You have to keep in mind that in the Cirrus you have a large live approach chart that shows your position the approach. So the correct DME distance is not as relevant as in aircraft where the whole approach scenario is only numbers and bearings
That’s not correct… the moving map is showing only your lateral position. It isn’t going to show whether terrain is rising up to meet you too early, etc. The purpose of the DME distance is so you can fly the stepdowns correctly, or so you can check the SDFs if flying a continuous descent approach.
Do you have a moving map which also shows your vertical position, relative to terrain? I don’t believe any Jepp database based GA product does that.
The really big problem with doing this stuff is that in most cases there isn’t an obvious “DME=0” GPS waypoint.
The displacement programmed into the DME transponder.
Thanks for the explanation. That is indeed a very good reason not to substitute DME by GPS distance.
Part-NCO will go into force in August of next year in Germany.
That will an interesting time. Part-NCO does no longer strictly mandates DME for IFR. The (current) FSAV is in contrast with that. Germany has recently been known for ignoring (or at least absurdly bending) EU law with their own rules. We’ll see.
… maybe I should really delay buying that DME …. Thanks for the information!
Interesting news about Part-NCO. Good to hang around here :-)
… maybe I should really delay buying that DME …. Thanks for the information!
And hope you don´t get rampchecked after an IFR arrival in the mean time?
We are now in a period where the regulator doesn’t have the ability to always create sensible laws. Without suggesting one picks rules to adhere to (as it would be a dangerous precedent to suggest so), I do feel that any regulator who also mandates an ADF flown approach has no ambition of improving safety standards and therefore, one must excerise PIC privileges and use the safest method of completing a mission.
With that name, i am sure you’re biased :-)
And hope you don´t get rampchecked after an IFR arrival in the mean time?
I am already shivering ;-)
On an ILS, having no DME is not a big deal. DME “only” provides cross-checks, specifically
- cross-check of lateral position at glide slope intercept (prevents following a false glide slope)
- cross check of altimeter setting at glide slope intercept and/or an intermediate point(s) on the ILS.
Both of the above can be directly substituted with – and this is important – with the procedure tracks and the FAF WAYPOINT.
There is NO NEED to faff about with 2nd GPS waypoint (can’t do that anyway in G1000, and in dual GNSx30 installations you have to switch crossfill off to do that), worry about which waypoint to select, or even (bad idea) switch to a waypoint that is not on the procedure, as this will prevent the nav system from sequencing in to the missed approach.
Where it is dangerous is on non-precision approaches, because here the DME is the PRIMARY aid to identify the missed approach point and hence CRITICAL, not just some cross check. Again, the best way is to fly the GPS overlay, if the FAF and step-down fixes are in the database there is absolutely no point in making it up yourself.
Given the two above, it is easy to understand why the G1000 crowd in the cirrus could not care less about DME, and are probably right.
The only REAL danger exists for people who do not have overlay approaches, and make it up as they go along.
