Radar Services Notes

Radar Services

Chapter 8 Overview

Sajid Randhawa presents Chapter 8, focusing on radar services.

RADAR Definition

RADAR stands for Radio Detection And Ranging. It's a system that detects the presence, direction, distance, and speed of objects like aircraft and ships. This is achieved by sending out pulses of radio waves that reflect off the object and return to the source.

Radar System Capabilities

Radar systems used in air traffic services must have high reliability, availability, and integrity. Backup facilities are essential to prevent service interruptions due to system failures or degradations. A typical radar system includes:

  • Radar sensor(s)
  • Radar data transmission lines
  • Radar data processing system
  • Radar displays

These systems should display safety-related alerts and warnings, like conflict alerts, minimum safe altitude warnings, conflict prediction, and unintentionally duplicated SSR codes. Sharing radar information between adjacent control areas is encouraged to improve radar coverage.

PSR and SSR

Primary Surveillance Radar (PSR) and Secondary Surveillance Radar (SSR) can be used alone or in combination for air traffic services, including providing separation between aircraft. This is conditional on:

  • Reliable coverage in the area.
  • Satisfactory probability of detection, accuracy, and integrity of the radar system(s).
  • PSR systems should be used where SSR alone isn't sufficient for air traffic service requirements.

SSR systems, especially those with monopulse technology or Mode S, can be used independently for separation, provided that:

  • SSR transponders are mandatory in the area.
  • Aircraft identification is established and maintained using assigned discrete SSR codes.

Mono Pulse Technique

Mono pulse technique enables azimuth information of an SSR transponder aircraft to be derived from each pulse detection by comparing signals from two or more antenna beams. This technique improves azimuth resolution, reduces false reports from unsynchronized interrogator transmissions ('fruit'), and minimizes garbling compared to conventional SSR sensors.

Limitations and Information Publication

The use of radar in air traffic services is restricted to specified areas and is subject to limitations set by the ATS authority. Information on operating methods, practices, and equipment limitations that directly affect air traffic services must be published in aeronautical information publications.

Presentation of Radar Information

Radar-derived information displayed to controllers should include radar position indications, radar map information, and data from SSR Mode A, Mode C, and Mode S. The radar system must continuously update the presentation of radar-derived information, including radar position indications.

Radar Position Indications

Radar position indications can be displayed as:

  • Radar position symbols (RPS), including:
    • PSR symbols
    • SSR symbols
    • Combined PSR/SSR symbols
  • PSR blips
  • SSR responses

Distinct symbols should be used for:

  • Unintentionally duplicated SSR codes
  • Predicted positions for a non-updated track
  • Plot and track data

Reserved SSR codes like 7500 (hijacking), 7600 (communication failure), and 7700 (emergency), operation of IDENT, safety-related alerts and warnings, and automated coordination information must be presented clearly for easy recognition.

Communications

Communication systems must be highly reliable and available, with adequate backup facilities. Direct pilot-controller communications are required before providing radar services, unless emergencies dictate otherwise.

Provision of Radar Services

Radar-derived information, including safety alerts like conflict alert and minimum safe altitude warning, should be used to enhance safety, capacity, and efficiency in air traffic control.

Use of SSR Transponders

Pilots and controllers must follow published operating procedures strictly to ensure the safe and efficient use of SSR. Standard radiotelephony phraseology must be used, and correct transponder code settings must be maintained.

Radar Display Elements

A radar display includes elements such as aircraft beacon, aircraft callsign, altitude in thousands of feet, a symbol indicating the scope controlling the aircraft's tag, aircraft class (e.g., Heavy), ground speed in knots, and an indicator for automated handoffs. The 'raw radar' blip is shown separately from computer-generated text. An example shows: TEAM50, 3431, 060 H 21, and HND C66.

SSR Code Management

Codes 7700, 7600, and 7500 are reserved internationally for emergencies, radio communication failure, and unlawful interference, respectively. SSR codes are allocated based on regional air navigation agreements considering overlapping radar coverage. The ATS authority establishes a plan for code allocation to ATS units, compatible with adjacent states. A code should not be used for multiple functions within the same SSR coverage area for a set time. Code changes required of pilots should be minimized. Discrete codes are assigned to individual aircraft where identification is needed and should be retained throughout the flight when possible. SSR codes are reserved for exclusive use by medical aircraft operating in international armed conflict areas and are allocated by ICAO.

Level Information based on the use of Mode C

Verification of Accuracy of Mode C-Derived Level Information

The tolerance for Mode C-derived level information is \pm 60 m ( \pm 200 ft) in RVSM airspace and \pm 90 m ( \pm 300 ft) in other airspace. The ATS authority can specify a smaller criterion, but not less than \pm 60 m ( \pm 200 ft), for practical reasons.

Determination of Level Occupancy

The criterion to determine that a specific level is occupied by an aircraft is \pm 60 m ( \pm 200 ft) in RVSM airspace and \pm 90 m ( \pm 300 ft) in other airspace. The ATS authority can specify a smaller criterion, but not less than \pm 60 m ( \pm 200 ft), if more practical.

Aircraft Maintaining, Vacating, Passing and Reaching a Level

  • An aircraft maintaining its assigned level is within appropriate tolerances per SSR Mode C.
  • An aircraft vacating a level has commenced its maneuver when SSR Mode C indicates a change of more than 90 m (300 ft) from its previously assigned level in the anticipated direction.
  • An aircraft passing a level in climb or descent has crossed it when SSR Mode C shows it has passed the level by more than 90 m (300 ft) in the required direction.
  • An aircraft is considered to have reached the level to which it has been cleared when three consecutive renewals of Mode C-derived level information have indicated that it is within the appropriate tolerances of the assigned level Mode C refers to aircraft equipped with an altitude encoder and altimeter. With Mode C, ATC will actually see the flight level altitude on their radar screen if the transponder is operating in the Mode C or "ALT" (altitude) Mode.