Definition
A type of secondary surveillance radar that determines an aircraft's bearing using a single pulse return from the aircraft's transponder, rather than relying on multiple sweeps of a rotating beam. By comparing signals received simultaneously across different parts of its antenna, MSSR calculates the aircraft's position more accurately and updates faster than conventional secondary radar, which is why it is used in precision-critical applications such as Precision Runway Monitor (PRM) operations.
Plain English
A radar that figures out exactly where an aircraft is from just one reply from its transponder, instead of needing several sweeps. This makes it faster and more accurate, which matters when controllers are watching aircraft fly closely spaced parallel approaches.
Context Anchor
Seen in instrument flying discussions of PRM radar, where controllers need very accurate tracking of aircraft on closely spaced approach paths.
Derivation
Mono- comes from Greek for 'one' or 'single.' Pulse refers to the brief radio signal the radar uses. Together, 'monopulse' means the radar can extract position information from a single return pulse — the key feature that distinguishes it from older systems that needed multiple pulses to fix a target's location.
Why Pilots Care
Gives controllers precise real-time tracking so they can safely manage simultaneous approaches to parallel runways in instrument conditions.
Intuition Check
Secondary does not mean less important here. In radar, secondary means the system uses a reply from equipment on the aircraft instead of only bouncing a signal off the aircraft's body.
Example Sentence 1
The PRM system uses MSSR to track each aircraft's position with the precision needed for closely spaced parallel approaches.
Example Sentence 2
MSSR updates provided tighter spacing tolerances than conventional secondary radar.