If not published, what frequency should be used for aerodrome traffic?

The use of 123.2 MHz for aerodrome traffic is widely accepted as a common practice in aviation. This frequency is designated for non-towered aerodromes, where a formal air traffic control tower is not present to manage the air traffic. In such environments, it is essential for pilots to communicate their intentions to ensure safety and coordination among all aircraft in the vicinity. Since this frequency is commonly used but not necessarily published, it provides a reliable means for pilots to announce their positions and intentions, which helps prevent potential conflicts during takeoffs, landings, and taxi maneuvers.

In contrast, the other frequencies listed are either specifically designated for different purposes or are not standard for aerodrome traffic. For instance, 121.5 MHz is internationally recognized as the emergency frequency, and is reserved for distress signals, so it's not appropriate for aerodrome traffic communications. Frequencies like 125.0 MHz and 130.0 MHz are sometimes used in specific regions or for specific types of operations, but they do not hold the same universal acceptance as 123.2 MHz for aerodrome communication. Thus, the choice of 123.2 MHz serves to enhance safety and situational awareness at non-towered airports.