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Friday, June 11, 2010

Do you know ?

Whenever a plane crash happens we hear a lot about black box and read a lot about black box . But what is exactly a black box and what are its functions. If you are interested read this.

Airliner Black boxes

The "black box" is a generic term for two recording devices carried aboard commercial airliners. The Flight Data Recorder (FDR) records a variety of parameters related to the operation and flight characteristics of the plane. The Cockpit Voice Recorder (CVR) records the voices of the flight crew, engine noise, and any other sounds in the cockpit. All large commercial airliners and certain varieties of smaller commercial, corporate, and private aircraft are required by law to carry one or both of these boxes, which generally cost between $10,000 and $15,000 apiece. The data these devices provide is often invaluable to experts investigating the events leading up to an accident. The recovery of the boxes is one of the highest priorities in any mishap investigation, second only to locating survivors or recovering the remains of victims. FDR information is also often used to study other aviation safety issues, engine performance, and to identify potential maintenance issues. 

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.

Whatever the medium used to record the data, the purpose of the black boxes is to collect information from various sensors aboard an aircraft. The Cockpit Voice Recorder, for example, saves sounds from microphones located on the flight deck. An area microphone is typically placed in the overhead instrument panel between the pilots, and an additional microphone is located in the headset of each member of the flight crew. These microphones pick up conversations between the flight crew, engine noises, audible warning alarms, landing gear sounds, clicks from moving switches, and any other noises like pops or thuds that might occur in the cockpit. The CVR also records communications with Air Traffic Control, automated radio weather briefings, and conversations between the pilots and ground or cabin crew. These sounds often allow investigators to determine the time of key events and system failures.

Power for the black boxes is provided by electrical generators connected to the engines. The generators on most large airliners produce a standard output of 115 volt, 400 hertz AC power while some smaller planes instead generate 28 volt DC power. Black boxes are typically designed to use only AC or DC power but not either one. Recorders built for compatibility with the AC power supplies on larger planes cannot be used on small DC-powered aircraft. In the event of engine failure, larger aircraft are also equipped with emergency backup power sources like the auxiliary power generator and ram air turbine to continue operating the black boxes. In addition, the ICAO is considering making a battery mandatory on solid-state recorders to provide an independent power supply in the event of a complete power failure aboard the plane.

Current regulations require the black boxes to survive an impact of 3,400 g's for up to 6.5 milliseconds. This rapid deceleration is equivalent to slowing from a speed of 310 miles per hour (500 km/h) to a complete stop in a distance of just 18 inches (45 cm). This requirement is tested 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 black boxes must also survive a penetration test during which a steel pin dropped from a height of 10 ft (3 m) 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 5,000 pounds per square inch (350 kg/cm�) for five minutes. The fire resistance of the CSMU is further tested by exposing it to a temperature of 2,000�F (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 500�F (260�C). 


Flight Data Recorder information is typically presented in the form of graphs or animations used to understand instrument readings, flight characteristics, and the performance of the aircraft during its final moments. Cockpit Voice Recorder information is usually more sensitive and laws strictly regulate how it is handled. A committee including representatives of the NTSB, FAA, the airline, the manufacturers of the aircraft and engines, and the pilots union is responsible for preparing a transcript of the CVR's contents. This transcript is painstakingly created using air traffic control logs and sound spectrum analysis software to provide exact timing. Although the transcript can be released to the public, only select and pertinent portions of the actual audio recording are made public due to privacy concerns.


1 comment:

Saras said...

Very useful and informative post.