If you only want a chat seeing in monitor, use sideChat.
eg: player sideChat "Where are you, we are waiting for you..."
But if you want call the air support in radio, put a trigger and set the type: RadioAlpha, named the Text field: "Air support" and write in the onActivation field:
airsupportstart=true; player sideChat "We need air support!!!"
And put the AH64 somewhere and his waipoint Condition filled: airsupportstart