Air Traffic Surveillance

Reference AIM COM 7.0

Recall: RADAR = RAdio Detection and Ranging (i.e. what's out there, which direction, and how far away?)

Primary Returns

• computes target positions by determining range and azimuth of reflected radio frequency energy
• passive - does not rely on info from aircraft
• uses:
• TSR (terminal surveillance radar) - short range (80 NM) to complement SSR
• PAR (Precision Approach Radar) - approach aid
• ASDE (Airport Surface Detection Equipment) - high def for aircraft and vehicles on manoeuvring areas
• Weather Radar - monitor hazardous weather conditions

Secondary Returns

• determines aircraft range by measuring the interval between transmitting an interrogation to and receiving a reply from an airborne transponder
• uses:
• enroute control - long range (200 NM)
• terminal control - in conjunction with PSR

ADS-B (Automatic Dependent Surveillance - Broadcast)

• uses aircraft avionics, satellites and/or ground infrastructure to relay a range of aircraft parameters to ATC
• automatic (no external stimulus required) but dependent (relies on aircraft avionics)

Traffic Alert and Collision Avoidance System (TCAS)

Reference AIM RAC 12.16

TCAS uses transponder interrogation and return signals to determine if aircraft around you pose a threat.  In order to detect these aircraft, they must be equipped with an operating Mode A, C, or S transponder.  Note: Mode A transponders will provide range and bearing only - no altitude info.

TCAS I provides TAs only.  
TCAS II provides TAs and RAs.

Some notes:

• Traffic Advisories (TAs) and Resolution Advisories (RAs) are only provided in the vertical plane (azimuth information is not reliably accurate)
• pilots should only alter their flight in the event of a RA (not a TA).  
• notify ATC ASAP of any deviation from your clearance.  Also notify them when you are clear of the conflict and returning to the cleared altitude
• See also CAR 602.31 (3) and (4) Compliance with ATC instructions and clearances

AIM RAC 12.16.6 (a) "Although TCAS will never be a complete substitute for a good lookout, good situational awareness and proper radio procedures, it has been proven to be a valuable tool in providing information on potential collision hazards."