My ADS-B Out unit (and EchoUAT), is broken, (wifi out) and I need to send it back to be repaired/replaced. While it is out, I will only have a legacy Transponder with Mode-C.

Can I fly over (above) class bravo airspace? What about under the depicted airspace shelves, inside the Class Bravo 30nm ring but below the minimum altitude depicted on the chart for the shelf I am under?

The documentation I have found on the internet does not make it clear that I need both systems (Mode-C and ADS-B, or just one or the other to be compliant inside the Mode-C Veil.

If I need both, then I need to avoid the 30 nm ring completely, at any altitude. and while the box is being repaired I cannot fly to or from any airports under the Bravo airspace shelves.


2 Answers 2


14 CFR 91.225(d):

After January 1, 2020, except as prohibited in paragraph (i)(2) of this section or unless otherwise authorized by ATC, no person may operate an aircraft in the following airspace unless the aircraft has equipment installed that meets the requirements in paragraph (b) of this section:

  • (2) Except as provided for in paragraph (e) of this section, within 30 nautical miles of an airport listed in appendix D, section 1 to this part from the surface upward to 10,000 feet MSL;

Breaking that down: You may not operate within 30 miles of a "Mode C veil" airport unless you have a working ADS-B Out setup, or unless your aircraft was originally certificated without an engine-driven electrical setup (and has not subsequently been so certificated). The "upward to 10,000 feet" is not a loophole because once you reach that altitude paragraph (d)(4) takes effect.

But there are two general "outs" that you have available to you: the prohibitions in paragraph (i)(2) and an ATC authorization.

Paragraph (i) incorporates by reference the technical standards for ADS-B Out. I'm not sure how an operation could be prohibited by that paragraph... maybe they're saying that if your equipment is out-of-standards then you aren't allowed to use it? It isn't clear.

But the ATC authorization is easier to understand: ATC may approve a deviation from any of the ADS-B Out requirements. The FAA has set up the ADS-B Deviation Authorization Preflight Tool (ADAPT) "to manage these authorization requests." In order to be considered for a deviation, you need to have a working Mode C transponder and you need to submit the request between 24 hours and 1 hour before your flight.

The ADAPT page does have a note saying that the FAA will not issue in-flight deviations nor will ATC facilities accept requests by telephone. If this is approved FAA policy then I have not been informed of it. FAA JO 7110.65 does include a paragraph instructing controllers how to handle requests to deviate from transponder/Mode C requirements between 10,000' and 18,000' (91.215), but I do not believe there is any guidance on dealing with ADS-B deviation requests (91.225) in either JO 7110.65 or JO 7210.3. So you could make your deviation request by telephone (make sure to call a recorded line!) or over the frequency to a controller, and they may or may not approve it. Using the ADAPT would probably provide a better paper trail for everyone involved, however.



Better to be safe than sorry. If you can't comply with the Mode C veil or aren't sure (because this is a crazy big risk if unsure), you can call the approach phone number an hour before departure and you can coordinate and get permission to do the flight. They may require things like, a flight plan, being in communication with, a certain route, etc.

I forgot to mention but I'm not exactly sure of the details of your legacy transponder but if it's a 4096 with mode C and it's established to the aircraft you may be good to go. *To enter the mode C veil you need mode c. To enter the bravo you need Mode C and ADSB out.



You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .