What is the function of a transponder in aviation, and what is its weakness?

• A. It transmits weather data
• B. It identifies an aircraft but can be turned off from the plane
• C. It provides altitude data only
• D. It never fails

Answer: (B)

The transponder’s job is to respond to radar interrogations from air traffic control, broadcasting an identification code (squawk) and, in supported modes, altitude information. This allows ATC to identify and track the aircraft on their radar displays, aiding separation and sequencing.

Its weakness is that the transponder can be turned off from the cockpit, which stops those responses and can cause ATC to lose reliable surveillance of the aircraft until the transponder is reactivated. Weather data aren’t transmitted by the transponder, and the transponder provides more than just altitude (it also conveys identity). It isn’t infallible—the possibility of being turned off or failing means it isn’t a guarantees-for-life instrument.