Substitute DME for GPS?

Some certifiec IFR approach GPS units don't contain the localizer as a
waypoint, so you can't get the LOC distance (required for some LOC/ILS
approaches) directly.

"C J Campbell" wrote in message
...

"Thomas Borchert" wrote in message
...
Hi all,

a question that has probably been asked before, but I couldn't find it
in Google:

Is it allowed to use an IFR-approach-certified GPS instead of a DME in
a LOC-DME or VOR-DME approach that does not have a GPS-overlay?


I have never seen an approach certified GPS that did not have all the
intermediate waypoints for flying such an approach stored in its database.
Instead of your having to figure out that XYZZY is 5 DME from the airport,
the GPS should be giving you distance to XYZZY directly, automatically
cycling to the next waypoint upon reaching XYZZY. At least, that is what
the
Garmin and Bendix-King GPSs that I am familiar with do.

AIM does say that approach certified GPS may be used in lieu of DME for
approaches.

Mick Ruthven wrote:
Some certifiec IFR approach GPS units don't contain the localizer as a
waypoint, so you can't get the LOC distance (required for some LOC/ILS
approaches) directly.

Which ones don't have the localizer as a waypoint?

Dave Butler wrote in message ...
Mick Ruthven wrote:
Some certifiec IFR approach GPS units don't contain the localizer as a
waypoint, so you can't get the LOC distance (required for some LOC/ILS
approaches) directly.

Which ones don't have the localizer as a waypoint?

The Northstar M3 Approach, for one.

One is the Trimble Approach 2000 GPS.

"Dave Butler" wrote in message
...
Mick Ruthven wrote:
Some certifiec IFR approach GPS units don't contain the localizer as a
waypoint, so you can't get the LOC distance (required for some LOC/ILS
approaches) directly.

Which ones don't have the localizer as a waypoint?

C J Campbell wrote:
"Thomas Borchert" wrote in message
...

Hi all,

a question that has probably been asked before, but I couldn't find it
in Google:

Is it allowed to use an IFR-approach-certified GPS instead of a DME in
a LOC-DME or VOR-DME approach that does not have a GPS-overlay?



I have never seen an approach certified GPS that did not have all the
intermediate waypoints for flying such an approach stored in its database.

That may be the case but my GPS is not approach certified, it is
terminal and enroute only and does not have the localizer shack as a
waypoint. Therefore I would have to use the OM(or other intersection)
as a waypoint and use the little numbers on the chart.



AIM does say that approach certified GPS may be used in lieu of DME for
approaches.

The GPS does not have to be approach certified, terminal/enroute works too.

Newps wrote:
That may be the case but my GPS is not approach certified, it is
terminal and enroute only and does not have the localizer shack as a
waypoint. Therefore I would have to use the OM(or other intersection)
as a waypoint and use the little numbers on the chart.

The DME ground station may not even be in "the localizer shack". On
runways with ILS's at both ends, it's common to only have a single DME
ground station at one end of the runway.

For example, look at the profile view for the HPN ILS-34
(http://www.myairplane.com/databases/...s/00651I34.PDF). The
MAP is 0.6 miles from the threshold, but 1.8 DME. The reason is that
the DME is near the approach end of 16, a mile away from the 34
threshold.

There's no reason to have another one at the other end; both localizers
are on the same frequency (hence the paired DME freqs are the same), and
the DME station is omnidirectional.

The lat/long for airports is called the ARP (airport reference point),
usually located near the geographic center of the field. The localizer
is at the far end of the runway. If the approach calls for a DME from
the localizer, you cannot use GPS because there is no coordinate for
the localizer antenna array. Note that for a long runway, like the
11,500 foot long runways at KPIT, it could be more than a mile from
the end of the runway to the ARP.

The FAA is working to determine coordinates for these antennas, I have
heard.

Otherwise, your GPS will be more accurate than regular DME for VOR.

In article ,
(John Hamilton) wrote:

The lat/long for airports is called the ARP (airport reference point),
usually located near the geographic center of the field. The localizer
is at the far end of the runway. If the approach calls for a DME from
the localizer, you cannot use GPS because there is no coordinate for
the localizer antenna array. Note that for a long runway, like the
11,500 foot long runways at KPIT, it could be more than a mile from
the end of the runway to the ARP.

The FAA is working to determine coordinates for these antennas, I have
heard.

I find it hard to believe that the FAA doesn't know the location of the
localizer antennas down to the fraction of an RCH. Getting that
information published in databases may be a project, but I gotta believe
the information already exists somewhere inside the FAA.

"Roy Smith" wrote in message
...

I find it hard to believe that the FAA doesn't know the location of the
localizer antennas down to the fraction of an RCH. Getting that
information published in databases may be a project, but I gotta believe
the information already exists somewhere inside the FAA.


They appear on Obstruction Charts, but not every airport has an Obstruction
Chart, nor are they readily available.

However, it's not the location of the localizer array that's needed, it's
the location of the DME antenna. The DME is channelized to the localizer
frequency, but the DME is not collocated with a localizer similar to a
VORTAC. The DME antenna associated with a localizer frequency is generally
located near the "localizer shack" which is offset a few hundred feet to the
side of the localizer course. The locations of these DME antennas could
easily be published in the A/FD just as other navaids are.

There's an expression I haven't heard in more than 20 years.

Roy Smith wrote:
I find it hard to believe that the FAA doesn't know the location of the
localizer antennas down to the fraction of an RCH.