Aeronautical Communication Associated Terms and Message Priorities
Categories of Messages
According to ICAO Annex 10, Volume II, the messages handled by the aeronautical mobile service are classified by priority. The order of priority for establishing communications and transmitting messages is as follows:
- Distress (Signal: MAYDAY): Distress calls, messages, and traffic.
- Urgency (Signal: PAN PAN): Urgency messages, including those preceded by the medical transports signal.
- Direction Finding: Communications relating to direction finding.
- Flight Safety: Messages concerning movement and control (ATC instructions), messages of immediate concern to an aircraft in flight, and important meteorological advice.
- Meteorological: Meteorological messages.
- Flight Regularity: Messages regarding the operation or maintenance of facilities, or company messages (e.g., schedule changes, fuel requests).
Communication Methods
There are distinct ways to classify communication channels:
- Simplex: A method in which telecommunication between two stations takes place in one direction at a time.
- Examples include standard ATC communications where you push-to-talk.
- Duplex: A method in which telecommunication between two stations can take place in both directions simultaneously.
- Example: Telephone conversation.
It is also important to distinguish between air-ground relationships:
- Air-ground communication: Two-way communication between aircraft and stations or locations on the surface of the Earth.
- Ground-to-air communication: One-way communication from stations or locations on the surface of the Earth to aircraft (e.g., ATIS, VOLMET).
Q-Codes (Navigation)
A specific set of Q-codes is used to describe bearings and headings.
| Code | Definition | Description |
|---|---|---|
| QDM | Magnetic heading TO the station | Magnetic bearing to the station (zero wind). |
| QDR | Magnetic bearing FROM the station | The magnetic radial you are currently on. |
| QUJ | True heading TO the station | True bearing to the station. |
| QTE | True bearing FROM the station | The true bearing from the station to the aircraft. |
| QNH | Altimeter setting | Atmospheric pressure adusted to Mean Sea Level (MSL). |
| QFE | Altimeter setting | Atmospheric pressure at aerodrome elevation (or runway threshold). |
Service Availability Codes
These abbreviations indicate the operational hours of a service (e.g., in NOTAMs or AIP):
- H24: Continuous day and night service.
- HJ: Sunrise to sunset (Day schedule).
- HN: Sunset to sunrise (Night schedule).
- HS: Service available during hours of scheduled operations.
- HX: No specific working hours.
Key Definitions
- CAVOK (Ceiling And Visibility OK): Used when visibility is 10 km or more, there are no clouds of operational significance (no clouds below 5000 ft or MSA, no CB/TCU), and no significant weather.
- AIS (Aeronautical Information Service): Ensures the flow of information/data necessary for the safety, regularity, and efficiency of international air navigation.
- AFIS (Aerodrome Flight Information Service): Provides information and instructions to aircraft at non-controlled aerodromes to assist in safe operations.
- RNAV (Area Navigation): A navigation method allowing flight on any desired path within the coverage of station-referenced aids or within the limits of self-contained aids, rather than flying strictly "to" or "from" ground stations.
- Clearance Limit: The point to which an aircraft is granted an air traffic control clearance.
- Expected Approach Time (EAT): The time ATC expects an arriving aircraft, following a delay, will leave the holding fix to complete its approach.
- Visual Approach: An approach by an IFR flight when either part or all of an instrument approach procedure is not completed and the approach is executed in visual reference to terrain.
Instrument Approach Types
- Non-Precision Approach (NPA): A 2D instrument approach (lateral guidance only).
- Approach with Vertical Guidance (APV): A PBN instrument approach with vertical guidance (3D) that does not meet precision approach standards (e.g., LPV).
- Precision Approach (PA): A 3D instrument approach based on systems like ILS, MLS, or GLS.