Definition
An unstaffed VHF/UHF radio transmitter and receiver site, located away from an air route traffic control center (ARTCC), that extends the controller's radio coverage so they can talk to aircraft flying through areas the center's main antennas cannot reach. The remote site is linked back to the controller by landline or microwave so the controller can speak and listen through it as if they were transmitting locally.
Plain English
It's a remote radio relay site that lets an en route controller talk to aircraft that are too far away or too low for the main center antennas to hear. The pilot just talks on the assigned frequency; the radios at the remote site pass everything back to the controller.
Context Anchor
Pilots may encounter RCAGs indirectly when using published air traffic control frequencies, especially when talking to Center or another controller over a wide area.
Derivation
"Remote" because the radio site is located away from the controller. "Air/Ground" is the standard term for two-way radio communication between aircraft and a ground station. Together it means a ground-based radio site, sitting out in the field, that the controller uses by remote control.
Why Pilots Care
It extends reliable two-way radio contact into remote or obstructed areas, preventing loss of ATC communication during cross-country flights.
Intuition Check
“Remote” does not mean the pilot controls the facility. It means the radio equipment is located away from the controller and is operated as part of the control system.
Example Sentence 1
Center handed me off to a different frequency as I crossed the ridge, since the previous RCAG no longer had good coverage of my area.
Example Sentence 2
Controllers routed the flight to the nearest RCAG site when the primary transmitter could no longer reach the aircraft.