Well, I stand corrected. In my case there is no direct discussion with the airline, it is up to my group to give the oppinion (based on analysis) if the inspection interval can be extended.
I assume this is the correct course of action (the one GHLCarl explained).
Info and requirements for extensions were comming to us straight from the airlines (telexes or through FSR).
In terms of who can authorize an extension - a DER at OEM can do this (at least for structure which is my turf).Of course it depends whihch level of authority it has.
CAA has no expertise to guve such opinion (at least from what we can see) appart from asking an OEM for opinion.