Within 30 miles of a Class B primary airport from the surface up to 10,000 feet MSL, aircraft must be equipped with what transponder capability?

Within 30 miles of a Class B primary airport from the surface up to 10,000 feet MSL, aircraft must be equipped with what transponder capability?

• A. An operable transponder with Mode S or 4096 code capability with Mode C altitude reporting
• B. A basic transponder
• C. No transponder
• D. A transponder with Mode A only

Answer: (A)

The main idea is that ATC needs precise altitude information when you’re in the busy Class B airspace. Within 30 miles of a Class B primary airport from the surface up to 10,000 feet MSL, you must have an operable radar beacon transponder that provides automatic altitude reporting. That means the transponder has to provide altitude data to ATC, not just identification. A transponder with Mode C altitude reporting satisfies this requirement, and a Mode S transponder also works because it includes altitude information. If your transponder is only a basic Mode A unit (no altitude reporting), it does not meet the rule. Similarly, a transponder that provides a 4096 code with Mode C altitude reporting is acceptable because it delivers the necessary altitude data. So the correct choice is the one that specifies an operable transponder with altitude reporting capability, either Mode S or 4096 code capability with Mode C.

The main idea is that ATC needs precise altitude information when you’re in the busy Class B airspace. Within 30 miles of a Class B primary airport from the surface up to 10,000 feet MSL, you must have an operable radar beacon transponder that provides automatic altitude reporting. That means the transponder has to provide altitude data to ATC, not just identification.

A transponder with Mode C altitude reporting satisfies this requirement, and a Mode S transponder also works because it includes altitude information. If your transponder is only a basic Mode A unit (no altitude reporting), it does not meet the rule. Similarly, a transponder that provides a 4096 code with Mode C altitude reporting is acceptable because it delivers the necessary altitude data. So the correct choice is the one that specifies an operable transponder with altitude reporting capability, either Mode S or 4096 code capability with Mode C.