Definition
A high-update-rate radar surveillance system used by air traffic control to monitor independent simultaneous instrument approaches to closely spaced parallel runways. The PRM updates aircraft position much faster than standard radar and displays a no-transgression zone between the parallel approach paths, allowing controllers to detect and respond to any aircraft drifting toward the adjacent approach in time to issue a breakout instruction.
Plain English
A special fast-updating radar that lets controllers safely run two landing streams at the same time on parallel runways that are close together. It refreshes quickly enough that if one aircraft starts drifting toward the other approach, the controller can catch it and turn that aircraft away before the two get too close.
Context Anchor
You may see PRM in approach procedure titles, airport briefings, and air traffic control information for airports with closely spaced parallel runways.
Derivation
Precision = exact, finely measured. Runway Monitor = the system watches aircraft on final approach to runways. The 'precision' part refers to the radar's ability to track position more precisely and more frequently than standard surveillance radar, which is what makes simultaneous close-parallel approaches safe.
Why Pilots Care
Allows airports to conduct more simultaneous landings safely, increasing capacity without requiring wider runway spacing.
Grounding Statement
PRM helps controllers quickly see if an aircraft is drifting toward the space needed for another aircraft on a nearby parallel approach.
Intuition Check
PRM is not a navigation aid that the pilot uses to steer the airplane. It is mainly a controller monitoring system used to support certain simultaneous approaches.
Example Sentence 1
Approaching a major hub with closely spaced parallel runways, the crew briefed the ILS PRM approach and tuned the monitor frequency in their second radio.
Example Sentence 2
Pilots on PRM approaches must be prepared to execute a missed approach if directed by the controller.