Hi

can anybody please confirm if the CIR set nine question 5 answer is right.
the question says that you have not met the recency requirement for an RNAV Gnss approach, this is a flight from Winton to Longreach.. the answer says that you can descend down to the gnss minima of 1710ft before you first cross the Longreach VOR.. I thought that if you do not meet the recency requirement for GNSS approach, then you can only use the GPS for distance but the lowest altitude you can descend to before first crossing the VOR is the 10nm MSA..

please do correct me if I am totally wrong or might be missing out on something here...

any assistance is highly appreciated..

BUMP

AGAIN

Clearly these questions need clarifying, as a lot of people are getting stuck on it. Be great if someone could take a moment to clarify why the GNSS circling minima is used over the NDB minima or the MSA for that matter. Cheers

I think you may be confusing a GPS Arrival with an RNAV/GNSS approach. If you are not current on an RNAV/GNSS approach it does not mean you can't do a GPS Arrival. A GPS arrival uses the GPS for distance information only while the tracking is done by reference to a ground-based aid (VOR or NDB). You don't have to be current on an RNAV/GNSS approach do do that.

Thanks Bob I think I understand now. I wasn't confusing GNSS arival with rnav gnss approach, but what i was getting confused was the actual meaning of MDA, thinking that that could be the height you could be at before passing the NDB (or VOR). Keyword being BEFORE. You cannot be at MDA before crossing the aid, you must be at MSA or higher, correct? So if you choose to do a GPS arrival, in this question's case the circling minima would get you lower than the MSA, which is the lowest height you could be BEFORE crossing the aid if that's what you were using for your entry. Correct me if I'm wrong?

If you are on the NDB approach, the MDA is the lowest you could descend before crossing the aid unless you are visual in which case the visual or circling minima come into play (depending on whether it is day or night).
If you are on the GNSS arrival, the minima of the arrival is the lowest you can go until you cross the aid you were using for tracking guidance - again unless you got visual first.
If you are not using any approach or arrival procedure, MSA is the lowest you can go before crossing the aid.

Theses questions infer you have not got visual during your descent so "how low could you go?".

Cheers,

Rich

Now you have confused me again, Rich. I understand that if you were visual and during the day then the 300 feet rule applies, but I thought even that was after passing over the aid? If what you say is true and we can go down to the NDB MDA before crossing the aid (in this question was 1250ft) then that is lower than the DME/GNSS arrival circling minima of 1710, and the argument still stands as to why we wouldn't use the NDB MDA over the DME/GNSS circling minima as the lowest possible height we can descend to before crossing the aid?

Hi jeffr,

You can't usually use the NDB minima for the descent before first crossing the aid because typically you must cross the aid to start the NDB approach. Oneexception would be if the approach could be entered via a DME arc for example. In that case, yes, you could look at the MDA of the 2D approach when deciding how low to go befpre crossing the aid. My comment above was to simply state if you want to know how low you can go in general, you use the lowest altitude that applies to the procedure you are using (the arrival procedure or an instrument approach).

If you add the additional condition "before you cross the aid" then you are restructed to selecting:
- the MDA for an arrival procedure, or
- the MDA for a 2D approach (VOR/NDB) but only if you don't have to start the approach at the aid, or
- the 10nm MSA

Usually in these exam questions, the approach available requires crossing the aid first before commencing the procedure - which is usually several thousand feet above the aid, at or above the 10nm MSA. This will be well above the MDA for an arrival procedure for the aerodrome. CASA is testing your ability to know you could use an arrival to get below MSA if you don't want to cross the aid first.

Cheers,

Rich

Understood. Thanks Rich