It is impossible to cover all the possibilities here. The declaration of an emergency by the pilot in command is an area for your operational jugement. Emergencies can be classified according to the urgency and to the degree of seriousness of the consequences.

As the pilot, you decide, but always err on the safe side. Some categories might be:

• no urgency of time but need assistance, such as being uncertain of position and unable to confirm direction to proceed but with plenty of fuel and remaining daylight;

• some urgency of time, such as uncertain of position with fuel reserves or remaining daylight less than an hour or so;

• some urgency and potential for serious consequences, such as loss of oil pressure, rough-running engine or fuel depletion that may leave insufficient fuel to reach an airfield;

• potential seriousness but not yet developed, such as some doubt about the serviceability of the aircraft or systems, or the medical condition of the pilot;

• potential seriousness but no urgency, such as loss of primary attitude indicator with eight oktas of cloud but plenty of fuel and daylight; and

• potential catastrophe and urgency, such as risk of loss of control due to reduced visibility or daylight or risk of controlled flight into terrain due to rising ground and lowering cloud base.

It is impossible to set hard-and-fast rules. If in doubt, tell someone what the potential problem is and do it earlier rather than later, when there is still plenty of time, fuel and daylight. If there is any urgency, formally declare an emergency, at least a pan-pan. If there is any risk of loss of control or injury, declare a mayday.

If an emergency arises, it is your responsibility as pilot in command to assess just how serious the emergency is (or could be) and to take appropriate safety action. Many emergencies require your immediate attention and occupy you fully for some moments, but it is advisable at the first opportune moment to tell someone. There are three degrees of emergency and, as pilot in command, you should preface your radio call with either:

• Mayday x 3 (repeated three times) for a distress call (life treating events)

• Pan-pan x 3 (repeated three times) for an urgency call (non life treating but urgent events)

• Security x 3 (repeated three times) for a safety call.

Distress Message (or Mayday Call)
Distress is the absolute top priority call. It has priority over all others, and the word mayday should force everyone else into immediate radio silence. Mayday is the anglicized spelling of the French phrase m’aidez! which means help me! When you require immediate assistance and are being threatened by grave and immediate danger, the following applies:

• the mayday distress message should be transmitted over the air-ground frequency you are presently using;

• if you are currently using a UNICOM or tower frequency and receive no response to your distress call, and if you have time, repeat the call on the area frequency as shown on the sectional chart;

• if still no response, and if time permits, change frequency to 121.5 MHz (the international emergency frequency usually monitored by airliners and some ground stations) and repeat your distress call; and

• if your aircraft is transponder-equipped, squawk code 7700 (the emergency and urgency transponder code) which, if you are in a radar environment, causes a special symbol to appear around your aircraft on the ATC radar screen and rings an alarm bell immediately alerting the ATC radar controllers.

Urgency Message (or Pan-Pan Call)
The urgency or pan-pan message is made over the frequency in use when an emergency exists that does not require immediate assistance. Typical situations when a panpan message is appropriate include the following:

• experiencing navigational difficulties that require the assistance of ATC or flight service;

• carrying a passenger on board that has become seriously ill and requires urgent attention;

• seeing another air plane or a ship whose safety is threatened and urgent action is perhaps needed; and

• making an emergency change of level in controlled airspace that may conflict with traffic below.

There are few occasions when it would be necessary to transmit a security call. It is nonetheless useful to know of the existence of this type of message in the event that it becomes necessary to transmit one.

Procedure word

Some words with specialised meanings are used in radio communication throughout the English-speaking world, and in international radio communication, where English is the lingua franca. Note that the following list commingles incompatible terms used in different communication modes, each of which has its own terminology (e.g., no air-to-ground controller would ever use the term "10-4", a CB radio term).

 

10-4 — Message received; I understand; ok; all right

 

Affirmative / Affirm — Yes.

 

Break — Signals a pause during a long transmission to open the channel for other transmissions, especially for allowing any potential emergency traffic to get through.

 

Break-Break — Signals to all listeners on the frequency, the message to follow is priority. Almost always reserved for emergency traffic or in NATO forces, an urgent 9 line or Frag-O. In Aviation, it signifies the end of a transmission to one call-sign and the commencement of transmission to another, e.g., "G-WXYZ Standby. Break-Break. G-ABCD Cleared to Land Runway 17" etc.

 

Callsign-Actual/Callsign-Niner — Sometimes an individual (generally a superior) may have a person monitor the network for them. Saying "actual" after their callsign asserts you wish to speak to the specific person the callsign is attached to. ex: calling the callsign "Headquarters" would often get junior clerk or similar. Calling (or identifying yourself as) "Headquarters-Actual" would indicate that the commander of the headquarters detachment, and thus the entire unit to which it is attached, is requested to be spoken to, or is actually speaking. (In Canadian use, this is Callsign-Niner, with "9" designating a unit commander. An individual monitoring the net but is not the actual commander may use the call-sign "Niner-Zulu". As well, the codeword "Sunray" is also used to designate a unit commander.)

 

Come in — You may begin speaking now

 

Copy (U.S.) — I heard what you just said; ok; all right.

 

Falcon — prefix followed by a (usually three-digit) code number for an Army creole phrase.

 

Go ahead or Send your traffic — Send your transmission.

 

Mayday — Maritime/aviation distress call. Repeated three times and at beginning of every following transmission relating to the current distress situation. Has priority over urgency and safety calls.

