An operable 4096-code transponder and mode C encoding altimeter are required in which airspace?

• A. Class B airspace and within 30 miles of the Class C airspace
• B. Class A airspace
• C. Class D airspace
• D. All airspace

Answer: (A)

This question focuses on where a transponder with altitude reporting is required to operate. In the United States, Class B airspace requires an operable transponder with altitude encoding (Mode C). Additionally, the rule extends to the area within 30 miles of the primary Class C airport to ensure ATC can identify and manage traffic in radar coverage around busy Class C airspace. So the specific airspace where both a 4096-code transponder and Mode C are required is Class B airspace and the region within 30 miles of the Class C airspace. The other options don’t match this exact combination of airspace and distance.