Which transponder mode is required when operating in class A airspace?

Which transponder mode is required when operating in class A airspace?

• A. Mode A
• B. Mode C
• C. Mode S
• D. No Transponder

Answer: (B)

In Class A airspace, ATC needs precise altitude information to maintain separation, so a transponder that reports altitude is required. Mode C provides altitude encoding along with the basic identification code, giving ATC your exact altitude on each reply. Mode A only transmits an identification code without altitude data, so it doesn’t meet the requirement for Class A. Mode S offers additional capabilities like selective addressing and data links, but it isn’t the baseline requirement for Class A. And flying with no transponder isn’t permitted in this airspace.

In Class A airspace, ATC needs precise altitude information to maintain separation, so a transponder that reports altitude is required. Mode C provides altitude encoding along with the basic identification code, giving ATC your exact altitude on each reply. Mode A only transmits an identification code without altitude data, so it doesn’t meet the requirement for Class A. Mode S offers additional capabilities like selective addressing and data links, but it isn’t the baseline requirement for Class A. And flying with no transponder isn’t permitted in this airspace.