With any airplane crash, there are many unanswered questions as to what brought the plane down. Investigators turn to the airplane’s flight data recorder (FDR) and cockpit voice recorder (CVR), also known as “black boxes,” for answers. In Flight 261, the FDR contained 48 parameters of flight data, and the CVR recorded a little more than 30 minutes of conversation and other audible cockpit noises.
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.
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 orange 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.
Although many of the black boxes in use today use magnetic tape, which was first introduced in the 1960s, airlines are moving to solid-state memory boards, which came along in the 1990s. Magnetic tape works like any tape recorder. The Mylar tape is pulled across an electromagnetic head, which leaves a bit of data on the tape.
Solid-state recorders are considered much more reliable than their magnetic-tape counterparts. Data from both the CVR and FDR is stored on stacked memory boards inside the crash-survivable memory unit (CSMU). In recorders made by L-3 Communications, the CSMU is a cylindrical compartment on the recorder. The stacked memory boards are about 1.75 inches (4.45 cm) in diameter and 1 inch (2.54 cm) tall.
The memory boards have enough digital storage space to accommodate two hours of audio data for CVRs and 25 hours of flight data for FDRs.
Airplanes are equipped with sensors that gather data. There are sensors that detect acceleration, airspeed, altitude, flap settings, outside temperature, cabin temperature and pressure, engine performance and more. Magnetic-tape recorders can track about 100 parameters, while solid-state recorders can track more than 700 in larger aircraft.
All of the data collected by the airplane’s sensors is sent to the flight-data acquisition unit (FDAU) at the front of the aircraft. This device often is found in the electronic equipment bay under the cockpit. The flight-data acquisition unit is the middle manager of the entire data-recording process. It takes the information from the sensors and sends it on to the black boxes.
Any sounds in the cockpit are picked up by these microphones and sent to the CVR, where the recordings are digitized and stored. There is also another device in the cockpit, called the associated control unit, that provides pre-amplification for audio going to the CVR. Here are the positions of the four microphones:
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Pilot’s headset
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Co-pilot’s headset
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Headset of a third crew member (if there is a third crew member)
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Near the center of the cockpit, where it can pick up audio alerts and other sounds
Most magnetic-tape CVRs store the last 30 minutes of sound. They use a continuous loop of tape that completes a cycle every 30 minutes. As new material is recorded, the oldest material is replaced. CVRs that used solid-state storage can record two hours of audio. Similar to the magnetic-tape recorders, solid-state recorders also record over old material.
Ethiopian Airlines Plane crash ‘similar’ to Earlier Disaster
Say, British investigators
British aviation lawyers have launched their own investigation into last week’s Ethiopian airliner crash and are examining similarities with another air disaster less than three years ago.
Ethiopian Airlines’ flight 409 caught fire five minutes after take-off from Beirut on Monday and plummeted into the Mediterranean two miles off the Lebanese coast, killing all 89 passengers and crew, including two Britons.
The plane crashed in similar circumstances to a Kenya Airways plane that came down in Cameroon in May 2007 killing all 114 people on board.
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