Military slang for getting assigned to Fleet Assistance Personnel. Basically it's when your unit is required to temporarily send X number of warm bodies to do menial tasks for the base or the squadron or something, and you're picked to be part of the group. Occasionally a cool gig and a welcome break from routine, but a lot of the time it's something godawful and involves Twentynine Palms or the term "grease trap". Usually assigned to new arrivals as a rite of passage, and to shitbags that aren't wanted in their unit
"What happened to Johnson? I haven't seen him in ages."
"He kept fucking up so he's been fapped out to 990 for over a year now."