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STANDARDTRANSPONDERCODES
• 1200Civil VFR flights inClass E or G airspace.
• 2000Civil IFR flights inClassG airspace.
• 3000Civil flights inA, C andD airspace, or IFR flights inClass E airspace.
• 6000Military flights inClassG airspace.
• 7500Unlawful interference.
• 7600Communications failure.
• 7700Emergency.
Some important points in transponder operation
• Select standby (STBY) before changing codes otherwise there is the real
possibility of transmitting a non-authorised code during the process.
• Donot press the IDENT feature unless requested byATS. ‘Squawk’ does
notmean press the IDENT. ‘Squawk IDENT’ is the request used for this
purpose.
• ‘Squawk STBY’means switch to theSTBY position.
• ‘Squawk 5632’ for example,means select STBY, then select code5632,
then squawkALT.
• Transponders require awarmup before being selectedON or ALT.
TheSTBY position is used towarmup the transponder.
• In the TEST position the reply light should comeonwhile the selector is
held in this position.
• The reply light comes on each time the transponder responds to an
interrogation. Thismay be from groundbased secondary radar or from a
nearby TCAS equipped aircraft.
• In theON position no altitude information is being transmitted.
• On occasions transpondersmay require ‘recycling’ to restore correct
encoding. To recycle, briefly select STBY then return toALT.
Information on the operation of transponders in theATCRADAR environment
is given inSection 3 ‘ATS surveillance services’ (page224).
1 — radar transponders
transponder operation