BBC One Wales have released a short preview video for Helicopter Rescue, the documentary featuring Prince William and the Search and Rescue team at the prince's base at RAF Valley on Anglesey.
The Duke of Cambridge is shown piloting a helicopter on a rescue mission to a slate quarry in Blaenau Ffestiniog.
One of his crew are winched from the ground after rescuing a boy who had fallen off an old railway bridge onto rocks.
"As captain you're trying to play out the entire rescue, the transit to the rescue and back again in your mind, and pick up any circumstances or problems you can foresee, and try and fix them on the ground before you get airborne," he says in the programme.
More top news
See how your area fares.
The world's first ever 'hole in the wall' was installed in Enfield, north London, on June 27 1967.
America says it has "identified preparations" for an attack similar to that which killed at least 86, including 30 children, in April.