Localizer-DME waypoints

Garmin has added localizer-DME waypoints to their GPS databases. That means pilots can use an IFR-certified GPS receiver in lieu of DME on all localizer, localizer back course, ILS, or any other localizer-type procedure that requires DME.

“FAA granted approval in 1998, but some localizer-type approaches were excluded.”

That’s because GPS databases put the airport waypoint at the center of the airport. DME transmitters are usually co-located with VORs or localizers, not at the airport center. Using fix distances from the airport waypoint would give a pilot inaccurate distance information for an instrument approach.

Garmin has added localizer-DME waypoints to their GPS databases. That means pilots can use an IFR-certified GPS receiver in lieu of DME on all localizer, localizer back course, ILS, or any other localizer-type procedure that requires DME.

It’s actually been legal even without these waypoints, so long as there is some other waypoint that could be used as a reference (so if, for instance, there was a named intersection that was also depicted as a DME distance, you could do the math and count up in distance from that named waypoint.) This was an addendum to the original GPS-substitutes-for-DME-and-ADF memo.

Having the DME location in the database does mean that it’s a whole lot easier and less error-prone though.