ICAO text NOTAM are transmitted over AFTN and have to comply with certain technical limitations of this network. One such limitation concerns the maximum length of a message - 1800 characters. A message longer than 1800 characters needs to split into a “multi-part” message, but this split also is limited to 26 times. However, a NOTAM that would need more than 26 x 1800 characters is unlikely to exist, as it would seriously break the ICAO rules for information publication by NOTAMs.
NOTAM messages that would require to be split into up to 5-6 parts for AFTN transmission are likely to be encountered from time to time. From the point of view of the Event Schema, they should be treated as a single NOTAM messages and stored as one (consolidated) NOTAM object instance.
The split will occur only for AFTN transmission purpose. In addition, it is recommended that a series of warnings are displayed by a Digital NOTAM encoding tool to the operator, as follows:
- a first warning message shall be issued when the length of the item E of the automatically generated NOTAM text exceeds 300 characters;
- when the automatically generated ICAO NOTAM reaches 1500 characters, a first warning should inform the operator, but without any other action;
when the automatically generated ICAO NOTAM reaches 1800 characters, a second warning should inform the operator that the NOTAM will be split for AFTN transmission purpose into parts of maximum 1800 characters each. As an optional feature, the tool could offer the possibility for the operator to see and eventually decide on the splitting point within the automatically generated item E.