User:Johan G/Standard ICAO ATS messages and fields

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Caution  Not for real life use While this is a rather comprehensive write-up, and some care have been taken to make it as correct and current as possible, errors and omissions are inevitable.
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To help organise the flow of air traffic, air traffic service messages, (ATS messages) are sent within and between the air traffic service (ATS) organisations, such as aerodrome control towers, approach/departure control and area control centres (ACC). The following messages and the fields they are composed of are standardised by ICAO and are used for most internal flights, and probably in many flight information regions for domestic flights. Regional differences do occur with both omissions and additions.

One of the more commonly known messages is the larger part of the initial flightplan (the filed flight plan message, which include all the items of the ICAO flight plan form except item 19, Supplementary information).

Summary of ATS messages and fields

Message category Message type Message type

designator

Fields
3 5 7 8 9 10 13 14 15 16 17 18 19 20 21 22
Emergency

messages

Alerting ALR 3 5 7 A 8 9 A 10 13 A 15 A 16 A 18 A 19 A 20 A
Radio communication failure RCF 3 7 13 16 21 A
Movement

messages

Filed flight plan FPL 3 7 8 9 A 10 13 A 15 A 16 A 18 A
Delay DLA 3 7 13 16 18
Modification CHG 3 7 13 16 18 22 B
Flight plan cancellation CNL 3 7 13 16 18
Departure DEP 3 7 13 16 18
Arrival ARR 3 7 13 16 17
Coordination

messages

Current flight plan CPL 3 7 8 9 A 10 13 A 14 15 A 16 A 18 A
Estimate EST 3 7 13 14 16
Coordination CDN 3 7 13 16 22 B
Acceptance ACP 3 7 13 16
Logical acknowledgement LAM 3
Supplementary

messages

Request flight plan RQP 3 7 13 16 18
Request supplementary flight plan RQS 3 7 13 16 28
Supplementary flight plan SPL 3 7 13 16 A 18 A 19 A

Notes: A. These fields will begin a new line when printed in teleprinter page form; B. This field type can be repeated if needed.

Conventions

Character set

The ATS messages uses a very limited character set. The reason is that it has to be compatible with the International Telegraph Alphabet No. 2 (ITA2) used with teletypewriters.

Characters used are:

  • Character, which can be either of
    • Letter, upper case, A-Z
    • Digit, 0-9
  • Special character:
    • Parenthesis, left and right ( and )
    • Hyphen -
    • Forward slash /
    • Plus sign +
    • Space
    • Carriage return
    • Line feed

Composition of messages

The messages begins with a left parenthesis ( and ends with a right parenthesis ). Each field begins with a single hyphen - and contains one or more elements. The fields contains characters consisting of upper case letters, decimal digits and in some cases single spaces as separators between elements and single and forward slashes as separators between elements and/or to indicate that certain kinds of data will follow.

For some reasons the fields are mentioned as items when used in the context of filling in flight plan forms and filing them, but as field types when used in the context of contents and sending of messages.

Time convention

Time is given as UTC time in 24 hour format without colon. 22:35 would be given as 2235.

Position and route conventions

The position can be given in four ways:

  • 2-5 characters giving an en-route pint (fix) designation, for example HADLY
  • 4 digits, giving the latitude in degrees and minutes, followed by either N or S, followed by 5 digits giving the longitude in degrees and minutes, followed by either E or W, for example 3724N12235E
  • 2 digits, giving the latitude in degrees, followed by either N or S, followed by 3 digits giving the longitude in degrees, followed by either E or W, for example 37N123E
  • 3-5 characters giving a specific point designation, followed by 3 digits giving a magnetic bearing from the point, followed by 3 digits giving a distance in nautical miles from the point, for example OAK204025. In areas of high latitude true bearing may be used instead.

Routes can be given as below:

  • 2-7 characters giving an ATS route designation, for example V27

Level conventions

Levels/altitudes can be given in four ways indicated by a preceding upper case letter:

  • F followed by 3 digits indicates a flight level. FL330 would be given as F330.
  • S followed by 4 digits indicates standard metric level in tens of metres. Standard metric level 11,300 metres would be given as S1130.
  • A followed by 3 digits indicates altitude in hundreds of feet. 4,500 feet would be given as A045.
  • M followed by 4 digits indicates altitude in tens of metres. 8,400 metres would be given as M0840.

