by October 12, 2002 0 comments

In the event of a plane crash, the first thing investigators turn to is the black box. This little device records all information useful in determining the cause of the crash. But what is the black box? How does it survive even the worst accidents? How and what kind of information does it store?

The black box is placed in all aircraft, be it commercial or fighter. It consists of two components: the Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR). In an FDR, flight data parameters are recorded through sensors that connect various areas of the plane to the Flight Data Acquisition Unit, which in turn is connected to the FDR. The most common parameters recorded are time, pressure, altitude, airspeed, vertical acceleration, magnetic heading, control column position, rudder pedal position, control wheel position, horizontal stabilizer and fuel flow. There are a total of 88 parameters that have to be recorded by any FDR. The FDR can store up to 25 hours of flight data.

The Blacj Box

The CVR records all voices and sounds in the cockpit through microphones connected to an Associated Control Unit

One microphone is in the pilot’s headset and another in the cockpit’s center. The ACU provides pre-amplification to the voice and passes it to the CVR, which can store at least 2 hours of sound. Black boxes are fitted in a plane’s rear because it takes the least impact of the crash.

Data from both FDR and CVR gets stored on stacked memory boards located in what’s called the Crash Survivable Memory Unit (CSMU). These contain flash memory chips having capacity between 4 to 192 MB. The unit usually has a microprocessor such as an Intel 486 and can use various types of interfaces for connecting to external monitoring and analysis devices. These include standard RS-422, 10-Base-T Ethernet, IEEE 1394A/B or USB interfaces. There’s also a 0.5 to 2 MB EEPROM containing an embedded OS and application for controlling it. There’s a PCMCIA-based receptacle for the FDR. After a crash, usually some sort of a handheld unit is used to download the data onto a PCMCIA memory cartridge over a RS-422 serial link. Finally, there’s standard Windows-based software that’s used for analyzing the data.

What makes the black box invincible
The secret is in the CSMU we just talked of, which is in the shape of a large cylinder fixed onto the recorder. The CSMU can survive extreme heat, fire, violent crashes and pressure conditions. It is made of three layers, with the innermost layer

Who invented the black box?

Although it was the Wright Brothers who pioneered the use of a device to record propeller rotations, it was David Warren who invented the black box. Born in 1925 in the Gulf of Carpentaria in North Australia, he became interested in electronics in school and began building radios. Although he led his lifetime profession in chemistry, his interest in electronics did not decline. During his investigation of the crash of The Comet (the first jet-powered aircraft) in 1953, he argued that a recording made during a flight can help solve air-crash mysteries and thus invented the first Flight Data Recorder (Black Box).

containing the memory cards covered by thin aluminum. Over this, it has a layer made of dry silica 1-inch thick, used for high temperature insulation. The outermost layer consists of a stainless steel shell that is 0.25 inch thick. Some black boxes have a titanium shell.

The CSMU goes through rigorous test stages. It is shot from a cannon gun to create an impact of 3400G (1G is earth’s gravitation force). It is also crushed for 5 minutes at 5000 pounds per square inch from all 6 axes, and is burnt with a propane source fireball at 1,100º C for one hour. During this test, everything in the black box, including the memory interface cable, motherboard and other circuitry get burnt away. Only the CSMU survives.

PCQ Labs

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