Turn it on for safety: using transponders on aircraft

Most aircraft today have transponders, yet many pilots don’t turn them on. Remembering to use this piece of equipment could save your life and the lives of many others.

Just before takeoff, always “turn it on for safety.”

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Why turn on your transponder

There are two good reasons to turn your transponder on while in the air.

  1. Air traffic control is able to “see” all aircraft with their transponders on. This allows air traffic controllers to pass on conflicting traffic information. If your transponder is able to reply on Mode C (automatic altitude reporting), controllers can figure out more easily where potential conflicts could happen in the sky.
  2. Aircraft (usually commercial and corporate aircraft) with a traffic alert and collision avoidance system (TCAS) are able to detect all other aircraft with working transponders. TCAS-equipped aircraft will detect your aircraft and, if your transponder can report altitude, will avoid colliding with you.

How to adjust your transponder

Adjust your transponder as air traffic control instructs.

In the absence of air traffic control instructions, adjust as follows:

  • Visual flight rules (VFR) at or below 12,500 feet above sea level (ASL): Mode A, Code 1200, plus Mode C
  • VFR above 12,500 feet ASL: Mode A, Code 1400, plus Mode C
  • Instrument flight rules (IFR) in low-level airspace: Mode A, Code 1000, plus Mode C
  • IFR in high-level airspace: Mode A, Code 2000, plus Mode C

International Civil Aviation Organization (ICAO) terminology

Transport Canada and the ICAO use different terms to talk about transponders.

  • TCAS II, version 7, is what ICAO refers to as “ACAS II”
  • ICAO refers to this system as an “airborne collision avoidance system” (ACAS)
  • ICAO uses the term “traffic advisory” and not “traffic alert”

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