Radar
Definition
Radar (Radio Detection and Ranging) is a ground-based system used to detect, locate, and track aircraft by transmitting radio waves and analyzing their reflections. In air traffic control (ATC), radar enables real-time monitoring of aircraft position and movement, forming the backbone of surveillance and separation services.
Types of Radar
| Type | Name | Function |
|---|---|---|
| Primary Radar (PSR) | Passive detection | Measures position using reflected signals; detects any object (aircraft, terrain, birds) |
| Secondary Surveillance Radar (SSR) | Cooperative | Interrogates onboard transponders to receive aircraft ID, altitude, and other data |
| Monopulse Secondary Radar | High precision | Advanced SSR for Mode S tracking with higher accuracy |
Primary Radar (PSR)
- Does not rely on aircraft systems
- Detects any object reflecting the radar beam
- Provides azimuth (bearing) and distance, but no altitude or identity
- Used for military, backup, or non-cooperative target detection
- Susceptible to clutter (e.g., weather, terrain)
Secondary Radar (SSR)
- Requires aircraft to carry a transponder
- Provides aircraft identity (squawk) and pressure altitude (Mode C)
- With Mode S, also transmits heading, groundspeed, and callsign
- Allows target labeling on controller screens, improving clarity and response
Phraseology Examples
- “Radar contact” → ATC has identified your aircraft on radar
- “Resume own navigation” → Radar vectors are no longer provided
- “Radar service terminated” → Aircraft leaving radar coverage or switching to procedural control
Radar Vectoring
ATC can issue headings to aircraft for sequencing, separation, or traffic avoidance.
Typical instructions include:
- “Turn left heading 210”
- “Fly heading 060 for spacing”
Radar vectoring is common in approach and departure phases, especially in busy terminal areas.
Radar Identification Methods
- Squawk Ident → Controller instructs pilot to press IDENT button
- Position correlation → Controller matches position report with radar return
- SSR Code Assignment → ATC assigns a discrete squawk code, linked to flight plan
- Departure correlation → Known time and runway departure allows positive ID
Limitations of Radar
- Line of sight only: Radar coverage depends on aircraft altitude and terrain
- Not all airspace is radar-covered: Especially in mountainous or remote areas
- Radar separation minima must be maintained (e.g., 3–5 NM horizontally, 1,000 ft vertically)
Radar Services Provided
- Traffic sequencing and spacing
- Vectoring for approaches
- Weather avoidance guidance
- Conflict resolution advisories
- Transition between airspace sectors
Modern Developments
- Mode S radar networks support enhanced surveillance
- ADS-B and multilateration are augmenting or replacing radar in some FIRs
- Radar screen automation provides data tags showing callsign, level, speed, and intent
