Transcript Transponders - Midland Gliding Club

Transponder Basics
Phil King,
Herefordshire Gliding Club
Overview
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Secondary Surveillance Radar
Mode A
Mode A/C
Mode S (selective)
Mode S/ES (extended squitter)
ADS-B (Automatic Dependent Surveillance
Broadcast)
• STCA (Short Term Conflict Alert)
• TCAS (Traffic alert Collision Avoidance System)
• Flarm
Acronyms
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ACAS – Airborne Collision Avoidance System
ADS-B – Automatic Dependent Surveillance Broadcast
CAT – Commercial Air Traffic
EHS – (Mode S) Enhanced Surveillance
ELS – (Mode S) Elementary Surveillance
ES – Extended Squitter
GA – General Aviation
LAST – Light Aviation SSR Transponder
LPST – Low Power SSR Mode-S Transponder
SSR – Secondary Surveillance Radar
STCA – Short Term Conflict Alert
TCAS – Traffic alert Collision Avoidance System
TMZ – Transponder Mandatory Zone
TRA(G) – Temporary Reserved Areas (Gliders)
UAV – Unmanned Aerial Vehicle
Secondary Surveillance Radar
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Primary radar relies on passive reflection
Secondary radar co-located with primary
SSR beam interrogates transponders
Transponder reply depends on its mode
ATC computers use SSR to tag primary
echoes with identifier and height
Mode A
• Developed from 2nd World War IFF
(Identification Friend or Foe)
• Limited number of squawk codes (4096)
• Non-selective – all transponders respond
to every interrogation broadcast
• Typically high power requirements:
– Frequent transmissions
– Power hungry transmitter
Mode A/C
• Incorporates mode A … plus …
• Altitude (i.e. Flight Level) as well as
identifier
• Extra power required to heat the altimeter
to a constant temperature
Mode S (selective)
• Incorporates mode A/C ability … plus …
• Less power required because:
– Transmitter is typically more efficient
– Altimeter does not need a heater
• Can respond selectively:
– If the SSR interrogates selectively
– Can reduce power even more
• Two levels of function (and price!):
– ELS: Elementary Surveillance (gliders & light aircraft)
– EHS: Enhanced Surveillance (for CAT)
Mode S/ES (extended squitter)
• As for mode S plus …
• Periodically broadcasts GPS position &
velocity
• Potentially provides one half of an airborne
collision avoidance system
• Provides some interoperability with ADS-B
ADS-B
• Broadly equivalent to Mode S/ES
• 150 mile range
• Does not need a ground-based radar
system
• Already in use in Alaska & Australia
• Arguably the system of the future
STCA (Short Term Conflict Alert)
• Automated system which alerts ATC
• Requires transponders on both aircraft
• Requires at least one aircraft to be in
contact with ATC
TCAS (Traffic alert Collision
Avoidance System)
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Is an Airborne Collision Avoidance System
Receives transponder signals
Works with mode A/C, S, or S/ES
Mandatory for CAT
Useless at detecting non-transponder
aircraft
Flarm
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Good value collision avoidance
11,000 in use
High take up in the Alps and Germany
Growing take up in UK
Short range (a few kilometres)
Ideal for gliders and slow speed aircraft
May be unsuitable for ATC or CAT
Unacceptable as an alternative to mode S
The End