We all saw the image of the Air India official carrying the charred black box of the crashed flight in Mangalore flashing on our television screens. Few of us,however,know much about the box and how it works. To begin with,contrary to what the name suggests,the black box isnt black in colour.
As per guidelines given by Joint Airworthiness Requirements (JAR),the box is painted either bright red or orange,with white reflecting stripes,to make it easier to locate. Why is it called a black box? Perhaps because of its association with airplane tragedies.
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. While analog black boxes using magnetic tape can still be found aboard many planes,on April 1,2000 JAR made it mandatory for all aircraft weighing more than 5,700 kg and those with a seating capacity of more than nine to be equipped with a Digital Flight Data Recorder (DFDR). Today,the DFDR,along with the Cockpit Voice Recorder (CVR),is known as the black box.
The layman looks at it as a device that records the voices of the pilots,because of which there is a misconception that the black box is situated in the cockpit. The black box is located at the rear of the aircraft,normally under the fin. The reason behind this is that in case of an accident,the rear end of the flight is least likely to be damaged, says captain Arvind Bhat,a category A instructor,air force examiner and VVIP pilot who has flown the likes of Indira Gandhi,Rajiv Gandhi,V.P. Singh,Giani Zail Singh and others.
A black box,costing $10,000-15,000 and housed in a shock and water resistant box that can sustain force eight times the gravitational acceleration (9.8m/sec square),generates a record of the flight. Five minutes before the take off,the cabin crew and the engineers inspect the flight. The DFDR and CVR are switched on by the captain and the co-pilot when they start the engine. Not that the recording is dependent on them because if they forget,both these devices are turned on automatically the moment the wheels lift off the ground, says Bhat.
JAR makes it mandatory for the DFDR to record 32 specifications,however,the current DFDRs record about 65 different parameters that include the minutest of engine details,along with altitude,airspeed,heading,acceleration,thrust power,configuration of lift and drag devices,use of automatic flight control devices,angle of attack and so on. From the earlier capacity of 10 hours,the DFDRs today have a recording memory of 25 hours. In other words,they are a summary of the entire flight. Minute parameters such as the pitching or rolling of the plane,navigational information,cockpit warnings,gear positions,different tiltings of the plane during the journey,are all recorded by the DFDR, says Bhat.
The CVR,on the other hand,records the minutest sounds in the cockpit with the help of five area mikes located randomly within the cockpit. From conversations that the pilots have with the stations to tuning the frequency of ground radio stations and from the sipping of coffee to replying to a co-pilot,the CVR records everything. The recording capacity of a CVR is two hours,so after recording two hours of conversations,the CVR will erase the earlier data and start recording new data on it. The CVR thus makes available the data only two hours prior to a crash, says Bhat.
In the Air France Airbus A 330 crash in the Atlantic Ocean that took place in June last year,killing 228 passengers,the black box played a major role in locating the plane in the sea,and the ground staff at the Charles De Gaulle airport,Paris,knew much before the pilots that the plane was heading for trouble. Bhat says what made this possible is the Airborne Communications Addressing and Reporting System (ACARS),wherein the black box is linked to the ground operations of the airline. With the help of data link communication,these black boxes continuously keep transmitting information to the ground operations. Not only that,the black boxes these days are such that they transmit radio waves the moment they touch water. It was a similar black box on Airbus A 330 that kept transmitting signals from a depth of about five miles in the middle of the ocean.
A bible in case of an unfortunate mishap,Bhat says that there have been no known cases wherein the black box has got damaged. Obtaining information from the black box needs skilled professionals. There are times when these boxes are sent to the UK or the US for that reason, says Bhat.