Airliner Black Boxes
|Example of a Cockpit Voice Recorder (CVR)|
Despite the nickname "black box," the FDR and CVR are actually painted a bright high-visibility orange with white reflecting strips to make them easier to spot at a crash scene. The meaning of the term black box itself is somewhat unclear. Some suggest it refers to the black charring that occurs in a post-crash fire while others believe the color black is a reference to the deaths often associated with an accident investigation. The design of modern black boxes is regulated by a group called the International Civil Aviation Organization (ICAO). The ICAO determines what information the black boxes must record, over what length of time it is saved, and how survivable the boxes must be. The ICAO delegates much of this responsibility to the European Organisation for Civil Aviation Equipment (EUROCAE) that maintains a document called the Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems. Black boxes first began to appear in the 1950s and became mandatory during the 1960s. These early devices used magnetic tape for data storage, much like that used in a tape recorder. As the tape is pulled over an electromagnetic head, sound or numerical data is recorded on the medium. Analog black boxes using magnetic tape are still present aboard many planes, but these recording devices are no longer manufactured. Newer recorders instead use solid-state memory boards, called a Crash Survivable Memory Unit (CSMU), that record data in a digital format. Instead of the moving parts present in older recorders, solid-state devices use stacked arrays of memory chips similar to a USB memory stick. The lack of moving parts eases maintenance while reducing the chance of a critical component breaking in a crash. Solid-state recorders can also save considerably more data than older magnetic tape devices and are more resistant to shock, vibration, and moisture.
|Magnetic tape from within the FDR of EgyptAir 990 that crashed in 1999|
|Sample data recovered from a Flight Data Recorder|
|Diagram of data flow to aircraft black boxes|
|Interior cut-away of a black box design|
|Underwater Locator Beacon on a black box|
Other requirements specify survivability limits when immersed in liquids. The CSMU must endure the water pressure found at an ocean depth of 20,000 ft (6,100 m), and a deep-sea submersion test is conducted for 24 hours. Another saltwater submersion test lasting 30 days demonstrates both the survivability of the CSMU and the function of an Underwater Locator Beacon (ULB), or "pinger," that emits an ultrasonic signal once a second when immersed in water. These signals can be transmitted as deep 14,000 ft (4,270 m) and are detectable by sonar to help locate the recorders. A final series of tests includes submerging the CSMU in various fluids like jet fuel and fire extinguishing chemicals to verify the device can withstand the corrosive effects of such liquids. Upon completion of the testing, the black boxes are disassembled and the CSMU boards are extracted. The boards are then reassembled in a new case and attached to a readout system to verify that the pre-recorded data written to the device can still be read and processed. Another factor important to the survivability of the black boxes is their installation in the tail of the aircraft. The exact location often varies depending on the plane, but the FDR and CVR are usually placed near the galley, in the aft cargo hold, or in the tail cone. The recorders are stored in the tail since this is usually the last part of the aircraft to impact in an accident. The entire front portion of the plane acts like a crush zone that helps to decelerate the tail more slowly. This effect reduces the shock experienced by the recorders and helps to cushion the devices to improve their chances of surviving the crash.
|Flight Data Recorder recovered from United Airlines 93 in 2001|
|Animation image created using FDR data from American Airlines 587 that crashed in 2001|
|Cockpit Voice Recorder recovered from United Airlines 93 in 2001|