Jtrizzy said:
Question: When you get an airstrike, UAV, or chopper, how long does that stay with you? Obviously you can die, but is there a certain amount of time/deaths before you have to use it?
IIRC, UAV & Chopper last for 30 seconds after you launch it. Airstrike kicks in a few seconds after you call them in; there's 3 Payload drops.
Here's the thing with UAV, IIRC UAV's do not stack, meaning if your teammate sets off a UAV, set your UAV off when your teammate's UAV ends...this maximizes your UAV.
With regards to how long they stay with you, as mentioned by lionelhutz, getting an Airstrike will over-ride your UAV, and getting a Chopper will over-ride your Airstrike...I'm not sure if getting an UAV will over-ride your Chopper though.
Regarding Choppers though, depending on circumstances, you may or may not want to try to chain your Chopper calls...meaning once you get a Chopper, you can call in the Chopper whenever you feel like, even after you die (assuming it can not be over-ridden by a UAV). In general, what people (including me) tend to do is get the Chopper, die (either kill yourself (cook a frag, jump off a roof) or go Gung-Ho), and then call in the Chopper when you re-spawn. If you can keep yourself alive, the Chopper kills will count towards building your next UAV-Airstrike-Chopper count.
Edit: Re-reading your post, it seems like you may already know this...apologies...I'll leave the post intact as is, in case it helps others.