What are the two main types of transponders used in aviation?

In aviation, transponders are crucial for identifying and communicating with air traffic control. Mode S and Mode C are two significant types of transponder systems. Mode C transponders provide altitude information in addition to the aircraft's identification code, enhancing situational awareness for air traffic controllers. Mode S transponders, an advanced version, not only transmit identification and altitude but also allow for selective addressing capabilities, enabling communication with specific aircraft and improving data exchange in busy airspace.

These two modes are integral for maintaining safety and efficient separation of aircraft. The distinction between Mode S and Mode C helps ensure that various operational requirements can be met, especially in environments with high traffic density. Their functionalities support the effective implementation of Air Traffic Management (ATM) systems that rely on accurate and timely data for flight operations.

Other options refer to different categorizations or characteristics of transponders that might not reflect the primary operational standards widely recognized in aviation.