In which airspace are aircraft required to have an operating transponder with Mode C?

In which airspace are aircraft required to have an operating transponder with Mode C?

• A. Class A
• B. Class B
• C. Class C
• D. Class D

Answer: (A)

Altitude information from a transponder is how ATC keeps track of both position and level of aircraft, which is essential for safe separation. In Class A airspace, this requirement is absolute for any operation: you must have an operating transponder with altitude reporting (Mode C) and you must be in two-way radio communication with ATC on an approved frequency. Because Class A is the airspace where ATC has the most direct control and IFR traffic predominates, having Mode C in this space is non-negotiable for entry and operation. While transponder with Mode C is also used in other airspaces—most notably in Class B and Class C, and within the Mode C veil around Class B airports—the question points to the space where the requirement is unconditionally applicable for all operations, which is Class A.

Altitude information from a transponder is how ATC keeps track of both position and level of aircraft, which is essential for safe separation. In Class A airspace, this requirement is absolute for any operation: you must have an operating transponder with altitude reporting (Mode C) and you must be in two-way radio communication with ATC on an approved frequency. Because Class A is the airspace where ATC has the most direct control and IFR traffic predominates, having Mode C in this space is non-negotiable for entry and operation.

While transponder with Mode C is also used in other airspaces—most notably in Class B and Class C, and within the Mode C veil around Class B airports—the question points to the space where the requirement is unconditionally applicable for all operations, which is Class A.