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2 Answers

ADS-B required under a class Charlie shelf?

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FAA Regulations

We were having a discussion about ADS-B requirements in our local pilot forum last night. Maybe the experts here can find a definite answer to this:

Do you need to have ADS-B Out equipment to fly underneath the outer shelf of a class Charlie airspace?

Example: Let's fly across the Great Bay at 1000 MSL NE of Atlantic City.

FAR 91.225 (d) (3) can be read two ways:

  1. You need ADS-B Out when within the lateral boundaries of the Charlie, which would include anything inside the outer circle as projected to the ground, and you also need it when flying above the Charlie, or
  2. Only when both within the lateral boundaries and on top of the Charlie.

The FAA graphic suggests you don't need it under the shelf but I thought it would be worth getting an expert opinion on that.

Thank you guys!

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2 Answers



  1. AV8R on Oct 01, 2020

    ADS-B is required wherever a transponder is required.

    Class A
    Class B (Including the 30 NM veil)
    Class C (If there is no 30 NM mode C veil then you can fly under Class C without ADS-B, Also if you overfly Class C up to 10,000 ft then you need ADS-B)
    Class E above 10,000 ft.

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  2. John D Collins on Oct 02, 2020

    ADS-B is not required under the Class C shelf or a Class B shelf unless it is also inside the 30 NM mode C area. You may fly under the Atlantic City Class C shelf if you remain below 1300 MSL. You may not fly above a Class C shelf or Class B.unless you are ADS-B Out equipped. Where can you find a Class B shelf that you may fly under? Try KRHV to S74, stay below 8000 MSL. Also, you can base your aircraft at KRHV without equipping with ADS-B Out.

    The FAA choses its words carefully, most of the time. The regulation reads as:
    (3) Above the ceiling and within the lateral boundaries of a Class B or Class C airspace area designated for an airport upward to 10,000 feet MSL;

    If they wanted to mean “below”, they would not need to have carved out “above” as they could have simply worded the regulation as:
    (3) Within the lateral boundaries of a Class B or Class C airspace area designated for an airport upward to 10,000 feet MSL;

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