A6) Use of Item 18 in ATS messages

Assigned To


Issue Status



(2) Normal


A-6) The changes contained in Appendix 3, Air Traffic Service Messages, now require that Item 18 (Other Information) must now be included in CHG, CNL, DLA, DEP and RQS messages. Although it appears this change is necessitated by the new allowance of FPL filing up to 120 hours in advance which requires inclusion of DOF/ in Item 18, the Amendment 1 to the PANS ATM has the effect of requiring that the entire Item 18 be routinely included in CHG, CNL, DLA, DEP and RQS messages. Item 18 is a very lengthy field, so the change has the consequence of vastly increasing the size of ATS messages being sent over AFTN networks and greatly increasing associated message storing and processing functions in ANSP systems which handle these messages.
 The example CHG message shown at paragraph includes a DOF/ change, but does not include other Item 18 information (see below), also suggesting that the intention is simply to transmit DOF/ changes in CHG, CNL, DLA, DEP and RQS messages, rather than the full Item 18 information.
 However, recognising that in automated systems the technique of completely overwriting a full field rather than amending a small portion of a field is commonly used, the meeting realised that it was possible that the new requirement to transmit the entire Item 18 in CHG, CNL, DLA, DEP and RQS messages was necessary. However, the Task Force would study whether adoption of a regional constraint that would result in DOF/ being the only Item 18 information included in CHG, CNL, DLA, DEP and RQS messages was at all feasible. The meeting considered that an urgent clarification was required in this case, as it could not identify any advantage to including full Item 18 data and either the routine transmission of bulky data or adoption of a regional constraint would undoubtedly cause global message processing problems.


(1) Category1

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In the mentioned example please note that there is no change in the date of flight identified in Item 18. The changes are in Items 8 and 16 as described in Field Type 22. It is agreed that in the messages concerned there is no useful reason to put all Item 18 information if there is no change in the referred Item. Field Type 18 in a CHG message shall not contain the changes. They go in Field Type 22. Field Type 18 with DOF specified in such messages it is meant to uniquely identify the flight when the FPL is presented more than 24 hours in advance and there is no need to include all the other Item 18 information in those messages.


Created at 05/11/2013 1:38 PM by Hu, Susan
Last modified at 05/11/2013 2:54 PM by Hu, Susan