Where is a mode C transponder required?

A mode C transponder is required in multiple airspace classifications and at certain altitudes to ensure effective radar tracking of aircraft and to enhance overall safety in the national airspace system. Specifically, mode C transponders are necessary in Class B airspace, which encapsulates busy terminals, and in Class C airspace that typically surrounds airports with a significant amount of air traffic.

Additionally, a mode C transponder is mandated for all aircraft flying at altitudes above 10,000 feet MSL, except in airspace that is below 2,500 feet AGL. The requirement for a transponder in these specific classifications and altitudes helps air traffic control maintain situational awareness and effectively manage traffic, thus reducing the risk of mid-air collisions.

By understanding the regulations regarding the use of transponders in various classes of airspace and their altitude restrictions, pilots can ensure compliance and enhance the safety of their operations within the National Airspace System.