By the way, how are these call-signs, like Tartan 42, decided upon ? Is there a list of ones that have to be used in sequence, or do you just come up with them at the flight planning stage and make it known to ATC ? Many years ago, I sat next to a controller at Eastern Radar in Norfolk, around the time the first A-10s started arriving in the UK, and the A-10 he was looking after was called ' Yakker 19 '. I never did ask how the name was arrived at.
A blind guess here directed by nothing more than misguided logic It may be to do with the geographic area then specific location.. eg, Tartan being bonnie Scotland and 42 being the exact location of the dog track. Certainly, Tartan 42 is not a one-off but a regular sortie
Specific call signs are allocated to certain squadrons e.g. Tiger to 814, Jedi to one of the Harrier sqns etc. there's actually an official publication allocating them. There is generally some sort of logical link to the squadron though as they can ask for one to be nominated, for example 899 used to use Fist as one of their call signs and 800 or 801 used to use Hellcat because they used to fly them. I think the number is up to the squadron, but they're frequently allocated to specific pilots/posts on the squadron e.g. the CO is Skua 10 or some such. It changes a bit for formations where it'd be Vixen Lead, 1, 2 etc.
Of course if you're a small ship's flight once you leave the UK you can pretty much call yourself what you want as most air traffic agencies are more interested in why a small helicopter has just popped up on their radar miles from anywhere. Note to self must file flightplans more often...
That is most certainly true mate but doesn't quite apply to Tartan 42 in the same way as it's not a Squadron callsign but specifically.. a sortie. To all intents and purposes, the aircraft doing the sortie IS Tartan 42 for the duration of the flight but it might be something completely different on it's next flight.. unless of course, it flies the same sortie again