Where is Mode C not required?

There are two exceptions to the Mode C transponder requirement in the FAA regulation Part 91. One for gliders, balloons, and those aircraft which do not have an electrical system, and a second exemption for those who do not have a transponder installed, or who's transponder is not functioning.



Under FAA regulations in 2026, a Mode C transponder (which broadcasts the aircraft’s altitude to Air Traffic Control) is generally required in all controlled airspace, but there are specific "pockets" where it is not mandatory. You do not need Mode C when flying outside and below the "Mode C Veil" (a 30-nautical-mile radius around Class B airports) and outside of Class C airspace, provided you stay below 10,000 feet MSL. Furthermore, aircraft that were originally certified without an engine-driven electrical system (such as many vintage Piper Cubs or gliders) are exempt from the Mode C requirement while flying outside of Class B and C airspace and below 10,000 feet. There are also exceptions for flying in "Class G" (uncontrolled) airspace, which is typically found in rural or remote areas at very low altitudes. However, in 2026, even if Mode C isn't strictly required, the ADS-B Out requirement has superseded it in most busy areas, effectively making a modern transponder system a necessity for any pilot who wants to fly near major cities or above 10,000 feet.

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Mode C Transponder and Airspace In order to travel within this airspace, you absolutely must have the proper equipment, unless you are one of the exceptions – a glider, a balloon, or an aircraft without a certified engine-driven electrical system.

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Class C service requires pilots to establish two-way radio communications before entering Class C airspace. If the controller responds to a radio call with, “(a/c call sign) standby,” radio communications have been established and the pilot can enter Class C airspace.

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Without ADS-B Out, you can fly in any airspace except the ADS-B rule airspace defined by FAR 91.225 (see above). Note that ADS-B is not required in Class D airspace, or under a Class B or Class C airspace shelf, unless it lies within a Mode C veil.

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ADS-B, typically, does not outright replace your Mode C transponder but is an addition to it.

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The quick answer is NO, pilots cannot turn off the transponder while the aircraft is in flight. The transponder is a vital piece of equipment that is used to identify the aircraft to air traffic control. It also transmits important data about the aircraft, such as its altitude and speed.

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If it's failing and/or on fire, you want the power off. Two: operationally, it is sometimes necessary for ATC to request planes on the ground turn off their transponders to declutter the radar.

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Can we fly over it? Technically yes, BUT it's still a very bad idea because a motor out would force you to descend through the Class C airspace. We CAN'T fly here without special permission from ATC. Permission should be obtained in advance by telephone (some controllers will accept a radio call).

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Although the configuration of each Class C airspace area is individually tailored, the airspace usually consists of a 5 NM radius core surface area that extends from the surface up to 4,000 feet above the airport elevation, and a 10 NM radius shelf area that extends no lower than 1,200 feet up to 4,000 feet above the ...

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Class C service requires pilots to establish two-way radio communications before entering Class C airspace. If the controller responds to a radio call with, “(a/c call sign) standby,” radio communications have been established and the pilot can enter Class C airspace.

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