Which airspace requires a mode C transponder within 30 nautical miles?

Class B airspace is the correct answer because it has specific requirements for aircraft operating within its boundaries. A mode C transponder is mandatory for any aircraft when flying within or into the vicinity of Class B airspace, typically defined as the area extending from the surface up to 10,000 feet MSL within a radius of 30 nautical miles from the primary airport. This regulation is in place to enhance safety and traffic management in busy airspace, as it allows air traffic control to identify and track aircraft more effectively.

The requirement for a mode C transponder helps ensure that ATC can maintain safe separation between a variety of aircraft operating in this high-density environment. Additionally, this transponder capability allows pilots to be aware of their altitude relative to other traffic, which is crucial in areas where frequent take-offs and landings occur.

In contrast, Class D airspace does require a transponder for certain operations, but not on the same level as Class B. Class E airspace does not universally require a mode C transponder, as its requirements depend on altitude and proximity to other airspace. Class A airspace, while it requires a transponder, is not specifically defined by a 30 nautical mile radius in relation to any primary airport. Thus