Definition
A high-update-rate radar and display system used by air traffic control to monitor aircraft on simultaneous independent approaches to closely spaced parallel runways. It provides controllers with rapid position updates and automated alerts so that aircraft can be safely separated when conducting parallel instrument approaches in low visibility.
Plain English
A special radar that watches planes very closely as they line up for landing on two runways that sit close together side by side. Its quick updates let controllers safely keep two streams of aircraft landing at the same time, even when pilots can't see the other runway.
Context Anchor
Seen in approach control and instrument approach discussions at busy airports that use closely spaced parallel runways.
Derivation
Precision (from Latin praecisio, 'a cutting off') here means highly accurate. Monitor (from Latin monere, 'to warn') means a device that watches and warns. Together: a system that watches runway approaches with high accuracy and warns controllers of any deviation.
Why Pilots Care
It allows safe simultaneous landings on parallel runways, increasing airport capacity without reducing separation standards.
Grounding Statement
Picture two airplanes landing on parallel runways close together while controllers use a very fast radar display to make sure neither airplane drifts toward the other.
Intuition Check
Do not read “precision” as meaning the runway itself is unusually exact. Here it means the monitoring system gives controllers accurate, frequent position information.
Example Sentence 1
The Precision Runway Monitor allowed controllers to run simultaneous approaches to both parallel runways even though the ceiling was low.
Example Sentence 2
Pilots must be trained and equipped before flying approaches that use the Precision Runway Monitor at the destination airport.