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IFR knowledge

4.74.2 Operation of Transponders

1. OFF

Transponder is OFF

2. SBY
  • Transponder is on STANDBY
  • is ON but will not respond to interrogation
  • Select just before take-off or as soon as practical after landing.
3. ON
  • Transponder is ON
  • Will reply to interrogations but Mode A only so altitude information not sent
4. ALT
  • Means 'altitude'
  • Transponder is ON and will reply to interrogation
  • Will transit mode A and mode C -
  • Normally used when airborne.
5. TST
  • This is the Transponder Test Function
6. IDENT
  • Causes the aircraft radar symbol on the screen to flash
  • Only push this when instructed to "SQUAWK IDENT" by controller