Airspeed conventions

The true airspeed can be given in 3 ways:

  • K followed by 4 digits giving the true airspeed in kilometres per hour, for example K0630 for 630 km/h
  • N followed by 4 digits giving the true airspeed in knots, for example N0340 for 340 kt
  • M followed by 3 digits giving the true airspeed in Mach to the nearest hundreds, if prescribed by ATS authority, for example M0550 for M 0.550

Addressing of messages in areas with automated systems

In areas where automated systems are used for exchange of flightplan data between several area control centres, approach and departure control and aerodrome control towers, the messages are not sent to each individual ATS service, but to these automated services.

Message types and their use

Alerting (ALR) messages

If the ATS unit believes that an aircraft is any of the following phases of emergency, an alerting message should be sent to any ATS and rescue coordination units related to the flight.

If there is an agreement between ATS units to do so the alerting message can instead be sent as an modification (CNG) or coordination (CDN) message supplemented with verbal messages giving the additional details.

The phases of emergency are:

  • Uncertainty phase if:
    • The aircraft have not tried to make a planned communication after 30 minutes
    • The aircraft have not answered to radio calls following a time for a planned communication
    • The aircraft is more than 30 minutes over due to arrival
  • Alert phase if:
    • Further attempts to establish communication fails
    • No more news about the aircraft can be gathered
    • An aircraft are more than 5 minutes late to estimated landing after a landing clearance and communication can not be established
    • The aircraft's performance have been impaired, but not enough to force a landing
    • When an aircraft is believed to have been hijacked
  • Distress phase if:
    • Further communication attempts fail
    • The fuel is estimated to have been exhausted or insufficient to reach an aerodrome
    • The aircraft's performance is impaired enough to force a landing
    • The aircraft are known to have made a forced landing

Radio communication failure (RCF) messages

If an ATS unit is aware that an aircraft has a radio communication failure a radio communication failure (RCF) message shall be sent to the ATS units along the continued flight that have received a filed flight plan (FPL) message as well as to the destination aerodrome.

If the subsequent ATS unit have not received a flight plan due to used procedures the radio communication failure (RCF) message shall be accompanied by a current flightplan (CPL) message, which that ATS unit will forward to the other ATS units and to the destination aerodrome.

Filed flight plan (FPL) messages

Delay (DLA) messages

If a flights estimated start of taxing (EOBT, estimated off-block time) will be delayed more than 30 minutes and a filed flight plan (FPL) have been sent a delay (DLA) message shall be sent to the departure aerodrome ATS and to all ATS units that have received a filed flight plan (FPL) message.

Modification (CHG) messages

If any change is made to the flight plan, a modification (CNG) message shall be sent to all affected ATS units that have received a filed flight plan (FPL) message.

Flight plan cancellation (CNL) messages

When a flight is cancelled for which a filed flight plan message have been sent the ATS unit at the departure aerodrome will send a flight plan cancellation (CNL) message to all ATS units that have received the filed flight plan (FPL) message.

Departure (DEP) messages

Immediately after departure the ATS unit at the departure aerodrome shall send a departure (DEP) message to all other ATS units that have received the filed flight plan (FPL) message, unless agreed otherwise.

Arrival (ARR) messages

When an arrival is reported to the ATS unit serving the arrival aerodrome that unit shall transmit an arrival (ARR) message:

  • If the flight landed at the destination aerodrome:
    • To the area control centre (ACC) or flight information centre in the area of the aerodrome, if required by that unit.
    • To the ATS unit of the departure aerodrome which originated the flight plan message, if that message included a request for an ARR message.
  • If the flight landed at an alternate or other aerodrome:
    • To the area control centre (ACC) or flight information centre in the area of the arrival aerodrome
    • To the control tower at the destination aerodrome
    • To the air traffic reporting services of the departure aerodrome
    • To each ACC or flight information centre in charge of each FIR or upper FIR the flight would have passed if it had not diverted.

