What is the correct way to communicate the frequency being used by an aircraft?

The most appropriate way to communicate the frequency being used by an aircraft is to state "On frequency 118.67." This phrasing is standard in aviation communication and indicates that the aircraft is currently tuned to that specific frequency. The use of "on" implies active engagement with the frequency, which is essential for clarity and effective communication among pilots and air traffic control.

The other options, while they might convey a similar message, do not align with standard aviation communication protocols. Using "using frequency 118.67" could imply that the frequency is merely available, not that the aircraft is actively listening or transmitting on it. "At frequency 118.67" suggests a location rather than direct communication, which may lead to confusion about the aircraft's current operations. "With frequency 118.67" is less common and does not convey the same level of immediacy regarding the aircraft's communication status. Therefore, the phrasing of "On frequency 118.67" is the clearest and most recognized form in aviation communication.