Day VFR equipment | Civil Aviation Safety Authority
The flight and navigational instruments required for flights under visual flight rules are:
- an airspeed indicating system
- an altimeter, with a readily adjustable pressure datum setting scale graduated in millibars
one of the following- a direct reading magnetic compass or
- a remote indicating compass and a standby direct reading magnetic compass; and
- an accurate timepiece (clock or watch) indicating the time in hours, minutes and seconds.
CAO 20.18
Other aircraft in private, aerial work or charter operations
3.4 Subject to paragraph 3A.3, an aircraft:
(a) engaged in a private, aerial work or charter operation; and
(b) not mentioned in paragraphs 3.1 to 3.3;
may only be operated under the V.F.R. if it is equipped with the following:
(c) the instruments specified in Appendix I;
(d) any other instruments and indicators specified in the aircraft’s flight manual.
So what does your Flight Manual say? If it says you require 2 then that would be why, also, is the remaining Radio properly certified for use? Wouldn't be the first time one has been installed and certified with a cheaper backup that wasn't.