Ortac
We are talking to different things here, you check the DME audio ident ( or if you are lucky the machine can do it for you ) and you can be sure you have the correct station.
My objection to GPS for DME in Europe is the large number of radio aids that are quite closely located, punch in the incorrect identical nav aid and you are likely to get a plausible distances ………. so it looks correct, a DME ident that is wrong sounds wrong.
In the USA identical NAV aid indents are not used within 500 miles making a distance from an incorrect entry immediately inplausable, that is the safety built into the American system that is not built into the European system………. yet.
If I had a £ for each time I have seen a wrong waypoint almost executed in an FMC and trapped by the other guy I would have retired by now, GA pilots don’t have the “other guy” to do the checking so the almost co located identical waypoint is a trap in the making for European users of DME substitution by GPS.
Technically the actions of your IR examiner was wrong, but I am guessing you were not flying this approach anywhere near the limits and he would have considered the GPS substitution a better demonstration of your skills, the fact that you flagged up the correct way to fly the approach showed that you are up to speed with the regulations.
I agree with A_and_C. If you change the frequency on any radio, in any way, you re-identify the aid. That includes accidentally hitting the frequency flip-flop on the NAV radio and immediately flipping back. Just in case. Very annoying in the case of a DME with the ident only every 30 seconds, but still.
Personally, I don’t think that the auto-ident adds much as it is not any faster than listening to the Morse code yourself.
But two different DMEs on an approach are quite rare, compared to the typical case of a final approach DME, on occasion also used with a DME arc.
A lot of approaches which require DME allow ATC to give you DME distance for glide slope checking purposes if your DME is inoperable – this then requires that ATC have radar available. The approach plate will state this.
In the same vein if an NDB is required on the missed approach, you can advise ATC that you need a different missed approach if not NDB equipped.
A_and_C wrote:
Once you tune the DME away from a station you are required to ident it when you return to he station…
Ok maybe we are slowly chipping away at the misunderstanding here… 
I think you are saying that although I did not twiddle any frequency dials after identifying both DME channels, the act of subsequently flipping the DME source switch from Nav 2 to Nav 1 is technically retuning…and therefore demands re-identification…. if that’s the case then I am guilty as charged….luckily this has not been picked up on any IPC flights….I will change my ways!
Teal wrote:
Perhaps you should present your case for GPS in lieu of DME to the Regulator…in this case EASA?
Here’s how they do it in Oz.
Any IAP chart that has that statement allows you to substitute the DME by GNSS. Any IAP chart that does not have the statement… you need an actual DME.
Anthony Q
That is indeed correct.
I think with modern DME channeling normally using serial data the chances of mis-tuning are remote but with the older type of slip code devices there was a real chance of the mechanical tuning slipping a tooth and mis-selecting a frequency, in fact the death of things like the King KX170 & KR85 was most likely to be due to the mechanical bits failing rather than the electrical bits.
Archie wrote:
Any IAP chart that has that statement allows you to substitute the DME by GNSS. Any IAP chart that does not have the statement… you need an actual DME.
Now THAT is the way to go – thanks for sharing !
Now that is a good idea. Is it just Australia that does this or any where else?
@ortac
ortac wrote:
I agree, being too high on an approach is not ideal. But not really dangerous either, if the pilot is aware of this effect. If everyone could accept that the above is the only technical issue associated with GPS-for-DME-substitution in Europe (i.e. ignoring human factors and training issues), then we can debate how much of an issue and how dangerous it is. But right now, most people seem to be sticking with “substituting GPS for DME is just stupid and dangerous, period”, without saying why.
I agree with you.
I don’t want to debate wether DME substitution is a dangerous or not. By definition risk perception is a subjective matter so we won’t be able to reach an agreement across the EuroGA.
However I think it’s important that one understands the side effects of DME substitution and makes a risks assessment based on the evaluated side effects.
For your information, these last years we have been working on unstabilized approach prevention at work.
Indeed according to the flight safety fondation stabilised approach are about 60 times safer than unstabilised approach.
A significant part of accidents during landing (airlines or light GA) have “unstabilised approach” as a contributing factor.
The light GA document is in French, but I guess the images are self-explicit.
When we practice ILS approaches at EBLG, 05R has two DME references: LGE which is at 0.5 NM of 23L threshold and IHH which is linked to the 05R ILS at the 05R Threshold. As it is a DME required approach, we dial a direct to IHH and we have our GPS DME on the top row of the G1000.
Of course it is not legal but it is not more complicated than dialing the good DME frequency in a real DME and we have a accurate distance check.
I guess this trick can be used at other airports with offset DME.
