Or is it a real world thing? And if so, where would I see that on an approach plate?

22 minutes ago, bahnzo said:

Or is it a real world thing? And if so, where would I see that on an approach plate?

Real thing. See the DME info as pointed to by the red arrow (14.4NM) on the first ILS chart below. There is no such DME info on the second ILS chart below. These are FAA charts. Jepp charts (i.e., Navigraph charts) will have similar info.

Al

Edited September 12, 20241 yr by ark

Thanks, I guess that part about "use the DME" should've gave it away! I guess I never noticed it until it's not there. 

6 minutes ago, bahnzo said:

Thanks, I guess that part about "use the DME" should've gave it away! I guess I never noticed it until it's not there. 

On the first chart above, the DME info is provided by the Localizer signal. In other cases, the DME info might be provided by a DME or VOR-DME station located on the airport and not the Localizer signal itself.

Al

 

Edited September 12, 20241 yr by ark

Nowadays everything is provided GPS.

Maybe someone could explain to me why in Europe ,and I believe the majority of places the ILS DME reads zero at the threshold. Whereas in the US it will typically read something like 1.8nm.

Is that because as mentioned above the DME signal is colocated with the localiser , the antenna for which would be situated at the far, stop end of the runway you are approaching, which would tie up to that typical 1.8nm distance? And I guess the rest of the world had a separate DME station located at the approach threshold?

I seem to have possibly answered my own question ! Every day is a school day.

1 hour ago, jon b said:

Maybe someone could explain to me why in Europe ,and I believe the majority of places the ILS DME reads zero at the threshold. Whereas in the US it will typically read something like 1.8nm.

Is that because as mentioned above the DME signal is colocated with the localiser , the antenna for which would be situated at the far, stop end of the runway you are approaching, which would tie up to that typical 1.8nm distance? And I guess the rest of the world had a separate DME station located at the approach threshold?

I seem to have possibly answered my own question ! Every day is a school day.

Yes. 

2 hours ago, jon b said:

Is that because as mentioned above the DME signal is colocated with the localiser

I wouldn't say the majority of Europe uses dme's calibrated to zero at thresholds, certainly a few do.

The antenna may be located with LOC/GP or elsewhere. EGLL for example has the antenna placed mid-point of the runway serving both ends calibrated to read zero at the thresholds. Trickery.

26 minutes ago, srcooke said:

EGLL for example has the antenna placed mid-point of the runway serving both ends calibrated to read zero at the thresholds. Trickery

Most interesting, thanks.

8 hours ago, sd_flyer said:

Nowadays everything is provided GPS.

That is not correct.  Most ILS approaches still use traditional ground-based equipment to define all approach fixes.  While a pilot might use GPS to locate those fixes, a GPS is not required in order to fly the approach and approach fixes are not GPS defined waypoints.  What is true is that there are now some hybrid ILS approaches where GPS based fixes are used and an IFR certified GPS is required in order to fly them.  When this is true, the requirement for GPS will be noted on the approach plate.

A good example showing both is provided by the two ILS RWY 19 approaches at KJAC.  The ILS Y approach is a traditional ILS, entirely ground based (other than the radar vector entry of MOSS, where radar services are required) and the fairly new ILS Z approach which features GPS fixes and carries a notation of the requirement on the plate.

 

Scott

It is the very fact that there are ILS approaches that use another DME source (such as a VOR) for DME that I get so upset at the design of modern avionics that auto-tune the approach frequencies on both NAVs - this knocks out my pre-tuned alternate reference for distance on  NAV2 and I find myself having to re-tune it while in the approach.

1 hour ago, tttocs said:

That is not correct.  Most ILS approaches still use traditional ground-based equipment to define all approach fixes.  While a pilot might use GPS to locate those fixes, a GPS is not required in order to fly the approach and approach fixes are not GPS defined waypoints.  What is true is that there are now some hybrid ILS approaches where GPS based fixes are used and an IFR certified GPS is required in order to fly them.  When this is true, the requirement for GPS will be noted on the approach plate.

A good example showing both is provided by the two ILS RWY 19 approaches at KJAC.  The ILS Y approach is a traditional ILS, entirely ground based (other than the radar vector entry of MOSS, where radar services are required) and the fairly new ILS Z approach which features GPS fixes and carries a notation of the requirement on the plate.

