Seniority number 1800 with 4 days available will get a 4 day trip before seniority number 1900 with 6 days available will.

First comes day matching (4 day trip to 4 day reserve), within that list irst bid-to fly folks from high seniority to low, then regular reserve from low seniority to high. If there are no day matching, then day match+1 (4 day trip to 5 days available), bid to fly, non bid to fly, etc.

That's why on a string of 6 days of reserve it can be hard to get a trip, since we have no 6 day trips, they must go through all 4 day and 5 day reserves.