Currently in the 10th Interval, Ista Weyr has re-organised its wing structure to allow riders to focus on Interval-related duties, rather than the strictly Threadfall-related drills of the former system.
Ista's Interval Wing system consists of three wings:
Each wing is responsible for different aspects of Interval dragonriding. These duties are explained in more detail on the individual wing pages, linked above.
The drills that the wings were responsible for conducting during the Pass are now done on a rotational basis. That is to say, wingleaders are responsible for organisation chunks of their wings to drill with chunks of other wings, and there really is no common group that will practice together.
The IC logic behind this is that it brings more attention to the actual Threadfighting skills that are in danger of being lost in Interval, rather than focusing on learning the flight patterns of a certain group that will never see Thread together.
The OOC logic of this is that, with a smaller player base, anyone can RP Thread drills with anyone, regardless of which wing they belong to.