 

Scott

Just because the approach fixes are defined as DME or cross-tuned fixes does not mean that they are not also defined as GPS waypoints.  Many traditional navaid-based approaches are in the FMS databases as GPS "overlay" approaches, where the fixes are indeed present in the database, and though the approach was designed to be flown only with ground-based navaids, at least portions of the approach *may* be flown with reference to those GPS waypoints.  In the Gulfstream IV/V, we referred to the difference as "blue needle" vs "green needle"--when flying using GPS the HSI course indicator is blue, and when in VOR/ILS the CI is green.

The navaids required for the final approach segment of the approach are in the approach title--e.g. an approach titled VOR RWY 12 requires you fly the approach by reference to a VOR course.  An overlay approach will be titled something like VOR OR RNAV RWY 12. 

Even on a non-overlay approach, you can still put the GPS-derived course up as long as you also display the course using the "primary" navaid.  When you're in central Africa flying to a place with nothing available but an NDB approach, and thunderstorms all around are making the ADF needle swing like a windshield wiper, that rock-solid blue-needle overlay is an awesome thing to behold.

57 minutes ago, Bob Scott said:

Just because the approach fixes are defined as DME or cross-tuned fixes does not mean that they are not also defined as GPS waypoints.

Agreed.  As I said, they may certainly be, and often are, flown using GPS to help identify the fix.

59 minutes ago, Bob Scott said:

Many traditional navaid-based approaches are in the FMS databases as GPS "overlay" approaches, where the fixes are indeed present in the database, and though the approach was designed to be flown only with ground-based navaids, at least portions of the approach *may* be flown with reference to those GPS waypoints.

Again, agreed.  But an overlay approach is a whole other thing, explicitly allowed to be flown with either GPS or the ground-based navaid and certified and explicitly noted as such.

What I was addressing with my post was that "it's all GPS now" in reference to an ILS approach.

 

Scott

2 hours ago, tttocs said:

That is not correct.  Most ILS approaches still use traditional ground-based equipment to define all approach fixes.  While a pilot might use GPS to locate those fixes, a GPS is not required in order to fly the approach and approach fixes are not GPS defined waypoints.  What is true is that there are now some hybrid ILS approaches where GPS based fixes are used and an IFR certified GPS is required in order to fly them.  When this is true, the requirement for GPS will be noted on the approach plate.

A good example showing both is provided by the two ILS RWY 19 approaches at KJAC.  The ILS Y approach is a traditional ILS, entirely ground based (other than the radar vector entry of MOSS, where radar services are required) and the fairly new ILS Z approach which features GPS fixes and carries a notation of the requirement on the plate.

 

Scott

No Scott, 

Most ILS approaches here in US pretty much retired most of tradition marker beacons system and substituted them with GPS fixes. Yes explicitly GPS is not required and yes some fixes can be identified with cross radials, DME, or ATC radar, but in reality we all load ILS approached into GPS . This is smart way to go!

In recent years GPS is no longe luxury but necessity! RNAV approaches become pretty good alternative to ILS . Especially when ILS goes  down i and  localizer minimus are too high to penetrate low ceiling.

In your example of KJAC airport LPV minimums for GPS 19 Z are in par with ILS 200 feet AGL! I can tell you from my experience over 20+ years of flying and half of it as flight instructor -nowadays there is "no go" without IFR certified GPS!

Ground equipment is flimsy and breaks all the time - repairs are costly and waiting time is very long! GPS is pretty much our savor. I remember some time ago we had a jet run out of runway, crashed and destroyed glideslope transmitter. After glideslope transmitter was rebuilt,  we were waiting  over three months for FAA King Air re-certify ILS approach again (due to their  backlog)!  Thanks for three GPS approaches at my airport we were operating without ILS just fine! In contrast, if were to stuck with traditional localizer and VOR approaches with very high minimums most ops would just ceased, especially during time of all days of low marine layer.

And another ILS DME question for US based pilots…

When the controller says maintain 160kts to a five mile final, are they referring to 5 miles out from the runway so a DME reading of 6.8 (5+1.8 readout at the threshold)or 5 miles indicated on the DME ?

I’m aware the last point they can legally apply a speed restriction is the FAF which would normally be at around 5nm physically from the threshold so 6.8 DME so again have kind of answered my own question. 
I’ve always used 5+1.8 however it would be handy to know definitively what you guys do ,as I'm finding a lot of FOs now are thinking it’s 5 DME and short finals isn’t the place to start a conversation about it.