The Gauntlet
I watched The Gauntlet on the weekend, great classic film with Clint Eastwood as a good cop trying to survive being taken out by other corrupt cops.
There's a Gazelle flown by the same guys from Blue Thunder which comes along and pursues him and his protected witness on a bike through canyons until they come to grief in a most dramatic ending.
Looks like they used an old Gazelle airframe or built an entire mockup to do the crash. They got the sound right, too!