DME/GPS Arrival

[Stationair8]

Conducting a DME or GPS arrival in YMTG.

If you use the GPS for distance information, it has to be referenced to the YMTG VOR.

I assume correctly that you can track into the aerodrome using either the NDB or VOR, as the chart shows both aids listed and also shows them as the MAPT.

Another pilot believes that you can only track in the VOR as that is the reference point listed.

I disagree but the AIP doesn't actually state that, just mentions the azimuth aid.

Over to pprune for discussion!

[AussieNick]

I read that chart as you can use the VOR or NDB on the sector A only, otherwise you need to be on the VOR

[MakeItHappenCaptain]

You must use the VOR for distance reference, but other than that, the "nominated" aid could be either the VOR or NDB as mentioned on the sector definition.

The missed approach point is also defined as either aid and as both aids are defined (freq and ident) on the plate, you are correct.:ok:

Notice the VOR and NDB approach plates (for which you must use the named aid) do not define the other aid.

ps, Aussie, a Sector A arrival is the ONLY available approach, there isn't a B or direct track...:rolleyes:

[AussieNick]

yep, just realised that after posting :}

Do have a question on this though,

ENR 1.1 - 37
19.4.3 states When using radio navigation aids as the primary means of navigation the aircraft must be navigated by reference to the aid which provides the most precise track guidance with wich the aircraft is equipped and the pilot is qualified to use.
The oder of precision is Localiser, GNSS, VOR, then NDB.

my interpretation is that, if you have VOR and ADF onboard, qualified on both, then in the above example, you'd have to use the VOR not the NDB, correct?

[Stationair8]

That is what iI thought, and that is what I have done since obtaining an IFR rating in 1989!

The gen Y four bar expert was babbling on about something and deemed it to be not what he would do blah blah blah!

We tried to explain our logic and gave him an example such as the Hobart DME arrival, which is based on the VOR only-but to no avail.

[alphacentauri]

AussieNick,

Your reference ENR 1.1 - 37 is valid for enroute navigation. A DGA is a considered to be terminal procedure (ie navigation in the terminal area) and so this reference is not applicable.

As the approach has been designed and cleared to either the NDB or VOR, then you are perfectly ok to use either, whether you have them both or not. I know I would use the VOR, but the point I am trying to make is that you don't have to in accordance with ENR1.1 -37

Just my 2 cents from a procedure design point of view

Alpha

[AerocatS2A]

ENR 1.1 - 37
19.4.3 states When using radio navigation aids as the primary means of navigation the aircraft must be navigated by reference to the aid which provides the most precise track guidance with wich the aircraft is equipped and the pilot is qualified to use.
The oder of precision is Localiser, GNSS, VOR, then NDB.

my interpretation is that, if you have VOR and ADF onboard, qualified on both, then in the above example, you'd have to use the VOR not the NDB, correct?

That doesn't pass the common sense check. If that applied to an instrument approach then you wouldn't be able to do an NDB for currency if the ILS was available.

[Oktas8]

I did the ATPL law exam about a year or two ago (foreign conversion). I remember one of the questions, as follows (my phraseology):

- You are tracking 200 to pass overhead an airfield. The airfield has an NDB and a localiser. The localiser final approach course is also 200. What should you use for tracking guidance, for the final 20nm? The answer of course is the LOC, regardless of what navaid you've been using up until now. I got that one right! :ok: It is of course entirely inappropriate for the enroute waypoint context, but it's in the AIP regardless.

It seems clear to me that it's contrary to the AIP to conduct an NDB approach in IMC if there is any other type of approach available for that runway.

Applying non-CASA-approved common sense, I think we all know what they mean by the rule, and it falls into the category of "good airmanship". On a fine day for training, do whatever you like. If the differences between navaids is going to be critical for airspace safety, use the most accurate one.

[strim]

In reality and for either case, surely you just track the GPS and monitor the aids for a 'significant disparity'.

[UnderneathTheRadar]

You are tracking 200 to pass overhead an airfield. The airfield has an NDB and a localiser. The localiser final approach course is also 200. What should you use for tracking guidance, for the final 20nm? The answer of course is the LOC, regardless of what navaid you've been using up until now. I got that one right! It is of course entirely inappropriate for the enroute waypoint context, but it's in the AIP regardless.

Interesting - what if you capture a LOC side lobe?

UTR

[ZAZ]

I am currently receiving instruction on DGA approaches and the charts I used yesterday state emphatically
USE VOR on NHL Arrival
USE NDB on WKB arrival.


And in my theory session the cfi pointed out accuracy of aids and pecking order protocol.


The other thing is we noticed as you track a radial of the VOR or an NDB homing to the aid is that you have to ignore the CDI deviation of the GPS as it will change wrt ARP especially in case where VOR is sited at a different point on the AD.


You should not fly the GPS course, you fly the heading/track to the aid.


2 cents.

[rmcdonal]

The other thing is we noticed as you track a radial of the VOR or an NDB homing to the aid is that you have to ignore the CDI deviation of the GPS as it will change wrt ARP especially in case where VOR is sited at a different point on the AD.

Don't set the airport as the destination in the GPS, but instead set the ground based aid and you wont have that problem, just make sure you set the right one.

[Hasselhof]

There will be a few minor differences depending on how you've got your GPS flight plan set up, and most of it comes down to personal preference.

For example

Destination airport code is YABC
The destination is served by an NDB with the code ABC
The reference point on the DGA chart for measuring distance is the NDB

Option 1
Have the GPS set up to take you to ABC, with ABC as the final waypoint in the GPS flight plan. If you did this then your GPS shouldn't enter terminal mode and will continue indicating your course cross track position on the enroute scale. Once you fly over the GPS reference point (in this case the NDB) the GPS has nothing to sequence to and should continue indicating a distance to that point.

Option 2
Have the GPS set up to take you to ABC, with YABC as the final waypoint in the GPS flight plan. Once within 30 nm the GPS should enter terminal mode and the GPS will indicate your course cross track position on the terminal scale. Once you fly over the GPS reference point (in this case the NDB) the GPS will sequence and now indicate a distance to the final waypoint which is the ARP for YABC.

Option 3
Have the GPS set up to take you to ABC, with YABC as the final waypoint in the GPS flight plan. Once within 30 nm the GPS should enter terminal mode and the GPS will indicate your course cross track position on the terminal scale. Select OBS or equivalent mode with the desired inbound course. Once you fly over the GPS reference point (in this case the NDB) the GPS will not sequence to the final waypoint until OBS or its equivalent has been disabled and continue to give a distance to the GPS reference point (in this case ABC). Once OBS has been disabled the GPS should sequence to the final waypoint (in this case YABC) and now indicate a distance to the final waypoint which is the ARP for YABC.

Why would you choose one over the other and why should you care? Simple. Know your GPS, what it is doing, what it will do, and find either the way you prefer, or the SOP that your company employs. Keep it the same, and understand the information it is giving you.

Personally, I use option 3 as I may not decide until relatively late in the piece that I want to do an RNAV over the DGA and having the destination (YABC) as the final point in my GPS flight plan makes the setting up of that approach quicker and easier in a single pilot environment. I also like having the GPS operating at a higher level of precision during the approach, and once OBS has been set, I set the desired inbound course on the CDI which facilitates checking for "significant disparities".

Final note, is that if your GPS is set up such that it will engage terminal mode, this should have happened before you reach the IAF of the DGA. If you are flying with precision in the first place it should not make a major difference to your day.

[Two_dogs]

The gen Y four bar expert was babbling on about something and deemed it to be not what he would do blah blah blah! POTY :} .................