A flight data recorder (FDR) is a device that records information about airplane flights. Also known as a black box, it receives data via a system of sensors concerning altitude, speed, and a variety of other information. It records and saves this information about each flight the airplane takes. The FDR is built to survive a crash with its data intact and is usually located in the tail section of the plane. In case of an accident, this data is often very valuable and can help investigators figure out what happened.
Also referred to as an accident data recorder or ADR, the flight data recorder is one of two devices that records flight information. The other device is the cockpit voice recorder, which records all conversation that occurs in the airplane's cockpit between the pilot and other personnel, and is capable of saving from 30 minutes to 2 hours worth of sound. The flight data recorder receives and records information about the plane itself and can save up to 25 hours worth of data. Together these two units are often called the "black box" and can provide insight into the details of an airplane's journey.
The flight data recorder receives information about the airplane's functioning from a network of sensors located throughout the plane. The data received is recorded; depending on the age of the plane it is saved on magnetic tape or electronically. A wealth of data is compiled to give complete information about whether the airplane is operating correctly. This information includes the plane's speed, altitude, acceleration, heading or direction, fuel flow and consumption, rudder position, and control wheel position. It also records electronic signals between the airplane's systems and operation data such as the activation of various switches and controls.
The primary purpose of the flight data recorder is to provide a complete picture of flight conditions in the event of an accident when combined with the cockpit voice recorder. The unit is built to survive the extreme forces that can occur in crash situations, and is also able to survive exposure to fire and water. It is usually located in the area of the airplane that is most likely to survive a crash intact, i.e., the tail section. Once the flight data recorder is retrieved, investigators are able to use it to help recreate the events prior to a crash, and can even create computer animations of the flight. Accident investigators are able to analyze the information to figure out the cause of the crash.