Ref: DHFS Type selection.
There was a fly off competition in 1996 with regard to both single and multi engined types for use by DHFS. Aircrew considerations were included which is a bit novel and QinetiQ & Boscombe kept out of it which is positively advantageous. The BK 117 and Bell Jetranger were both considered and flown at SHY in the competition tender. I believe the aircraft were supplied by the respective manafacturers such was the value of a prospective fleet purchase.
Elements that decided the eventual winners were no 'toy' undercarriage as students were likely to rip them off, and a cabin large enough to be able to cope with a rear crew student and instructor that had freedome of movement around the cabin without creating CofG issues and permitted winching and the lateral CofG loading that goes with having pilot / 'survivor +1' /winch operator +instructor all on the right hand side at the same time. Therefore skids were chosen for both types and the Griffin won over the BK117.
The DHFS Squirrel is I believe unique in its arrangement for both doors and transparencies (glass) to the point that attrition replacements have needed significant modification to get to standard DHFS appearance.
The aspiration to get a one-type-fits-all for DHFS will always be limited by the rearcrew requirements; therefore if I was a betting man, I would expect to see the squirrel around for some time whilst the Griffin could possibly be replaced with, or modified to a glass cockpit aircraft as that is the way front line helicopters either are already (Merlin) or will be shortly (Chinook).
Despite the ammount of UH1 that are decades old and still flying around the world, I am led to believe the Griffin life was only 15 years and then as they operate to FBH rather then Bell limitations to try and prolong their life. This may appear on face value a little draconian, so one must remember that the Bell 412 never was designed to be a trainer engaged in repetitive work cycles.