HF.
Standby machines are on site at each of those bases. They are not, however, fully fitted a/c. ie. No auto hover & single hoist but are fitted for FLIR. This is just swapped from a/c to a/c and takes the engineers less time than it does for the crews to swap their equipment.
Again, it comes down to what the client is willing to pay for.
Allegedly the new a/c, S92 and AW139 will all be the same. That is, fully coupled, dual hoist etc.etc. We shall see.