Mode C on the ground?


#1

Throughout my training, I was always told to switch the transponder to “standby” on the ground, however I am noticing more and more airports that request the transponder be left on at all times while on the ground.

Also, I have heard that ATC radar generally filters out transponder replies from ground level on or near airports.

So, is there any reason why I should not just leave the transponder on “Alt” all the time? Any controllers out there care to comment?

–Dan


#2

More and more larger airports are getting ground radar that, unlike the old ground radar, uses transponders to identify aircraft.


#3

The larger airports are using ASDE, which is a grounding tracking radar. This is to assist ground control and to help prevent runway incursions. You transponder must be activated when on the ground at these airports.


#4

So, basically then leaving in on “Alt” mode is fine everywhere?


#5

At airports that have it noted in the remarks section, yes. The reason for requiring the Mode C is so the ground radar can tell the difference between ground and air traffic. Airports without the ASDE radar may still want you to shut off your transponder.


#6

Unless ATC tells you to Squawk Standby leave it on. I have never put a transponder on standby. Also remember most airports DO NOT have radar on the field so they won’t see your transponder anyway.

Frank Holbert
160knots.com