Guidance concerning Air Navigation in and above the NAT MNPSA
The line length must not exceed 69 character columns. Lines exceeding the Annex 10 maximum of 69 columns are invariably broken at that position by intervening AFTN communication centres, without any regard for content, causing the creation of unintelligible fragments.
Field 3: Message Type To be completed when the responsibility for originating flight plan messages has been delegated.
For filing of subsequent flight plans use either the “modification” (CHG) or “cancellation” (CNL) format as outlined in ICAO DOC 4444.
It is common for CNL messages to be received without a subsequent FPL message. This is equivalent to having received no flight plan at all. If an Airline Operator still intends to operate the flight, another FPL must be sent.
Also note that there is no guarantee messages are received in the same order they are transmitted. If a CNL (referring to a previous FPL) is sent and immediately followed by a new FPL it is quite possible that the FPL arrives first and is then immediately cancelled by the delayed CNL.
Creative use of time stamps does not help, it is the arrival sequence rather than the time stamp that determines how messages are processed. It is therefore recommended that a few minutes be allowed to elapse between the CNL and a subsequent FPL.
Another common error occurs when using CHG messages. Transmitting only those parts of a field that have changed is not acceptable because the new field will replace the entire contents of that field in the original message.
Field 7: Aircraft Identification (ACID) One of the following ACIDs must be included:
The registration marking of the aircraft (e.g. EIAKO, 4XBCD, N2567GA)
The ICAO designator for the aircraft operating agency followed by the flight identification
g. KLM511, NGA213).
The call sign determined by the military authorities if this will be used to identify the aircraft
during flight. Common Errors:
The ACID must not exceed 7 characters. An ACID of more than 7 characters will invalidate the message. Furthermore it will be impossible to manually correct the data as computer systems are only designed to handle the ICAO stipulated maximum of 7 digit aircraft identification strings.
The hyphen, often used in the graphical representation of aircraft registration, is also used as the field separator in all flight related ICAO messages and so must not be used in the flight plan ACID.
All-numeric ACIDs must be avoided. Even when the registration of a military flight is all numeric it is expected to be preceded by the operating agency descriptor assigned to the military operator in question.
Field 8: Flight Rules and Type of Flight
Insert one of the following letters to denote the category of flight rules with which the pilot intends to comply:
NAT Doc 007