The question raised in this forum thread touches on a persistent point of confusion within the pilot community regarding air-to-air communication frequencies, and it deserves a clear regulatory answer. In the United States, 122.75 MHz is the frequency formally designated by the FCC and recognized in the Aeronautical Information Manual for air-to-air communications between general aviation aircraft, particularly for fixed-wing, general-purpose use outside controlled airspace. Helicopters have their own designated air-to-air frequency at 123.025 MHz. By contrast, 123.45 MHz has never been officially allocated for air-to-air chatter in U.S. domestic airspace under FCC/FAA rules. Its use as an informal "party line" frequency is largely a carryover from international oceanic and remote-area operations, where ICAO guidance and regional agreements have historically tolerated or sanctioned its use for air-to-air relay when aircraft are out of VHF range of ATC or company dispatch, often over the North Atlantic, Pacific, and other oceanic tracks.
The confusion is understandable because 123.45 MHz has achieved a kind of informal global folklore status among pilots, reinforced by decades of anecdotal use, flight-sim communities, and even some foreign regulatory frameworks that do formally sanction it for air-to-air use in their airspace. However, in the U.S. domestic environment, transmitting on 123.45 outside of its narrow, sanctioned purposes can technically run afoul of FCC licensing rules, since VHF frequencies are allocated for specific purposes and unauthorized use is, in principle, subject to enforcement action. In practice, actual FCC fines for casual air-to-air chatter on 123.45 are rare to nonexistent domestically, but the correct and defensible answer for U.S. pilots wanting to talk to another aircraft without going through ATC is 122.75 MHz for fixed-wing aircraft and 123.025 MHz for helicopters. Pilots operating internationally, especially over water or in regions where 123.45 is formally designated (such as parts of Europe and other ICAO regions), will find it sanctioned and even monitored by ATC in some FIRs.
For working pilots, this matters because frequency discipline is a foundational element of safe and compliant operations, and the air-to-air frequencies are frequently used in real operational contexts: general aviation pilots coordinating position reports in non-towered traffic patterns during high-density events (like fly-ins), formation flights, glider and soaring operations relaying spacing information, and airline or business jet crews on oceanic crossings coordinating with other flights for turbulence reports, ride quality, or relay of position when HF or datalink is degraded. Airline and business jet pilots crossing the North Atlantic Track system are the most likely professional users of 123.45, and organizations like IATA have historically encouraged its use for meteorological and turbulence PIREPs when direct ATC contact isn't feasible. Knowing the distinction between domestic and international sanctioned use is operationally relevant, since misusing frequencies domestically, even without a fine, can create confusion in already congested VHF spectrum and potentially interfere with other legitimate operations nearby.
This thread also reflects a broader trend of pilots relying on online forums and informal community knowledge rather than primary regulatory sources like the AIM, FCC rules part 87, or company/FOM procedures, which can perpetuate myths or outdated practices. As spectrum congestion increases with growing GA traffic, UAS integration, and additional demands on VHF band allocations, the FAA and FCC have periodically reinforced correct frequency usage guidance, and pilots—especially those transitioning between GA, corporate, and airline operations—should treat frequency assignment as seriously as any other regulatory requirement, verifying current guidance in the AIM (paragraph 4-1-11 covers UNICOM and other frequency uses) rather than relying on anecdotal practice. For corporate and airline pilots, the safest practice is to use 122.75 domestically for any legitimate air-to-air need and reserve 123.45 for oceanic or ICAO-sanctioned contexts, consistent with company SOPs and international AIP guidance for the specific FIR being transited.