LB
On what frequency is one obliged to maintain a listening watch when you're in G but not in the vicinity of an aerodrome?
That is the choice of the PIC to make considering all the factors available to him/her.
Above 5000 ft I would suggest the Area Frequency. Above the lid of the MULTICOM and below 5000 there is no requirement, but the Area Frequency might be the best choice.
The idea is that with the MULTICOM you don't know when you are 'in the vicinity' of any strip etc, so using the MULTICOM is simple.
Let's say one of your students is going to fly from The Oaks (near Camden NSW) to Leeton (in the NSW Riverina), 'low level', VFR. The student will overfly Temora. The aircraft has 1 VHF.
In the system you are advocating, what frequency (if any) do you advise your student to monitor and broadcast on, at what positions, during that flight?
The choice for a VFR pilot is simple. If he/she is below the lid of the MULTICOM then 126.7 - When in 'in the vicinity' of a promulgated CTAF (on other than 126.7), then that frequency for the appropriate broadcasts.
IFR single VHF inbound from western Victoria to Moorabbin, intending to proceed OCTA below the CTA steps via PTOM.
What frequency should be set from 20 DME ML where the CTA step is C LL 2500?
if MULTICOM, what does the pilot do re SAR whilst out of comms with ATC?
if the IFR is on MULTICOM, how should ATC manage SAR & SIS?
I would expect that as an IFR category aircraft he would normally be given frequency transfers by ATC.
In your example, then he is perhaps changing to VFR procedures in which case he would monitor frequenies as directed by ATC or if he felt the need to change to another frequency such as the MULTICOM then he would advise ATC and nominate a time to call again (a sked). This procedure is used now with CTAFs and BAs.