It's done by seniority order and by category- APD (they can do everything), PCP (they can do the recommendation rides, ie the period before manuevers validation as well as before the LOE, as well as recurrent checkrides and the procedures validation), and then SLI which is the basic line instructor.

You order your preferred sim periods (C D A B E for me), your 4 golden X days and your 2 X days, as well as days you want to avoid like A and B if you have something going on in the morning.

You also preference how many in a row you prefer- I prefer small groupings, while the commuters of course prefer the long groupings. I routinely get groupings of 2 or 3, then 1 or 2 days off. Typically it's 12 or 13 days off, depending on how many doubles I do.

The schedules are hand built by the training planner, so having a good relationship with them really helps out!