Testing Tuesday: Class C Airspace Requirements

The correct answer is a: Two way communications and Mode C transponder.

AIM 3-2-4 states that operating equipment required to fly in class C airspace includes two way communication and a transponder with automatic altitude reporting equipment (Mode C).

A Mode C transponder is not only required IN class C airspace, but also ABOVE class C airspace up to 10,000 feet MSL (see AIM 4-1-20). You can, however, fly below a class C shelf without having a Mode C transponder, or for that matter, any transponder at all. Class C shelf airspace generally begins no lower than 1200 feet above the airport elevation (generally AGL), and extends to 4000 feet AGL (in most cases).

It’s worth noting that Air Traffic Control can authorize flight into class C airspace without an altitude encoding transponder. According to 14 CFR Part 91.215(d), you can make a request at any time if you are flying an aircraft that has a transponder that is not Mode C or does not have altitude encoding equipment (or has had a failure of the altitude encoding functionality), and ATC can approve that deviation from the Mode C requirement. If an aircraft has a failed transponder and is flying to a destination where the transponder can be fixed (including any stops along the way), ATC can also approve a deviation at any time. If you happen to be flying a plane that does not have and electrical system or does not have a transponder installed, ATC can approve a deviation, but the request must be made at least 1-hour before the operation is to be conducted.

For more information on transponder operation, see AOPA’s Transponder Requirements page.

Now, for the two-way communications part: the gist of this part is, if ATC responds to your call using your tail number, two way communications have been established, and you can enter class C airspace, even without a specific clearance to do so. howeer, if ATC does not respond, or responds without using your tail number (by saying something such as “Aircraft calling Columbus Approach, standby”), then two-way communications have NOT been established, and you may not enter class C airspace. Obviously, if ATC says “remain clear of class C airspace,” regardless of whether they use your tail number or not, you must not enter their airspace.