A brief history of Black Box (still being searched in lattest tragic incident)


A flight data recorder (FDR) (also ADR, for accident data recorder) is a kind of flight recorder. It is a device used to record specific aircraft performance parameters. Another kind of flight recorder is the cockpit voice recorder (CVR), which records conversation in the cockpit, radio communications between the cockpit crew and others (including conversation with air traffic control personnel), as well as ambient sounds. In some cases, both functions have been combined into a single unit. The current applicable FAA TSO is C124b titled Flight Data Recorder Systems.[1]

Popularly referred to as a "black box", the data recorded by the FDR is used for accident investigation, as well as for analyzing air safety issues, material degradation and engine performance. Due to their importance in investigating accidents, these ICAO-regulated devices are carefully engineered and stoutly constructed to withstand the force of a high speed impact and the heat of an intense fire. Contrary to the "black box" reference, the exterior of the FDR is coated with heat-resistant bright Red paint for high visibility in wreckage, and the unit is usually mounted in the aircraft's empennage (tail section), where it is more likely to survive a severe crash. Following an accident, recovery of the "black boxes" is second in importance only to the rescue of survivors and recovery of human remains

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THERE is a common misconception that black boxes are indestructible. No manmade device is indestructible, and no material has ever been developed that cannot be destroyed under severe enough conditions.

The black boxes are instead designed to be highly survivable in a crash. In many of the worst aviation accidents, the only devices to survive in working order are the Crash Survivable Memory Units (CSMUs) in the black boxes. The remainder of the recorders, including the external case and other internal components, are often heavily damaged.

The CSMU, however, is contained within a very compact cylindrical or rectangular box designed to safeguard the data within against extreme conditions.

The box is composed of three layers to provide different types of protection to the recording medium. The outermost shell is a case made of hardened steel or titanium designed to survive intense impact and pressure damage.
The second layer is an insulation box while the third is a thermal block to protect against severe fire and heat. Together, these three layered cases allow the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) to survive in all but the most extreme crash conditions.

Current regulations require black boxes to survive an impact of 3,400 g ’ s for up to 6.5 milliseconds (where g is the gravitational constant). This rapid deceleration is equivalent to slowing from a speed of 500 kilometres per hour to a complete stop in a distance of just 45 centimetres. This requirement is tes ted by firing the CSMU from an air cannon to demonstrate the device can withstand an impact force at least 3,400 times its own weight. The box must also survive a penetration test during which a steel pin dropped from a height of three metres impacts the CSMU at its most vulnerable point with a force of 500 pounds (2,225 N).

In addition, a static crush test is conducted to demonstrate that all sides of the CSMU can withstand a pressure of 350 kilograms per square centimetre for five minutes. The fire resistance of the CSMU is further tested by exposing it to a temperature of 1,100°C for up to an hour.

The device is also required to survive after lying in smoldering wreckage for ten hours at a temperature of 260°C. UNDERWATER LOCATOR BEACON: Other requirements specify survivability limits when immersed in liquids. The CSMU must endure the water pressure found at an ocean depth of 6,100 metres, 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 4,270 metres 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, 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.

[Dawn, July 31st 2010]

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Faseeh