Radar Contact: Dealing with Air Traffic Control Without A Transponder

There are two types of radar used in air traffic control: primary and secondary. Primary is commonly referred to as skin paint. Radio waves shoot out from a rotating radar antenna, bounce off the skin of whatever they hit, and return to the antenna. These only determine a targets location via its range and bearing from the antenna. The distance that location changes in the time between antenna sweeps is used to calculate its speed.

Key Takeaways:

• When an aircraft's transponder fails, Air Traffic Control (ATC) loses crucial secondary radar data (like altitude and squawk code) and must revert to primary radar ("skin paint") for basic target location and speed.
• To identify an aircraft without a functioning transponder, ATC employs "back to basics" methods including correlating with tower departure notifications, matching pilot-reported positions and headings to primary radar targets, or observing specific identifying turns made by the aircraft.
• Once identified, flights without a transponder require increased manual coordination from both pilots (e.g., verbally reporting altitude changes) and ATC (e.g., manual target tagging, verbal handoffs between sectors), but IFR service can generally continue with some operational restrictions.

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