The contract calls for UPS to create a certain amount of full-time jobs per year. I don't know the true amount, but its somewhere around 2,000 per year. I think your air-combo job is safe. If you do get laid of you have the right to bump 2 part-timers, so I wouldn't worry about it.
Sorry to come off on a tangent here, but the best job I ever had at UPS was the combo air-midnight sort job I had back in '00.
It really was the Good Ole' Days. Fed-ex and DHL weren't taking our volume and I was getting about 11 hours per day. I would start at 445 pm , pick up letter boxes until about 830 and then go to the airport by 9. By the time I got back to the hub it was around 1030 and the midnight shift was starting at 11.
I would then work the slide until about 330 am. The sad thing is they wanted me to stay until I hit 12 hours on some occasions.
This job will never exist in the current enviroment. Fed-ex ground and DHL are eating our respective lunches. Now, the full-time combo guys are strictly regulated to about 8-8.5 hours, but never going over 9.5 like I used to do on a daily basis in '00.
It was a great job during a great time. Problem is the competition is on our ass and those days are gone. I hope in the future when I'm 60 I can rely on a job like this one.
Thanks and sorry for the long post,
ML