OM & MM & IM's

[Jack Ranga]

Does anyone know what the policy on marker's is? Are they ripping them out, in particular the OM's? There'd have to be at least a MM for a Cat II or III ILS wouldn't there?

How many Cat I ILS's in Australia still have OM's etc??

[seneca208]

No Markers on NZ ILS approaches, including the Cat 3 in Auckland- So I guess Australia could go without them.

[Jack Ranga]

That's interesting, especially for a Cat III :sad:

[waren9]

dunno if they're being decommissioned. handy for a positive check height in case an associated dme goes out and still allowing the approach to be flown although many in oz seem to have "dme reqd" regardless

ymml 27 and ypad 23 off the top of my head for a start, so lots i guess

[goodonyamate]

Isnt it a requirement to have a marker to be able to apply special alternate minima.......

[Oktas8]

Good question Jack.

To fly an ILS - any ILS - all you need is a LOC, GP and altimeter.

To check the integrity of an ILS all you need is some form of distance measurement - DME, GPS, radar fix or marker all qualify.

Given that just about every IFR aircraft in Australia has either a DME or TSO certified GPS, and certainly every aircraft can acknowledge a radar fix, the real question for me would have to be "why are there still marker beacons in use?"

Restrictions on using GPS in lieu of DME for certain ILSs are a legislative requirement not a technological one. If you want distance to the IKN glideslope array, point your GPS at the correct IKN beacon. Just as you would if you wanted distance to the SY VOR.

Edit to add: why would you need a marker beacon for Low Vis Ops? Not an area I'm familiar with, but I don't see an obvious technological need for it.

[27/09]

There'd have to be at least a MM for a Cat II or III ILS wouldn't there?

To put it simply, No.

[Jack Ranga]

Anybody know if ASA's policy is to turf them?

Why do some ILS installations in Aus have them and some don't?

[alphacentauri]

Restrictions on using GPS in lieu of DME for certain ILSs are a legislative requirement not a technological one. If you want distance to the IKN glideslope array, point your GPS at the correct IKN beacon. Just as you would if you wanted distance to the SY VOR.

I do get your point, but its not quite that easy. But the problem is easy to fix. An ILS installation usually comprises of 3 things LOC, GP and DME. In fact ICAO have mandated that ILS must have its own independent DME and this hasn't always been the case.

When an ILS is stored in an aeronautical database the ILS, GP and DME all have the same ident and so to store in a gps unit we can only give you one ident and position to select from. Traditionally (and because of the requirement above) the position selected to store with the ident was the position of the localizer. This means when you select IKN you are selecting the position of the LOC antenna, and that is why GPS cannot be used in lieu of DME for these procedures. The solution is to store the DME location, but this might take a while to catch on if ever. The prime reason not to, is that the DME is not the aid providing track....but this where it would all get political.

Alpha

[Oktas8]

In fact ICAO have mandated that ILS must have its own independent DME

I didn't know that. So I guess more and more ILSs will be converted, in time.

You mention three locations, but in practice it seems to be two positions in the FMS (GPS) database, probably because the FMS (GPS) "knows" that the DME is effectively co-located with the GP array. Certainly the general aviation GPS units and turboprop FMS unit that I have used, offer the option of selecting either LOC or GP location for any given ILS installation.

As you mention, one does have to know which database entry to use, which is a potential error and takes a little thinking about.

Cheers,
O8

[waren9]

and that is why GPS cannot be used in lieu of DME for these procedures

not the case for ypad ils 23 i believe

gnss permitted in lieu of dme, ref pt ad vor

or am i on the wrong track? (so to speak)

[UnderneathTheRadar]

Avalon has ILS-Y and ILS-Z for each of the two DMEs - ILS Y allows for DME GPS to be used in lieu using AV as reference. ILS-Z doesn't allow GPS in lieu of IAV (GP) DME.

[alphacentauri]

O8,

Yes more DME's are coming. Sydney just finished. Adelaide and Cairns currently being done. Eventually they will all have their own.

I didn't know you could select the gp. Good to know these things. The possible error in selection between the two is probably why they have hit it with the broad brush of prohibition


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[Oktas8]

Alpha,

You seem to know something about these things. I have a question unrelated to ILSs, if I may thread drift for a moment.

In Oz, one may fly a DGA using GPS in lieu of DME. However, if using the GPS, it must be referenced to the tracking navaid not the DME. Given that one is using the GPS solely for distance (not tracking), and given that all distance arcs on the IAL chart are referenced from the DME, why are we not to reference the GPS to the DME?

Thanks,
O8

Don't even get me started on comparing GPS azimuth to NDB azimuth and ensuring that they are within 6.9° of each other...

[QSK?]

Alpha:In fact ICAO have mandated that ILS must have its own independent DMEIt's not mandated by ICAO but States do have the option to provide DME in lieu of marker beacons provided that the DME triangulation displacement is less than 20 degrees from the LLZ centreline and the distance accuracy falls within +/- 0.2 nm.

The choice to use DME in lieu of marker beacons, in areas where terrain constraint is not an issue, is invariably simply one of cost; States only have to maintain only a single system (the DME) instead of 2 (OM and MM in Oz) or sometimes 3 (OM/MM/IM internationally).

[ROTOR BLAST]

Location of any ASA ground-based hardware outside the boundaries of Commonwealth Leased Airports e.g NDBs, VORs and Markers must be on the liquidating list. Revenue derived from the sale of these tax-payer owned assets can be used elsewhere on much more important projects1:ugh::ugh::ugh:

[ROTOR BLAST]

All ASA assets located outside Commonwealth Leased Airports must be fair game at the moment - NDBs, VORs and Markers.......
Some NDB sites are worth millions which can be re-directed into far more worthwhile projects like training new ATCs in Timbuktu!:ugh::ugh::ugh:

[alphacentauri]

QSK, I had been told it was an ICAO mandate. Clearly I have been misguided. I do think its a good idea as it gives us all more flexibility if dme's become unavailable. I also wasn't aware it had to do with marker beacons.

Oktas, where the vor/dme is co-located I think we reference the vor as the distance reference. The only time we specifically reference the dme is if it is physically separate from the vor. I'll have to check to confirm this


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