When a flight which have had a loss of two-way communications have landed the arrival aerodromes control tower shall transmit an arrival (ARR) message:

  • If the flight landed at the destination aerodrome:
    • To all ATS units involved in the flight during the communication failure.
    • To all other ATS units that might have been alerted.
  • If the flight landed at an alternate or other aerodrome:
    • To the ATS unit serving the destination aerodrome, which shall then transmit an arrival (ARR) message as above.

Current flight plan (CPL) messages

If a flight plan (FPL) message which will be complemented by estimate (EST) messages have not been sent, a current flight plan (CPL) message shall be transmitted from one ACC to the next and finally to the control tower of the destination aerodrome. This shall be done for all flights under air traffic advisory service along the routes or portion of routes that have been determined to have suitable conditions for point to point communications.

The current flight plan (CPL) message shall only contain data relevant from the point where it enters the next control area.

Whether or not the an ATS unit has had contact with an aircraft, except if there is another time period prescribed, it shall transmit a current flight plan (CPL) message early enough that the receiving ATS unit will receive it at least 20 minutes before it is estimated that the aircraft will pass the boundary between the ATS units.

Estimate (EST) messages

When basic flight plan data has been transmitted, an estimate (EST) message shall be transmitted by each area control centre or flight information centre to the next area control centre or flight information centre along the route.

Whether or not the an ATS unit has had contact with an aircraft, except if there is another time period prescribed, it shall transmit a estimate (EST) message early enough that the receiving ATS unit will receive it at least 20 minutes before it is estimated that the aircraft will pass the boundary between the ATS units.

Coordination (CDN) messages

If a transmitting or a receiving ATS unit wants to propose a change in the data of a preceding current flight plan (CPL) or estimate (EST) message, a dialogue with coordination (CDN) messages may start and continue until one of the ATS units transmit an acceptance (ACP) message. Normally the issue is resolved using voice communication. This process can be repeated if needed.

Acceptance (ACP) messages

Unless special arrangements have been made between ATS units, an acceptance (ACP) message is transmitted by an accepting ATS unit when a current flight plan (CPL) or estimate (EST) message have been accepted. See also coordination (CDN) messages above.

Logical acknowledgement (LAM) messages

Logical acknowledgement (LAM) messages are only used between ATC computers, which will transmit them when a message have been received and processed to the point that the data is available to the ATC controller.

When a current flight plan (CPL) or estimate (EST) message is transmitted, the transmitting ATC computer should wait for the logical acknowledgement (LAM) message, and should show a warning if it is not received, whereupon systems like vice communications and and manual operation may be used as a backup.

Request flight plan (RQP) messages

Request supplementary flight plan (RQS) messages

Supplementary flight plan (SPL) messages

Message field types

Field type 3 - Message type, number and reference data

(ESTA/B003

Element b are only used in a few message types.

Element a - Message type

  • 3 letters

Element b - Message number

  • Sending unit, 1-4 letters
  • Forward slash
  • Receiving unit, 1-4 letters
  • Message number from the sender to the receiver, 3 digits

Field type 5 - Description of emergency

–ALERFA/EINNZQZX/REPORT OVERDUE

Element a - Phase of emergency

  • Depending on the declared phase of the emergency:
    • INCERFA, for an uncertainty phase
    • ALERFA, for an alert phase
    • DETRESFA, for a distress phase

Element b - Originator of message

  • Forward slash
  • 8 letters, of which:
    • 4 letters gives the ICAO location designator
    • 3 letters gives the originating ATS unit
    • X, or if applicable, 1 letter designating the division of the originating ATS unit

Element c - Nature of emergency

  • Forward slash
  • Short plain language description of the emergency

Field type 7 - Aircraft identification, SSR mode and SSR code

–UAL219/A5300

In messages where the transponder code is not known or is irrelevant elements b and c are not used.

