NAT Track Message Number (TMI) Calculator
The TMI of a NAT Track Message is based on the Julian calendar date for which the track system is effective. Enter a date to get the day-of-year number, and always confirm it against the date in the message itself.
Formula
TMI = the day number of the year, written with three digits. 16 January is 016 and 5 March is 064 in a normal year. A letter is added when the message is re-issued, for example 032A.
FAQ
What is the TMI used for?
Crews and controllers use it to confirm they are working from the same NAT Track Message, and it is included in abbreviated oceanic clearance readbacks.
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