Definition
Precision Runway Monitor (PRM) is a high-update-rate radar and controller display system used by ATC to monitor simultaneous independent approaches to closely spaced parallel runways. It allows aircraft to fly RNAV (area navigation) approaches to parallel runways whose centerlines are spaced closer than would otherwise permit independent operations, by giving controllers fast, precise position updates and dedicated monitoring of the No Transgression Zone between the final approach courses.
Plain English
PRM is a special radar and monitoring setup that lets two airplanes land at the same time on parallel runways that are very close together. It updates aircraft positions much faster than normal radar so controllers can spot any drift toward the other aircraft's path immediately and issue a breakout if needed.
Context Anchor
You may see this on an instrument approach chart or hear it during air traffic control instructions for parallel runway arrivals at busy airports.
Derivation
Precision = exact or fine-grained. Runway Monitor = the system watches aircraft on final approach to specific runways. The name describes its job: precisely monitoring runway approaches in real time.
Why Pilots Care
Enables safe, simultaneous landings on parallel runways, increasing airport capacity without compromising separation.
Intuition Check
Do not read PRM as just another label on an approach chart. Here it signals a closely watched parallel-runway operation where staying on the assigned path is especially important.
Example Sentence 1
Cleared for the RNAV PRM approach to runway 28R, the crew tuned the monitor frequency in their second radio and briefed the breakout procedure.
Example Sentence 2
Because the runways are only 3,400 feet apart, the tower required PRM monitoring for the entire approach.