It doesn’t seem to me to be a vexed issue, at least in so far as Norfolk Island and its associated territorial airspace are concerned: Airservices Australia is responsible for ‘Australian-administered airspace’, and that includes Norfolk Island and its associated airspace (as defined). Airservices Australia might choose to discharge that responsibility by entering an agreement with someone else, but it’s up to Airservices Australia to ensure the agreement results in the appropriate levels of service in ‘Australian-administered airspace’ as defined in the Airservices Act.
For completeness’ sake, I copy QSK?’s post in another thread:
I think the responsibility for providing the FIS for YSNF "fell through the cracks" between the Australian and NZ civil aviation agencies when the Norfolk Island FSU closed. And the NZ AIP references would appear to imply that NZ still thinks the FIS responsibility for Norfolk Island lies with Australia.
As you would be aware, prior to its closure in the '90s, the NF FSU used to hold the FIS responsibility for advising aircraft on NF weather during its hours of operation even though it was located within the Auckland Oceanic FIR. Outside of the FSU's hours of operation, the FIS responsibility reverted to the Sydney FSC and subsequently to the BN FSC when the Sydney FSC was closed. My understanding is that the FIS responsibility was totally transferred to the BN FSC when the Norfolk Island FSU was finally decommissioned.
I'm proposing the view, that the issue of Norfolk Island FIS responsibility may have been overlooked by Airservices/CASA/CAANZ/Airways either when the FSU closed or with the subsequent institutional changes implemented by Australia (i.e the integration of ATC/FS functions) as well as the change to the Flightwatch "self help concept" in lieu of the directed FIS.
It's this issue that requires investigation and comment on by the ATSB and, if necessary, be the subject of a safety recommendation so that the appropriate MoU/LoA remedial action, as you have proposed, is implemented between the Australian and NZ agencies so that we don't have a repeat of this situation again in the future.
If anyone can identify any flaw in QSK?’s reasoning, I’d be interested to hear about it.
However, I say again, that none of this appears to answer the question as to who is responsible for providing what services to whom, and to what standard, in ‘international’ airspace.