A transponder is a common device that’s found on most airplanes. In the United States, most airplanes are required to have one. The only exception is non-electrical aircraft that fly at an altitude below 10,000 feet, such as balloons and gliders. What is a transponder exactly, and why do airplanes use them?
The Basics of Transponders and How They Work
A transponder is a device that emits an air-based signal upon the reception of a signal from the ground. Also known as an XPDR, TPDR and TP, it’s used to help air traffic controllers locate airplanes. Air traffic controllers can send a radio-frequency signal to an airplane, at which point the airplane’s transponder will respond with its location. Air traffic controllers can then use this information to determine where the airplane is located almost instantly.
At any given time, there are around 10,000 to 20,000 airplanes in the air. To prevent midair collisions, as well as other accidents, air traffic controllers must keep an eye on where these airplanes are located. If two airplanes are approaching each other, air traffic controllers can contact their respective pilots to direct a change of course.
Air traffic controllers work from ground-based stations, such as towers. At these stations are radars that communicate with airplanes and their transponders. Air traffic controllers can send a signal to an airplane, and the airplane’s transponder will respond with its location and squawk code (see below).
The ‘Squawk’ Code
Transponders work in conjunction with a squawk code. A squawk code is a unique identifier that associates a transponder with an airplane. Prior to taking off, pilots must enter the squawk code so that air traffic controllers can identify them.
Each flight has a squawk code. When replying to air traffic controllers, the transponder will send the airplane’s location and its squawk code. Squawk codes are important because they allow air traffic controllers to identify specific flights. If an airplane doesn’t have a squawk code, they won’t know which flight it is. Air traffic controllers may receive its location, but the squawk code is ultimately what identifies airplanes in the air.
A transponder is a small device that receives and sends radio signals. It’s used to tell air traffic controllers the flight and location of an airplane. With this information, air traffic controllers can better manage the tens of thousands of airplanes in the air to prevent accidents from occurring.