ATC Systems and Radar Summary
ATC Systems Overview
Purpose: Locate and identify aircraft for ATC.
ATC Radar Systems
Types:
Primary Radar (PSR): Detects metallic structures; cluttered displays; provides bearing and range.
Secondary Surveillance Radar (SSR): Identifies specific aircraft via transponder responses.
SSR Modes
Modes:
Mode A: IDENT (4-digit octal code).
Mode C: Altitude information.
Mode S: Includes Mode A and C, plus unique 24-bit ICAO address for collision avoidance systems (TCAS/ADS).
Pulse Transmission
Pulse Spacing:
Mode A: 8 microseconds.
Modes C/T: 21 microseconds.
Framing Pulses: F1 and F2 used to identify legitimate replies; spaced 20.3 microseconds apart.
Side Lobe Suppression (SLS)
Prevents unwanted transponder responses; uses omnidirectional P2 pulse.
Special ATC Codes
Emergency Codes:
7700: Emergency (MAYDAY).
7600: Lost Communications.
7500: Hijack.
Avoid using 7000 series codes for general purposes.
FRUIT Issue
FRUIT: False Replies from Unsynchronized Transmissions.
Solution: Mode S with lockout protocol to reduce unnecessary replies.
DME and ATC Interface
Both systems operate on similar frequencies (L BAND); utilize suppression cables to prevent simultaneous transmissions.
ATC Systems Overview
Purpose: Locate and identify aircraft for ATC.
ATC Radar Systems
Types:
Primary Radar (PSR): Detects metallic structures; cluttered displays; provides bearing and range.
Secondary Surveillance Radar (SSR): Identifies specific aircraft via transponder responses.
SSR Modes
Modes:
Mode A: IDENT (4-digit octal code).
Mode C: Altitude information.
Mode S: Includes Mode A and C, plus unique 24-bit ICAO address for collision avoidance systems (TCAS/ADS).
Pulse Transmission
Pulse Spacing:
Mode A: 8 microseconds.
Modes C/T: 21 microseconds.
Framing Pulses: F1 and F2 used to identify legitimate replies; spaced 20.3 microseconds apart.
Side Lobe Suppression (SLS)
Prevents unwanted transponder responses; uses omnidirectional P2 pulse.
Special ATC Codes
Emergency Codes:
7700: Emergency (MAYDAY).
7600: Lost Communications.
7500: Hijack.
Avoid using 7000 series codes for general purposes.
FRUIT Issue
FRUIT: False Replies from Unsynchronized Transmissions.
Solution: Mode S with lockout protocol to reduce unnecessary replies.
DME and ATC Interface
Both systems operate on similar frequencies (L BAND); utilize suppression cables to prevent simultaneous transmissions.
Summary
This note provides an overview of Air Traffic Control (ATC) systems, focusing on how aircraft are located and identified. It details two main types of radar: Primary Radar (PSR), which detects metallic structures, and Secondary Surveillance Radar (SSR), which identifies aircraft via transponder replies. SSR Modes include Mode A for identification codes, Mode C for altitude, and Mode S for a comprehensive display of identification and altitude, along with a unique ICAO address for collision avoidance. The note also covers pulse transmission specifications like Pulse Spacing for different modes and the role of Framing Pulses. Key operational aspects such as Side Lobe Suppression (SLS) to prevent unwanted transponder responses and special Emergency Codes (7700, 7600, 7500) are highlighted. The FRUIT issue (False Replies from Unsynchronized Transmissions) and its solution via Mode S are explained. Finally, the interaction between DME and ATC systems sharing L-BAND frequencies is mentioned.
Review of Bolded Terms for Test
Here's a review of the bolded terms that will be on the test:
Types: Refers to the categories of ATC radar systems:
Primary Radar (PSR): A radar system that detects aircraft by sending out a signal and receiving the reflection from the aircraft's metallic structure. It provides bearing and range but can result in cluttered displays.
Secondary Surveillance Radar (SSR): A cooperative radar system that identifies specific aircraft by interrogating their transponders, which then send back coded responses.
Modes: Refers to the different operational modes of Secondary Surveillance Radar (SSR):
Mode A: An SSR mode that provides a 4-digit octal identification code (IDENT) for the aircraft.
Mode C: An SSR mode that provides altitude information from the aircraft's transponder.
Mode S: An advanced SSR mode that includes Mode A and C capabilities, along with a unique 24-bit ICAO address for the aircraft, enabling advanced features like collision avoidance (TCAS/ADS).
Pulse Spacing: The specific time interval between pulses transmitted by the ATC interrogator to differentiate between various transponder modes. Mode A uses 8 microseconds, while Modes C/T use 21 microseconds.
Framing Pulses: Pulses designated as F1 and F2, spaced 20.3 microseconds apart, used by the transponder to identify and validate legitimate interrogation replies.
Side Lobe Suppression (SLS): A technique used to prevent aircraft transponders from replying to interrogation pulses transmitted through the minor lobes of the antenna pattern, ensuring replies only come from the main lobe. It uses an omnidirectional P2 pulse.
Emergency Codes: Special 4-digit octal transponder codes reserved for specific emergency situations:
7700: General Emergency (MAYDAY).
7600: Lost Communications.
7500: Hijack.
FRUIT: An acronym for False Replies from Unsynchronized Transmissions, which refers to unwanted replies received by an interrogator from transponders that were triggered by other interrogators. Mode S with its lockout protocol is a solution to this issue.