 

Negative — No

 

Out — I have finished talking to you and do not expect a reply.

 

Over — I have finished talking and I am listening for your reply. Short for "Over to you."

 

Pan-pan — Maritime/aviation urgency call. Repeated three times. Has priority over safety calls.

 

Reading you Five / Loud and clear / Your signal is clear; 5×5.

 

Ready to Copy — Write down (e.g., "Prepare to copy" - I am going to give you detailed instructions, have something ready to write them down with; or 'I am ready to write down' when used in a reply transmission).

 

Roger — "I have received all of the last transmission" in both military and civilian aviation radio communications. This usage comes from the initial R of received: R was called Roger in the radio alphabets or spelling alphabets in use by the armed forces at the time of the invention of the radio, such as the Joint Army/Navy Phonetic Alphabet and RAF phonetic alphabet. It is also often shortened in writing to "rgr". The word Romeo is used for "R", rather than "Roger" in the modern international NATO phonetic alphabet.

Contrary to popular belief, Roger does not mean or imply both "received" and "I will comply." That distinction goes to the contraction wilco (from, "will comply"), which is used exclusively if the speaker intends to say "received and will comply". The phrase "Roger Wilco" is procedurally incorrect, as it is redundant with respect to the intent to say "received".

 

Roger So Far — Confirm you have received and understood the contents of my transmission so far. This is used during Long Message Procedure (Messages lasting over 20 seconds prefixed by the Pro-Word 'Long Message' and the initiating C/S must give a gap of five seconds after the receiving station has replied with 'Roger'. This five seconds is to allow other Stations onto the net if they have important messages.

Say again repeat; Please repeat your last message (Repeat is only used in Australian/Canadian/UK/US military radio terminology to request additional artillery fire)

 

Sécurité — Maritime safety call. Repeated three times. Has priority over routine calls.

Standby or Wait, out — Pause for the next transmission. This does not usually entail staying off the air until the operator returns as they have used the word 'Out', which indicates the transmission has ended. The net is now free for other traffic to flow but users should be aware that the previous C/S may re-initiate a Call as per their 'Wait, out'. As with 'Wait', this can be appended with a number to indicate estimated number of minutes. For example: "We are on the phone with them trying to sort this out, standby five."

 

Wait, over — I do not have the answer or information to hand, I will attempt to source the answer or information requested shortly but until then I have finished talking and do not expect a reply. Can be suffixed with a number to indicate estimated number of minutes until a reply can be expected. ex: WAIT TWO indicates "you should expect my reply in approximately two minutes."

 

Wilco — Will comply (after receiving new directions, implies Roger).

 

Niner — Used by CSX to mean "nine/9" during radio transmissions, especially by talking lineside defect detectors. It is used to avoid confusion with five, as the two numbers can easily be mixed up when there is a lot of static. The German word for no is also "nein" (pronunciation: /naɪn/) and would cause confusion with the number 9.

Each area of usage will have its own subset of prowords, usually derived from the NATO set, but sometimes from earlier Q-code and morse operator practices.

Furthermore, the use of some special prowords is tightly controlled, with that word never used on the air in other contexts within that area of usage. Examples include "repeat" (for additional artillery fire in military communications), "take off" (granting permission for aircraft take off in airfield tower communications), "rescue" (rescue in progress in surf life saving), and "mayday" (safety-of-life emergency in maritime and aeronautics).

Other urgent calls

 

Pan-pan

Pan-pan (from the French: panne—a breakdown) indicates an urgent situation of a lower order than a "grave and imminent threat requiring immediate assistance", such as a mechanical breakdown or a medical problem. The suffix medico used to be added by vessels in UK waters to indicate a medical problem (Pan-pan medico, repeated three times), or by aircraft declaring a non-life-threatening medical emergency of a passenger in flight, or those operating as protected medical transport in accordance with the Geneva Conventions. "Pan-pan medico" is no longer in official use.

 

Declaring emergency

Sometimes the phrase "declaring emergency" is used in aviation. This is the same as calling "Mayday". For example, Swissair Flight 111 radioed "Swissair one eleven heavy is declaring emergency" on discovering their situation.

However, ICAO recommends the use of the standard "Pan-pan" and "Mayday" calls instead of "declaring an emergency". Cases of pilots using phrases other than "Pan-pan" and "Mayday" have caused confusion and errors in aircraft handling.

 

Sécurité

Sécurité (/seɪˈkjʊərᵻteɪ/; from French sécurité—safety) indicates a message about safety, such as a hazard to navigation or weather information.

 

Silence

The following calls may be made only by the vessel in distress or the responding authority:

Seelonce Mayday or Seelonce Distress means that the channel may only be used by the vessel in distress and the Coast Guard (and any other vessels they ask to assist in handling the emergency). The channel may not be used for normal working traffic until "seelonce feenee" is broadcast.

"SEELONCE MAYDAY" (followed by the name of the disturbing station) may only be sent from the vessel in distress. "SEELONCE DESTRESSE" (followed by the name of the disturbing station) may only be sent from a station which is not participating on the emergency traffic.

The expressions Stop Transmitting—Distress and Stop Transmitting—Mayday are the aeronautical equivalents of Seelonce Mayday.

Seelonce Feenee (French: silence fini—silence finished) means that the emergency situation has been concluded and the channel may now be used normally. The word prudonce (prudence—"caution") can also be used to allow restricted working to resume on that channel.

Distress Traffic Ended is the aeronautical equivalent of seelonce feenee.