Definition
An instrument approach that uses an LDA (a localizer-type course offset from the runway centerline by up to about 3 degrees) combined with Precision Runway Monitor radar to allow simultaneous independent approaches to closely spaced parallel runways. It is one of the two paired approaches used in a Simultaneous Offset Instrument Approach (SOIA) operation, where one aircraft flies the LDA/PRM to one runway while another flies an ILS/PRM or RNAV/PRM to the adjacent parallel runway. The offset course keeps the two aircraft laterally separated until the LDA pilot acquires the other traffic visually and continues to landing under visual conditions.
Plain English
An approach where you fly a course aimed slightly to one side of the runway (not straight in) while controllers use high-update radar to watch you and another aircraft landing on a nearby parallel runway at the same time. Near the end, you must see the other aircraft and the runway, then sidestep visually to land.
Context Anchor
Seen on instrument approach charts and in ATC clearances for simultaneous offset instrument approaches to closely spaced parallel runways.
Derivation
LDA stands for Localizer-type Directional Aid, a localizer signal that isn't aligned with a runway centerline. PRM stands for Precision Runway Monitor, the high-update-rate radar system controllers use to monitor parallel approaches. The combination name signals both pieces: the offset course you fly and the radar service watching you fly it.
Why Pilots Care
Increases landing capacity at major airports without reducing safety margins during simultaneous arrivals.
Grounding Statement
Picture two aircraft approaching parallel runways at the same time, with one aircraft flying a slightly offset electronic path so both can remain safely separated.
Intuition Check
Do not assume LDA/PRM means a normal straight-in localizer approach. The LDA course may be offset from the runway, and the PRM part means ATC is using special monitoring for simultaneous parallel approaches.
Example Sentence 1
Cleared for the LDA/PRM Runway 28L approach into San Francisco, the crew tuned the second radio to the PRM monitor frequency and reviewed the breakout procedure.
Example Sentence 2
Training for LDA/PRM approaches prepares pilots for high-density operations at airports like San Francisco International.