Definition
An ILS configuration in which the Distance Measuring Equipment (DME) transponder is installed at the same site as the Glide Slope (GS) transmitter, located near the runway touchdown zone. In this arrangement, the DME provides slant-range distance from the touchdown area rather than from the runway threshold or the localizer antenna at the far end of the runway. Distance readouts on approach charts using this configuration reference the GS/DME site.
Plain English
The distance-measuring radio is placed at the same spot as the glide slope antenna, which sits beside the runway near where aircraft touch down. So the DME tells you how far you are from the touchdown zone, not from the end of the runway.
Context Anchor
Seen in ILS approach descriptions, approach charts, and instrument procedures that use DME for distance information on final approach.
Derivation
Collocated comes from the Latin com- (together) and locare (to place), meaning 'placed together at the same location.' It signals that two pieces of equipment share a single site rather than being at separate ends of the runway.
Why Pilots Care
Gives accurate distance to decision altitude or missed-approach point, allowing correct timing of altitude checks and configuration changes during the approach.
Intuition Check
Collocated does not mean the DME is inside the glide slope transmitter. It means the DME ground equipment is installed at the same site or at a closely associated site, so the distance reading is tied to that location.
Example Sentence 1
Because the DME was collocated with the GS transmitter, the 1.0 DME readout corresponded to a position near the runway touchdown zone.
Example Sentence 2
With the DME collocated with the GS transmitter, the distance to the runway threshold was slightly greater than the DME indication until passing the antenna.