Which item is required for Class C airspace in addition to two-way radio communications?

• A. A 4096-code transponder and an encoding altimeter
• B. A Mode C transponder only
• C. A GPS receiver
• D. A radar beacon transponder only

Answer: (A)

Class C airspace expects you to be in two-way communication with ATC and to have an altitude-reporting transponder so your position and altitude are visible to controllers. The item that satisfies this need is a transponder that uses a 4096-code (the standard four-digit code) and an encoding altimeter. The 4096-code transponder provides your identity code, while the encoding altimeter supplies your altitude data to the transponder so ATC can see both who you are and how high you are on their radar. A GPS receiver isn’t required for Class C, and just having a radar beacon transponder without altitude encoding wouldn’t give ATC your altitude. So this combination ensures both necessary elements are present for Class C entry and operation.