closing IFR flight plans and obtaining IFR clearances or weather briefings while on the ground.
Plain English
A radio-to-phone box at an airport that lets a pilot on the ground talk to Air Traffic Control or Flight Service when there is no tower nearby. The pilot keys the radio a set number of times, and the GCO automatically dials ATC or Flight Service over a phone line.
Context Anchor
Seen on airport information pages and used at some non-towered airports before departure or after landing.
Derivation
The name describes its function plainly: a ground-based outlet for communication. 'Outlet' here is used in the sense of an access point, like an electrical outlet on a wall — a fixed place where you plug in to reach a service that lives elsewhere.
Why Pilots Care
It provides access to essential flight services at remote or unattended airports where direct phone or tower contact is unavailable.
Analogy
Think of a GCO like a radio-based phone connection for pilots. You talk on the aircraft radio, and the system connects that call to the service you need.
Intuition Check
Do not think of a GCO as an electrical outlet or a staffed radio station. In this context, an outlet is a communication access point that connects your aircraft radio to air traffic control or Flight Service.
Example Sentence 1
Before departing the non-towered field, the pilot used the GCO to call Flight Service and pick up his IFR clearance.
Example Sentence 2
After landing at the unattended airport, she used the GCO to close her VFR flight plan.