If ALL avenues of hiring have been exhausted or just getting difficult & carriers have 120-day letters needing subs, mgmt can create a PTF position.
The PTF position is posted, bid on, & awarded like a route posting but ONLY for subs. The winning bid will be primary on 2-4 routes typically, works all Sunday Amazons (if applicable), cannot be assigned to an aux nor a "hold-down". A PTF cannot say NO to becoming Regular, they MUST advance prior to any RCA no matter the seniority. If a route does NOT have a sub on the matrix, a PTF gets preferential if they aren't working a route already.
If there are multiple PTFs, then seniority in bidding will come to play for them only. The position sucks since the pay can be less but it is a career position with benefits.