Definition
An instrument approach that uses a Localizer-Type Directional Aid (LDA) for lateral guidance combined with Distance Measuring Equipment (DME) to provide the pilot with slant-range distance information to a specific reference point on the airport. The LDA provides course guidance similar to an ILS localizer but is not aligned within 3 degrees of the runway, and DME replaces the need for timing or fixes derived from other navaids to identify approach segments and the missed approach point.
Plain English
An approach that gives you a narrow course to follow toward the airport, plus a continuous readout of how far you are from a fixed point on the field. The course is not lined up straight with the runway, so you fly the course down, then maneuver to land.
Context Anchor
Seen on instrument approach charts and equipment requirement notes, especially when checking whether the airplane has the working navigation equipment needed for that approach.
Derivation
Localizer-Type Directional Aid means it works like a localizer (a narrow radio course) but is treated as a directional aid because it isn't aligned closely enough with the runway to be a true ILS. Distance Measuring Equipment is the airborne and ground system that measures how far the aircraft is from the station. Combined, the name tells you exactly what's available: LDA course guidance plus DME distance.
Why Pilots Care
Determines whether an approach can continue safely or requires higher minimums when one of the navigation aids becomes unavailable.
Intuition Check
Do not assume LDA/DME is the same as ILS. It can give precise left-right guidance, but it does not automatically provide the full runway-aligned guidance of an ILS.
Example Sentence 1
The crew briefed the LDA/DME approach into Roanoke, noting the offset course would require a visual maneuver to align with the runway after breaking out.
Example Sentence 2
With the DME inoperative on the LDA/DME approach, the pilot climbed to the published higher minimums.