They're similar to a "buildup" or a "relief" line you might have seen at other carriers. They take a mishmash of trips dropped for vacations, training, LOAs, etc. and build lines out of them. They're bid and awarded after the regular line awards come out. Coinflip if they're good or not.

VTO lines can have reserve duty, but you have the same contractual rights as a regular or hybrid lineholder.