FAA Ground School Practice Test

What must aircraft within 30 miles of a Class B primary airport from the surface upward to 10,000 feet MSL be equipped with?

1. Operable Altimeter

2. Mode A transponder only

3. Operable transponder with mode S or 4096-code capability

4. Mode D transponder

The correct answer is: Operable transponder with mode S or 4096-code capability

Aircraft operating within 30 miles of a Class B primary airport, extending from the surface up to 10,000 feet MSL, are required to be equipped with an operable transponder that has Mode S or 4096-code capability. This regulation is crucial for maintaining safety and efficient air traffic control in busy airspace associated with Class B airports. The reason for this requirement rests on the need for precise identification and tracking of aircraft in areas that typically experience high traffic volumes. Mode S transponders not only transmit a unique identifier but also allow for communication between the aircraft and ground stations. This two-way communication enhances situational awareness and contributes to collision avoidance measures, which is particularly important near Class B airports where many aircraft are operating in close proximity to each other. In contrast, while an operable altimeter is essential for overall flight safety, it does not specifically provide the tracking capabilities required in such airspace. Mode A transponders, while functional, lack advanced features found in Mode S transponders and do not provide the same level of situational awareness. A Mode D transponder is not a recognized classification used in current regulations; typically, transponder capabilities are referred to as Mode A, C, or S.