Definition
The radio frequency assigned as the main communication channel between a pilot and a specific air traffic control facility or service for a given phase of flight. It is the frequency the pilot is expected to monitor and use first, before resorting to any backup or secondary frequency.
Plain English
The main radio channel a pilot is told to use to talk to a particular controller or station. Other frequencies may be available as backups, but this is the one to use first.
Context Anchor
Seen in airport information, chart listings, radio communication procedures, and air traffic control facility information.
Derivation
Primary comes from the Latin primus, meaning first. The primary frequency is simply the first-choice frequency for that controller or service.
Why Pilots Care
Using the assigned primary frequency keeps the pilot in contact with the right controller. Switching to a secondary frequency without reason can mean missed calls, missed traffic, or missed instructions.
Intuition Check
Primary does not mean it is the only frequency that can work. It means it is the main frequency normally used first for that facility or situation.
Example Sentence 1
Approach assigned us 124.35 as the primary frequency, with 121.5 available as a backup if we lost contact.
Example Sentence 2
When checking weather at the destination, the pilot first called on the primary frequency listed in the chart supplement.