Mode A transponder capabilities include which of the following?

• A. Identifies aircraft; Position
• B. Pressure altitude only
• C. Altitude and heading
• D. Radar contact time

Answer: (A)

Mode A is about identifying aircraft. When the transponder is queried by air traffic radar, it responds with a four-digit squawk code that uniquely identifies the aircraft to the controller. That identification makes it possible for the radar to track and reference the airplane on the controller’s display, effectively linking the aircraft’s identity to its position on the radar screen. Mode A itself does not provide altitude, heading, or timing information—that kind of data comes from other systems or modes. Pressure altitude, for example, is provided by Mode C; altitude and heading aren’t transmitted by Mode A; and radar contact time isn’t a transponder capability. So the primary, best-supported capability of Mode A is identifying the aircraft, which in turn supports locating it on radar.