# Is it recommended to have an ADS-B transponder in ALT mode on the ground? [duplicate]

Early on in training I was told that unless the airport specifically noted it on the chart, that the transponder was turned to ALT (altitude) mode just prior to taking the runway for take-off (lights, camera, action), and was changed back to SBY (standby) immediately after exiting the runway.

Recently we had a Garmin GTX-345 ADS-B transponder installed in our aircraft and as part of the ADS-B rebate program you need to do a check-out in "rule airspace". When I got the test report from the FAA I noticed that I passed the air portion but failed the ground portion due to an insufficient number of reports (messages) while on the ground. I retook the test making sure to put the transponder in ALT mode at the hangar and subsequently passed.

This leads me to believe that the transponder should be in ALT mode pretty much all the time. Is there any recommendations from the FAA that say that ADS-B transponders should be active while on the ground?

The GTX-345 Manual (2-1) has this to say:

The transponder system no longer supports a pilot selectable GND mode. The transponder should always be in ALT mode prior to moving on the airport surface. It must be in ALT mode when operating in certain controlled airspace, in accordance with 14 CFR 91.215. For guidance on transponder operation, refer to the FAA Aeronautical Information Manual (AIM), 4-1-20(a)(3)

(Emphasis mine)
Is this backed up by the FAA?

## marked as duplicate by Lnafziger, mins, Pondlife, SMS von der Tann, Ron BeyerApr 14 '17 at 23:38

• @RalphJ Actually, no. The answer is the same and it doesn't matter if you have ADS-B or not. The transponder should be on and in ALT mode on while taxiing regardless. Ron even starts off his question telling us how he was taught (which is now superseded with new guidance) and his quote references the same guidance that applies to both. – Lnafziger Apr 14 '17 at 18:39

• I'd upvote the answer again just for that comment if I could :). 92.215 reads like all transponders must be in ALT mode while operating on the surface, which leads me to think that my training was incorrect in having it in SBY during taxi, but then again why would an airport like MKE have a comment that reads like this: ASDE-X IN USE. OPERATE TRANSPONDERS WITH ALTITUDE REPORTING MODE AND ADS-B (IF EQUIPPED) ENABLED ON ALL TWYS AND RYS.? – Ron Beyer Apr 14 '17 at 16:32