Definition
A mobile aeronautical service performed on the frequency 122.9 MHz to provide air-to-air communications between pilots operating at airports that have no tower, no Flight Service Station, and no published Unicom frequency.
Plain English
A radio frequency (122.9 MHz) that pilots use to talk to each other when flying into or out of a small airport that has no control tower and no ground radio station of its own.
Context Anchor
Seen in airport information listings and used by pilots at many small airports when announcing position, movement, or intentions.
Derivation
From 'multi-' (many) and 'com' (short for communication). The name reflects that the frequency is shared by many pilots at many small airports, not tied to any single station on the ground.
Why Pilots Care
Provides a standard way for pilots to coordinate traffic patterns and avoid conflicts at airports without staffed services.
Intuition Check
Do not think of Multicom as a private company radio or a general chat channel. It is a shared aviation frequency for short, necessary operational calls.
Example Sentence 1
Approaching the small grass strip, the pilot announced on Multicom, 'Traffic, Cessna 1234 entering left downwind for runway 18.'
Example Sentence 2
All aircraft in the area switched to Multicom to report their altitudes and locations.