Definition
A VHF radio frequency designated by the FCC and FAA as a multicom frequency, used by pilots for air-to-air communication and self-announcing position and intentions at airports without a control tower, FSS, or assigned UNICOM frequency.
Plain English
A shared radio channel pilots use to talk to each other and announce what they're doing at small airports that have no tower or other dedicated frequency.
Context Anchor
Seen in airport communication information, chart supplements, and FAA discussions of radio calls at non-towered airports.
Derivation
Mega means million, and hertz is the unit for cycles per second, named after physicist Heinrich Hertz. So 122.9 MHz means a radio signal at 122.9 million cycles per second.
Why Pilots Care
Tuning this frequency lets pilots maintain awareness of nearby traffic and coordinate safely without involving air traffic control.
Grounding Statement
Picture approaching a small airport with no tower: 122.9 MHz may be the common radio channel where pilots announce their arrival, landing, and departure intentions.
Intuition Check
Do not assume 122.9 MHz is a controller frequency just because it appears with ATC communication information. It is normally a shared pilot advisory frequency, not a frequency where a controller gives clearances.
Example Sentence 1
Ten miles south of the field, the pilot tuned 122.9 MHz and called, "Pine Hill traffic, Cessna 4-5-Tango, ten south, inbound for landing, Pine Hill."
Example Sentence 2
All traffic at the uncontrolled airport monitored 122.9 MHz and made position calls on the downwind leg.