Certified Flight Instructor - Flight Instructor Airplane Practice Exam

An altitude reporting coded transponder is required for airspace:

1. From the surface to 10,000 feet MSL

2. At and above 10,000 feet MSL below Class A floor

3. Within 25 NM of a Class B primary airport

4. Above 18,000 feet MSL only

The correct answer is: At and above 10,000 feet MSL below Class A floor

An altitude reporting coded transponder is indeed required at and above 10,000 feet MSL, except when in Class A airspace. This requirement is crucial because it ensures that air traffic control has accurate altitude information about aircraft operating in this airspace, which is vital for maintaining safe separation among aircraft. The altitude reporting feature enables the transponder to transmit not only the aircraft's identification but also its altitude, allowing for better situational awareness for air traffic controllers. At this elevation, the potential for traffic encounters increases significantly, making altitude awareness even more important for safety. Aircraft operating below the Class A floor generally still need to be equipped with a transponder as indicated to provide accurate tracking. The other options pertain to different requirements. For instance, while surface to 10,000 feet MSL has its own regulations regarding visibility and communication, it does not specifically mandate the use of an altitude reporting transponder. Similarly, while within 25 NM of a Class B primary airport has its transponder requirements, they are not specifically linked to altitude reporting. Lastly, above 18,000 feet MSL alone does not encompass the broader requirement for transponder use at the crucial 10,000-foot threshold that the correct answer addresses.