Cobalt,
There are ILS approaches with step down fixes inside the FAF or at the MAP that are not in the database. In those instances, you need to fly the ILS the old fashioned way and use the GPS to reference the waypoint at the DME location.
Michael
I as are others as to how there could be any confusion between the GPS distance based on the NDB and no other radio aid used in the procedure ?
Do you undersand the issue ?
Aviathor.
Ref the LFAC 24 approachIf you have the aircraft capability and no DME from a human factors point of view it would be better to fly the RNAV LPV approach as it elliminates the risk of putting the wrong MK fix in the GPS and it gives the same minima as the ILS.
The GNS530W provides a data block under the Com & Nav frequency blocks giving the name, radial and distance to the VOR….however when tuned to a localizer I believe airport and rwy is given (my experience is with the 430W where there is no such data field)…. it would be easy for Garmin to use this field to display a calculated DME readout based on the tuned LOC frequency…. maybe the 650/750 does this already?
NCYankee wrote:
Of course, the US does not support DME offsets, so this is not an issue in the US.
So if I understand correctly, in the US there are none and never have been any published DME approaches where the DME station is not co-located on the airport ?
Conversely, there are N DME published approches in Europe where the DME station is NOT co-located on the airport ?
Is this the major difference that we are discussing ?
Michael wrote:
So if I understand correctly, in the US there are none and never have been any published DME approaches where the DME station is not co-located on the airport ?Conversely, there are N DME published approches in Europe where the DME station is NOT co-located on the airport ?
Is this the major difference that we are discussing ?
There are no DME’s in the US that report a fictitious distances, such as offsetting the true distance to the DME station such that it reads zero at the threshold. There are many approaches in the US that use off field DME, but these are associated with the VORTAC or VOR-DME facility of the same name in the database. Localizer DME’s are colocated at the Localizer antenna location and have the same name as the localizer ident in the database. So, in the US, if you use the appropriate name in the database, it will read identical to the real DME distance.
In most cases, the ILS approach can be loaded from the database and used for situational awareness, as all the needed waypoints are named. In some cases, particularly those that have step down fixes or missed approach points that are needed to fly the localizer only version of the approach, the DME locations may not be in the database. In that case, you can’t load the approach and have to use the DME name to determine the distance to these unnamed fixes. With a single GNS/GTN system, you have to fly the approach the old fashioned way, without a moving map overlaying the approach for situational awareness.
There are no DME’s in the US that report a fictitious distances, such as offsetting the true distance to the DME station such that it reads zero at the threshold
If you have a dme ils on both ends of a runway, do you have two dme stations?
Yes. Take KCLT as an example. It has 8 runway ends, 6 use a localizer-dme and the other two use the CLT VORTAC. There are a few airports that use the same frequency on both runway ends for the localizer, but only one set of antennas is connected to the transmitters at a time. This can lead to errors when the runways get switched around and the tower forgets to switch the ILS. Edit, when the same frequency is used, the ident is unique, but it is an easy mistake to make and not catch.
A_and_C wrote:
Ref the LFAC 24 approach
If you have the aircraft capability and no DME from a human factors point of view it would be better to fly the RNAV LPV approach as it elliminates the risk of putting the wrong MK fix in the GPS and it gives the same minima as the ILS.
I agree with that, and I will normally prefer the LNAV approach over an ILS without DME for that reason (don’t have WAAS/SBAS)
I just wanted to illustrate one of the pitfalls of DME substitution with a specific example.
Aviathor
You illustrated the DME substitution issue so well I find it difficult to understand how some on this forum seem unable to understand the human factors issues of this practice.