Element a - Aircraft identification

  • 2-7 characters

Element b - Transponder mode

  • Forward slash
  • Letter A

Element c - Transponder code

  • 4 digits 0-7 (octal numbers)

Field type 8 - Flight rules and type of flight

–IS

Element a - Flight rules

  • Either of:
    • I, for flights that will be under instrument flight rules
    • V, for flights that will be under visual flight rules
    • Y, for flights that will begin under instrument flight rules
    • Z, for flights that will begin under visual flight rules

If Y or Z is used, the points at which the flight rules used change should be indicated in field type 15.

Element b - Type of flight

  • Either of:
    • S, for scheduled flights
    • N, for non-scheduled air transports
    • G, for general aviation flights
    • M, for military flights
    • X, for other types of flight

Field type 9 - Number and type of aircraft and wake turbulence category

–3DC3/M

Element a are only used if there are more than one aircraft.

Element a - Number of aircraft

  • 1-2 digits

Element b - Type of aircraft

  • 1 letter and 1-3 characters

Unless found in ICAO DOC 8643 - Aircraft Type Designators (see below), element b should, be ZZZZ and the type should be added to field type 18 after a /TYP tag.

Element c - Wake turbulence category

  • Either of:
    • L, light, for aircraft with a certified MTOW below 7,000 kg (15,500 lb)
    • M, medium, for aircraft with a certified MTOW between 7,000 kg and 136,000 kg (300,000 lb)
    • H, heavy, for aircraft with a certified MTOW above 136,000 kg

In some areas J, jumbo or super, are used for the Airbus A380-800.

The wake turbulence category (WTC) can be found in ICAO DOC 8643 - Aircraft Type Designators.

Field type 10 - Equipment and capabilities

Element a - Communication and navigation equipment and capabilities

Element b - Surveillance equipment and capabilities

Field type 13 - Departure aerodrome and time

-AFIL2240

Element a - Departure aerodrome

  • 4 letters

If the departure was not from an aerodrome with a designation, or from an unknown location ZZZZ should be used and the name and location should be given in field type 18 if that field type is a part of the message.

If a flight plan is filed while in the air AFIL should be used and the flight control unit from which more information could be given should be shown in field type 18 if that field type is a part of the message.

Element b - Departure time

  • 4 digits

UTC time in 24 hour format.

For FPL, ARR, CHG, CNL, DLA, RQS, RQP messages, the estimated off-block time (EOBT) at the aerodrome if known.

ALR, DEP and SPL, the actual time of departure from the aerodrome.

For FPL messages derived from flight plans filed in the air shown by AFIL, the actual or estimated time of departure from the first point shown in field type 15.

Field type 14 - Estimate data

 –CLN/1831F240F180A

If the aircraft will be passing the boundary point in level flight, elements d and e will be omitted.

Element a - Boundary point

Element b - Time at boundary point

  • Forward slash
  • 4 digits giving the estimated UTC time the aircraft will pass the boundary point

Element c - Cleared level

  • The cleared level of the aircraft in level flight or if passing the boundary point in a climb or descent the cleared level after the climb or descend

Element d - Supplementary crossing data

  • An estimated level at which the aircraft will pass the boundary point, or a level the aircraft will pass above or below according to element e

Element e - Crossing condition

Either of:

  • A if the aircraft will pass the boundary point at or above the level given in element d
  • B if the aircraft will pass the boundary point at or below the level given in element d

Field type 15 - Route

–N0420F310 R10 UB19 CGC UA25 DIN/N0420F330 UR14 IBY UR1 MID

This field does not contain the departure or destination aerodrome as those are given in field types 13 and 16.

Element c can be added as many times as necessary. If the message has been transmitted before the field can be truncated using element c5 and the T indicator.

Elements c1 and c2 may only be followed by c3 and c4.

Elements c1 and c7 only needs to be added where necessary.

Elemnt c5 may only be followed by elements c3, c4 and c6.

In some regions a non-standard stay element is used for activities like photographic missions, flight training, etc. The stay shall be complemented with a stayinfo element in field type 18 describing the activity during the stay.

