Peter, every DME station is in the database of the GNS430/GTN650 or similar .... and you can make a direct to any of these stations on your second GPS. Or what do you mean?
Ok, Nobbi. I will then also have enough money to buy a DME. I really thought about it ... butthen I decided to postpone it and rather buy the DFC90 autopilot. Which adds more to the safety!
Jason, the difference between the slant range and the GPS distance is so little, forget it!
On approach yes, but offsets can be large.
The issue is not the (very small) difference between GPS DCT reading and the DME slant range.
The issue is that there are many approaches where the DME stepdowns are based on a DME reading which is nothing to do with any point that corresponds to any point in the GPS database at which the DME will read zero.
I can't look it up easily but I recall the KCHD VOR approach for example uses a DME to some far away VOR. Can this be emulated with a GPS? I suppose it could if one can be sure the DME at that VOR is set to read zero at the VOR, and not with an offset rigged to read zero at the MAP.
What do you mean? If you have a direct to the physical DME station then there is no offset
The ILS/DME to Oxford uses I-OXF which is zero ranged to the threshold. If you use the GPS waypoint at the threshold it will not show zero.
If you have a direct to the physical DME station then there is no offset
There are loads of physical DMEs, used on approaches, which are rigged to read a nonzero value at the beacon.
The fact doesn't have to be published. The approach plate merely needs to publish the DME reading for each stepdown fix (or whatever).
Peter, not sure what you mean, have to think about that. If the physical VOR/DME station is in the database then a direct to it should be precise ... but maybe I don't understand. At all airporst I have flown to it worked (but that's only 5 IFR airports in the Cirrus ;-))
I do it different anyway. I have the ILS on the MFD with my active position and the vertical profile and I make a altitude check at the FAF, OM ...
