That is a local practice. Here, no part-timer is going to bump a FT 22.3 off vacation. I pick before 30 year part-timers. Also, according to the contract, unless you have a specific bid (you are bidding start times and/or route), no one can pick a specific load or unit..you are put where you put. The only language says "age and physical condition will be considered", nothing about seniority. Also, any preferred job should go to a part-timer, given the 22.3 already has one "preferred" job half. However, no part-timer is going to bump a FT off of their preferred job.