Element a - Cruising speed or Mach number

Element b - Requested cruising level

Element c1 - Standard departure route

  • Space
  • Designator for the standard departure route from the aerodrome to the first significant point (fix) on the route as per Position and route conventions

Element c2 - ATS route designator

Element c3 - Significant point

Element c4 - Significant point/cruising speed and cruising level

Element c5 - Indicator

  • Space
  • Either:
    • IFR if a change to instrument flight rules will be made after the previous point
    • VFR if a change to visual flight rules will be made after the previous point
    • DCT if the flight to the next point will be outside the route, unless both points are given as geographical coordinates or a bearing and distance from a point
    • T if the route is truncated after the previous point and the route can be found in a previously transmitted message. If shown this element must end the field.

Element c6 - Cruise climb

  • Space
  • C/
  • Significant point where the cruise climb will start given as per Position and route conventions
  • /
  • Climbing speed or Mach number as per Airspeed conventions
  • Either of:
    • Two levels:
      • The level at the beginning of the climb given as per Level conventions
      • The level at the end of the climb given as per above
    • Only one level:
      • The level at the beginning of the climb given as per above
      • +

Element c7 - Standard arrival route

  • Space
  • Designator for the standard arrival route to the aerodrome from the last significant point (fix) on the route as per Position and route conventions

Stay element

  • STAY
  • Digits as needed giving the sequential number of the stay in the route
  • /
  • 4 digits giving the estimated time at the stay in hours and minutes

Field type 16 - Destination aerodrome, total estimated elapsed time and alternate aerodrome(s)

–EHAM0645 EBBR EDDL

Element b and c are only used in message types ALR, FPL and SPL.

Element c may not be used depending on regional agreements.

Element c may be used 2 times separated by space.

Element a - Destination aerodrome

  • 4 letters giving the destination aerodrome identifier.

If the airport does not have an identifier, ZZZZ should be used and the name and location should be given in field type 18 if that field type is part of the message.

Element b - Total estimated elapsed time

  • 4 digits giving the total estimated elapsed time

Element c - Destination alternate aerodrome(s)

  • Space
  • 4 letters giving the alternate destination airport identifier.

If the airport does not have an identifier, ZZZZ should be used and the name and location should be given in field type 18 if that field type is part of the message.

Field type 17 - Arrival aerodrome and time

–ZZZZ1620 DEN HELDER

Element c is unly used if the aerodrome does not have a four letter designation.

Element a - Arrival aerodrome

  • 4 letters giving the destination aerodrome identifier.

If the airport does not have an identifier, ZZZZ should be used and the name should be given in element c.

Element b - Arrival time

  • 4 digits giving the total estimated elapsed time

Element c - Name of arrival aerodrome

  • Space
  • Name of the aerodrome

Field type 18 - Other information

–STS/MEDEVAC
  • 0 (zero) if this field does not contain any information

or, as needed, the following designators in sequential order and separated by spaces:

  • STS/ indicating that reasons for special handling by the ATS service followed by one or more of the below indicators in sequential order and separated by spaces
    • ALTRV for a flight with an altitude reservation
    • ATFMX for a flight approved for exemption from flow management measures
    • FFR for a fire-fighting flight
    • FLTCK for a flight check flight for calibration of navigation aids
    • HAZMAT for a flight carrying hazardous materials
    • HEAD for a flight carrying a head of state
    • HOSP for a medical flight
    • HUM for a humanitarian flight
    • MARSA for a flight for which a military entity assumes responsibility for separation of military aircraft
    • MEDEVAC for a medical emergency evacuation flight
    • NONRVSM for a flight in reduced vertical separation minima (RVSM) airspace with an aircraft without required equipment
    • SAR for a search and rescue flight
    • STATE for a military, customs or police services flight

Other reasons for special handling by ATS should be included after a RMK/ indicator.

