This section describes requirements for Flight Plan Filers (FPF) and format to receive automatic acknowledgement (ACK) and/or rejection (REJ) messages for International Civil Aviation Organization (ICAO) compatible messages. Flight plans submitted in accordance with FAA Form 7233-4, International Flight Plan (PDF), or other ICAO messages, regardless of their source, will be acknowledged.

Use of Optional Elements in Field 3 (Message Type), to Identify a Filed Flight Plan (FPL)

FAA’s automation system will accept an Optional Message Number (Field 3b) in an FPL. The Optional Message Number consists of three (3) parts:

• Part 1: The three-letter NADIN address where the FPF would like the acknowledgement message sent, followed by an oblique stroke (XXX/);
• Part 2: The four-letter location identifier of the FAA Air Route Traffic Control (ARTCC) to which the FPL is addressed by the FPF (KZXX); and
• Part 3: A three-digit sequential message number assigned by the FPF (ddd).

Example: “AWE/KZHU004” is message number 004 addressed to addressed to Houston ARTCC with ACK to be sent to American West

Note: If Part 1 of the Field 3b Optional Message Number is not adapted or not filed (NADIN address “AWE” in the above example), response will be sent to the AFTN originator address.

Message numbers should be used sequentially, 001 through 999, before restarting the message numbering sequence again at 001. Do not restart the message numbering sequence based on time of day, e.g., restart at 001 at 0000Z, or there could be ambiguity when a CHG, CNL or DLA message is received if the FAA automation system is storing multiple FPLs with the same message number.

FPL Acknowledgement (ACK) Processing

• The FPL ACK message is comprised of Fields 3 (Message Type), 7 (Aircraft Identification), 13a/b (Departure Aerodrome/Time), 16a (Destination Aerodrome) and the four-letter location identifier of the ARTCC providing the ACK.
• If the FPF supplied an Optional Message Number (Field 3b) in the FPL, that will also be included in the ACK message.

A link to examples of ACK messages can be found at the end of this section.

Cancellation (CNL) Message Processing

The CNL message is made up of Fields 3 (Message Type), 7 (Aircraft Identification), 13a (Departure Aerodrome) and 16a (Destination Aerodrome). ICAO Document 4444 specifies that a CNL message contain only the airport identifiers (Fields 13a/16a), not the times (Fields 13b/16b).

• If the FPF supplied an Optional Message Number (Field 3b) in the FPL to be cancelled, an identical Optional Reference Data (Field 3c) should be included in the CNL message. If the Optional Reference Data does not match an Optional Message Number in an existing FPL, the CNL message will be rejected.
• If a CNL message is submitted without the Optional Reference Data, the FAA automation system will attempt to cancel the FPL if no ambiguity exists; however, if multiple FPLs exist which meet the criteria of that CNL message, the CNL message will be rejected.

A link to examples of CHG messages can be found at the end of this section.

Modification (CHG) Message Processing

The CHG message is made up of Fields 3 (Message Type), 7 (Aircraft Identification), 13a (Departure Aerodrome), 16a (Destination Aerodrome) and 22 (Amendment).

• Do not include Fields 13b and 16b (Time) in a CHG message.
• If the FPF supplied an Optional Message Number (Field 3b) in the FPL to be changed, identical Optional Reference Data (Field 3c) should be included in the CHG message. If the Optional Reference Data does not match an Optional Message Number in an existing FPL, the CHG message will be rejected.
• If a CHG message is submitted without the Optional Reference Data, the FAA automation system will attempt to amend that flight if no ambiguity exists; however, if multiple FPLs exist which meet the criteria of that CHG message, the CHG message will be rejected.

A link to examples of CHG messages can be found at the end of this section.

Delay (DLA) Message Processing

The DLA message is made up of Fields 3 (Message Type), 7 (Aircraft Identification), 13a/b (Departure Aerodrome/Time) and 16a (Destination Aerodrome).

• If the FPF supplied an Optional Message Number (Field 3b) in the FPL to be changed, an identical Optional Reference Data (Field 3c) should be included in the DLA message. If the Optional Reference Data does not match an Optional Message Number in an existing FPL, the DLA message will be rejected.
• If a DLA message is submitted without the Optional Reference Data, the FAA automation system will attempt to amend that flight if no ambiguity exists; however, if multiple FPLs exist which meet the criteria of that DLA message, the DLA message will be rejected.

A link to examples of DLA messages can be found at the end of this section.

Rejection (REJ) Message Processing

A REJ message has the following format, with each REJ message element described below:
REJ [Msgid] [Center] [Error Message] [CRLF] [Input Message] 

• [Msgid] –
  • Type of message being rejected: FPL, CNL, CHG, DLA or UNK (unknown – message type cannot be determined); and
  • (If the FPF supplied Field 3b) Optional Message Number;
• [Center] – Four-letter location identifier of the ARTCC generating the REJ;
• [Error Message] – Reason for the REJ (a link to an error message chart can be found at the end of this section);
• [CRLF] – Carriage Return/Line Feed; and
• [Input Message] – Text of the entire original input message that is being rejected.

Reason for a REJ Message

The REJ message generated in response to an erroneous FPL, CNL, CHG or DLA message provides feedback on the reason for the REJ. Abbreviations Used in REJ Messages to identify Field elements.

Chart outlining REJ Error Messages, Causes and their Resolution (PDF). In the chart, “[err data]” is used as a placeholder for actual erroneous data that caused the REJ. For example, “REJ AID [err data] FORMAT” might result in the actual message “REJ AID T1234567 FORMAT” (i.e., 8 character AID too long).

Examples of ACK, CNL, CHG, DLA and REJ Messages.