Editors Depot - Tutorials - Getting Started - Mission Editor
There you will find everything you need, and much more
There is an example of a chopper being called in as air support - exactly the same principle as what you are asking - in the Tutorial Mission in Getting Started - Simple example missions
My own Macguba's guide to mission editing for beginners, in Getting Started - First Steps, has some tips on synchro if you need them, but one of the Mission Editor tutes will probably give you a lot more detail.