1.Add a trigger in the editor, area 1000-2000, place 50 OPFOR units in it.
2.Place a blufor helicopter far away, and player as driver.
in the trigger's condition: vehicle player in thislist (above, put anyone or blufor and present; or you can also group the trigger with the player's vehicle).
3.In activation: hint "hello world".
4.Fly until the trigger's area, but do a save 100m before you get in.
5.Get in and load, many times, you'll see that you don't get each time the message.