Pilot's Tip of the Week

Transponder On During Taxi?

Featuring John Krug

Subscriber Question:

"Should I have my transponder turned on, off, or on standby during ground operations? I've heard different opinions on this." - Nicholas B.

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"Several years ago, the FAA changed the guidance in the AIM. The current guidance to pilots is:

Civil and military transponders should be turned to the on or normal altitude reporting position prior to moving on the airport surface to ensure the aircraft is visible to ATC surveillance systems.

Transponder_On_Taxi_UPDATED.pngThe FAA has installed ground radar surveillance systems at many large air carrier airports. These systems rely on information from the aircraft's transponder and discrete beacon code to identify the aircraft as it is moving on the surface. Some airports will note in the chart supplement remarks such as ASDE X surveillance system in use, pilots should operate transponders with Mode C on all taxiways and runways.

Controllers in the tower see this information presented as a color display of aircraft and vehicle positions overlaid on a map of the airport's runways, taxiways and approach corridors. The system essentially creates a continuously updated map of all airport surface operations that controllers can use to spot potential collisions.

Since you may not know whether you are operating at an airport with a ground surveillance system, good operating practice is to leave the transponder on at all times.

Additionally, if you have ADS-B Out and the appropriate receiver, you'll see on your display all transponder equipped aircraft taxiing on the ground. The targets are color coded depending on whether they are on the ground or airborne. If you turn off your transponder (or select standby) on the ground, other aircraft will not see your return.

Formerly there was a concern that with older radar systems, transponder operation on the ground could cause interference and multiple targets on the radar display. Modern digital systems can filter out transponders close to the antenna."

Next week's tip: Minimum Controllable Airspeed 

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