What is the function of Transponder Mode C in ATC surveillance?

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Multiple Choice

What is the function of Transponder Mode C in ATC surveillance?

Mode C is about automatic altitude reporting to ATC through the secondary surveillance radar. When ATC interrogates a transponder, the reply includes the Mode A code (squawk) and an altitude value encoded by Mode C. That altitude represents the aircraft’s pressure altitude in feet (typically in 100-foot increments), which gives controllers reliable vertical separation information. Primary radar shows returns without cooperative data, so it doesn’t provide altitude, heading, or airspeed. The function described is specifically about altitude data, not color displays or other parameters.

Mode C is about automatic altitude reporting to ATC through the secondary surveillance radar. When ATC interrogates a transponder, the reply includes the Mode A code (squawk) and an altitude value encoded by Mode C. That altitude represents the aircraft’s pressure altitude in feet (typically in 100-foot increments), which gives controllers reliable vertical separation information. Primary radar shows returns without cooperative data, so it doesn’t provide altitude, heading, or airspeed. The function described is specifically about altitude data, not color displays or other parameters.

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