If you are in contact with a Tower, a Center, or an FSS when either a distress or/and urgency develops, the communication would obviously be directed to that facility. A distress message should start with the word Mayday and be repeated at least three times. (Mayday comes from the French, M＇ aides, is pronounced Mayday, and means help me.).In an urgency, the term Panpan, again repeated three times, starts the radio transmission. Distress messages have absolute priority over all others. And the word Mayday commands radio silence on the frequency in use. Urgency messages have priority over all others except distress. Panpan warns other stations not to interfere with urgency transmissions.If, as the pilot, you have not been receiving services from an ATC facility, and if time permits, the Center. Tower or FSS in whose area of responsibility you are flying, should be contacted on the appropriate frequency. By so doing, a more rapid response to your call is likely, which is another reason for listing the various en route frequencies in the preflight planning and having the list immediately available in the cockpit. Conditions might be such, though; that there is no time to search for the correct frequency, even though a list had been prepared. In that event, two other frequencies can be used: the emergency-only frequencies of 121.5 or 243.0. Both have a range - that is generally limited to line of sight. 121.5 is guarded by direction finding stations and certain military and civil aircraft, while 243.0 is guarded by military aircraft. In addition, both frequencies are guarded by military Towers, most civil Towers, FSSs, and radar facilities. Again, if time permits, the most logical facility to try to reach first is the ARTCC in whose area you are flying, but the ARTCC’s emergency frequency capability does not nor mally extend to its radar coverage limits. If the ARTCC does not respond when called on 121.5 or 243.0 address the call to the nearest Tower or FSS. Time is crucial in a distress condition, but as much of the following as possible. Preferably in the order suggested should be communicated:(1) Mayday, Mayday, Mayday or Panpan, Panpan, Panpan(2) Name of facility addressed(3) Aircraft identification and type(4) Nature of distress or urgency(5) Weather(6) Pilot＇s intentions and request(7) Present position and heading, or if lost, last known Position, time and heading since that position.(8) Altitude or flight level(9) Hours and minutes of fuel remaining(10) Any other useful information，as visible landmarks, aircraft color, emergency equip ment on board, number of people on board.(11) Activate the ELT (Emergency Locator Transmitter) if installation permits. 5.The call on emergency-only frequencies should be directly firstly to （ ） .