  • PBN/
  • NAV/
  • COM/
  • DAT/
  • SUR/
  • DEP/
  • DEST/
  • DOF/
  • REG/
  • EET/
  • SEL/
  • TYP/
  • CODE/
  • DLE/
  • OPR/
  • ORGN/
  • PER/
  • ALTN/
  • RALT/
  • TALT/
  • RIF/
  • RMK/

Field type 19 - Supplementary information

–E/0745 P/6 R/VE S/M J/L D/2 8 C YELLOW A/YELLOW RED TAIL N145E C/SMITH

Element a - Fuel endurance

  • E/
  • 4 digits giving the fuel endurance in hours and minutes

Element b - Persons on board

  • Space
  • P/
  • 1-3 digits giving the number of persons on board when prescribed by ATS authority

Element c - Radio equipment

  • Space
  • R/
  • One or more of the following without spaces:
    • U giving that UHF emergency radios 243.0 MHz are available
    • V giving that VHF emergency radios 121.5 MHz are available
    • E giving that emergency locator transmitters (ELTs) are available


Element d - Survival equipment

  • Space
  • S/
  • One or more of the following without spaces:
    • P giving that polar survival equipment is available
    • D giving that desert survival equipment is available
    • M giving that maritime survival equipment is available
    • J giving that jungle survival equipment is available

Element e - Life jackets

  • Space
  • J/
  • One or more of the following without spaces:
    • L giving that live jackets equipped with lights
    • F giving that live jackets equipped equipped with fluorescents
    • U giving that live jackets equipped with UHF 243.0 MHz radios
    • V giving that live jackets equipped with VHF 121.5 MHz radios

Element f - Dinghies

  • Space
  • D/
  • One or more of the following separated by spaces:
    • 1-2 digits giving the number of dinghies carried
    • 1-3 digits giving the capacity of all the dinghies combined
    • C if the dinghies are covered
    • The colour of the dinghies

Element g - Aircraft visual characteristics

  • Space
  • A/
  • One or more of the following separated by spaces:
    • The colour of the aircraft
    • Significant markings which could include the registration

Element h - Other survival equipment and remarks

  • Space
  • N/
  • Any other survival equipment and any useful remarks

Element i - Pilot in command

  • Space
  • C/
  • The name of the pilot in command

Field type 20 - Alerting search and rescue information

–USAF LGGGZAZX 1022 126.7 GN 1022 PILOT REPORT OVER NDB ATS UNITS ATHENS FIR ALERTED NIL

Unknown or unavailable information should be shown as NIL or NOT KNOWN instead of being omitted.

The field are composed of the following elements separated by spaces.

Element a - Identity of operator

  • 2 letters giving ICAO operator aircraft designation or if unassigned the name of the operator

Element b - Unit which made last contact

  • 6 letters, of which:
    • 4 letters giving an ICAO location indicator
    • 2 letters giving the designation of the ATS unit which had the last two-way radio contact with the aircraft

If those are not available, some other description of the unit

Element c - Time of last two-way contact

  • 4 digits giving the UTC time of the last two-way radio contact in hours and minutes

Element d - Frequency of last contact

  • Digits as necessary to give the radio frequency of the last contact

Element e - Last reported position

Element f - Method of determining last known position

  • Description in plain language as necessary

Element g - Action taken by reporting unit

  • Description in plain language as necessary

Element h - Other pertinent information

  • Description in plain language as necessary

Field type 21 - Radio failure information

–1232 121.3 CLA 1229 TRANSMITTING ONLY 126.7 LAST POSITION CONFIRMED BY RADAR

Unknown or unavailable information should be shown as NIL or NOT KNOWN instead of being omitted.

The field are composed of the following elements separated by spaces.

Element a - Time of last two-way contact

  • 4 digits giving the UTC time of the last two-way radio contact in hours and minutes

Element b - Frequency of last contact

  • Digits as necessary to give the radio frequency of the last contact

Element c - Last reported position

Element d - Time at last reported position

  • 4 digits giving the UTC time of the last two-way radio contact in hours and minutes

Element e - Remaining COM capability

  • Remaining communication capability, if known, either using the convention in field type 10, or in plain language

Element f - Any necessary remarks

  • Plain language s necessary

Field type 22 - Amendment

–8/IN

This field can be used more than once if necessary.

Element a - Field indicator

  • 1-2 digits giving the number of the field type to be amended

Element b - Amended data

  • Complete and amended contents of the field to be amended, as per specification above

External links

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