MINI TEST Q1 on page 171 of IREX

You are planning an IFR air transport flight into Coonabarabran. One GNSS unit has been removed for repair but all other aids are serviceable. The TAF is given below....
An alternate [is/is not] required. Why?

I said an alternate is required because they only have RNAV approach in Coonabarabran and we are operating with only 1 RNAV usable. The answer said You only have ONE C146a left so you can still fly the instrument approach. You would not require an alternate. An alternate is not required because you are equipped with two TSO146 RNAV/GNSS receivers.

As I understand it, you need 2 RNAV/GNSS or 1 RNAV/GNSS and 1 ADF or 1 VOR. An air transport flight must be able to suffer the failure of an airborne aid and still have means of conducting an instrument approach. If the one RNAV/GNSS that we have fails, we don't have the means of conducting an instrument approach.

What am I not understanding?

Coonabarabran had a ground-based aid when that question was written. I have changed the destination to Cooma-Snowy Mountaints.

Hi Bob, the current version of this question still quotes the TAF for Coonabarabran YCBB (and says "the TAF for Coonabarabran is...") although the destination is Cooma Snowy Mountains YCOM.

Thanks Baddles

I've amended the question

Cheers