For example, the gunshots heard,.
Webthe helicopter event is one of metagame events.
It occures only once (unless it's altered in the sandbox settings prior to starting a playthrough).
The helicopter event will occur.
Webif you find a radio, leave it at your base, tune the radio to that frequency and check it at 9am every morning.
When the radio announces ‘air activity’ today or tomorrow, then on that.