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1.2 Surveillance Types

1.2.1 General

Surveillance systems provide the Approach Controller with information on aircraft position, identity, and altitude.

The Approach Controller shall understand the capabilities and limitations of each surveillance type and apply them appropriately.

1.2.2 Primary Surveillance Radar (PSR)

Primary Surveillance Radar (PSR) detects aircraft by transmitting radio signals and receiving reflections from the aircraft.

Characteristics

  • Does not require aircraft equipment
  • Provides position in terms of range and bearing
  • Does not provide identification or altitude information

Controller Use

PSR may be used to:

  • Observe aircraft position
  • Monitor unidentified or non-transponder aircraft
  • Provide basic surveillance in the absence of SSR

The Approach Controller shall not assume aircraft identity or altitude when using PSR alone.

1.2.3 Secondary Surveillance Radar (SSR)

Secondary Surveillance Radar (SSR) relies on aircraft transponders to provide enhanced information.

Modes

  • Mode A – Aircraft identification (squawk code)
  • Mode C – Pressure altitude
  • Mode S – Enhanced data (including aircraft identity and additional parameters)

Advantages

  • Provides positive identification (when validated)
  • Provides altitude information
  • Improves surveillance accuracy and reliability

Controller Use

The Approach Controller shall use SSR to:

  • Identify aircraft
  • Verify altitude information
  • Monitor compliance with clearances
  • Apply radar separation

1.2.4 Mode C and Altitude Verification

The Approach Controller shall verify Mode C altitude prior to using it for separation.

The controller shall:

  • Compare reported altitude with Mode C readout
  • Ensure accuracy within acceptable limits

If Mode C is unreliable or unavailable, the controller shall not use it for separation.

1.2.5 Mode S

Mode S provides enhanced surveillance capability.

Where available, the Approach Controller may use Mode S to:

  • Confirm aircraft identity
  • Access additional aircraft data
  • Improve situational awareness

Use of Mode S shall not replace standard identification procedures unless authorised.

1.2.6 Limitations of Surveillance

The Approach Controller shall be aware of surveillance limitations, including:

  • Radar coverage gaps
  • Clutter or interference
  • Transponder failures
  • Incorrect or unreliable altitude readouts

Where surveillance reliability is degraded, the controller shall apply alternative control methods.

1.2.7 Key Principle

Surveillance information shall be used to support safe and accurate control.

The Approach Controller shall:

  • Verify information before use
  • Understand system limitations
  • Avoid assumptions regarding aircraft identity or altitude