Definition
An instrument approach that uses a standard Instrument Landing System for vertical and lateral guidance to the runway, while air traffic control monitors the aircraft's position with high-update-rate radar (Precision Runway Monitor) to allow simultaneous independent approaches to closely spaced parallel runways. The approach is conducted under specific procedures that include monitoring two communication frequencies and being prepared to execute an immediate breakout maneuver if another aircraft deviates toward the protected airspace.
Plain English
A normal ILS approach flown into airports where two parallel runways are close together. Special radar watches the planes on both runways closely, so two aircraft can land at the same time on different runways safely. Pilots must listen on two radios and be ready to turn away quickly if told.
Context Anchor
Seen on instrument approach charts, approach briefings, and air traffic control clearances at airports that use PRM procedures for simultaneous approaches.
Derivation
ILS = Instrument Landing System, the standard precision approach using a localizer for course and glideslope for descent. PRM = Precision Runway Monitor, named for the high-precision radar that monitors aircraft positions far more often than normal radar. Knowing PRM is about precise monitoring (not a different kind of approach) helps the term make sense.
Why Pilots Care
Enables higher landing rates at busy airports without compromising safety margins.
Grounding Statement
Picture two aircraft landing on nearby runways at the same time, with one crew flying the ILS and a controller watching both paths closely for any unsafe movement.
Intuition Check
Do not read PRM as just a more accurate ILS. The ILS gives the aircraft its approach guidance; PRM is the added monitoring and procedure that helps keep simultaneous approaches separated.
Example Sentence 1
Before accepting the ILS/PRM approach into runway 28R, the crew reviewed the breakout procedure and tuned the second radio to the monitor frequency.
Example Sentence 2
Pilots must be current in ILS/PRM procedures to accept this type of approach clearance.