Distress, urgency and communication contingencies
The purpose of an emergency transmission is to make a safety problem understood with the appropriate priority. Distress concerns grave and imminent danger requiring immediate assistance; urgency concerns safety without that distress condition. MAYDAY and PAN PAN are therefore different priority signals, not interchangeable labels for any inconvenient event. The category depends on the actual circumstances, including threats to persons, rather than merely the name of a malfunction.
Useful emergency information
A useful message identifies the aircraft and explains the nature of the problem, intentions, position and other information needed for assistance. Time pressure and available information affect what can be transmitted. Do not invent a rule that a person must complete a long checklist before calling for help, or that every symptom always belongs to one category. Continue to use the applicable emergency procedures and clear language as the situation changes.
The frequency already in use can give access to a station familiar with the aircraft. The international emergency frequency is another important means of contact, not a reason to believe that a distress call on the working frequency is invalid. Other stations should avoid obstructing distress traffic, listen and provide assistance or relay when appropriate. The aviation phraseology used to impose or end silence must not be replaced by a maritime expression merely because both involve emergencies.
Distinguish the failed function
A communication failure can involve selection, audio equipment, a transmitter, a receiver, an antenna or the communication path. A functioning receiver with a failed transmitter is different from a functioning transmitter with failed reception. Selection and audio checks help identify the situation when appropriate, but this guide supplies no universal switch sequence or permission to reset equipment. Follow the aircraft's actual procedures and the applicable rules.
Blind transmission is a defined communication technique where reception by the other station may remain possible. It is not proof that the receiver heard the message or approved the intended action. Alternative means and transponder functions depend on what works and what the actual procedure permits. A theoretical question cannot establish a real aircraft's equipment state.
Avoid invented lost-communication routes
Route, level, timing, visual conditions and local procedures all matter to an actual communication-failure response. A slogan such as follow the flight plan does not contain the complete current rule. This bank intentionally excludes under-specified route and descent answers, obsolete code conventions and generic instructions to continue a real approach. Recognize the problem, preserve accurate communication and consult the relevant current aircraft and operational procedures.