Limiting number of mini copters?

Hi
Is it possible to add a limit on how many minicopters can be spawned. 

I want to have a special group on my server which can spawn x amount of copters 

minicopter.population

but if i'm right when u make population like 10 (how many mini copters will spawn on the map) you can have problems,when u spawn 11 mini 12 mini and every time when server will start save files that two mini will be removed from the map,but mby im wronge.

yeah i basically want to give a special group access to spawn their own copters and limit them to only spawn 5. minicopter.population will limit it for the entire map and i only want to limit this specific group?

Any ideas?