Black boxes : surprising facts
Here are some things you might not know about black boxes:
Orange Is the New Black
First, the black box is neither black, nor a box! The black box is actually a cylinder mounted on two large pieces of metal and looks more like an air compressor than a tape recorder. The term “box” refers to when the recordings were made on metallic tapes, which have been replaced by digital memory boards. While some older models do still exist, most are slated for replacement.
Also, black boxes are not black. The term “black box” is favoured by the media, but most people in the know don’t call them that. There are several theories for the original of the name “black box”, ranging from early designs being perfectly dark inside, to a journalist’s description of a “wonderful black box”, to charring that happens in post-accident fires.
So, black boxes are orange! Since that, as you can imagine, is easier to find in a forest of rubble.
A ‘black box’ comes in two parts
The “black box” is made up of two separate pieces of equipment: the flight data recorder (FDR) and a cockpit voice recorder (CVR). They are compulsory on any commercial flight or corporate jet, and are usually kept in the tail of an aircraft, where they are more likely to survive a crash.
FDR records at least 88 required parameters about the flight, including airspeed, altitude, rudder position, wheel position, air pressure, and (if you believe the flight attendants) who still has their cell phone on at takeoff. CVR records everything the folks in the front cabin are talking about! While the old magnetic-tape versions could store up to 30 minutes of talk at a time, the current digital recorders can record up to two hours (which, honestly, still seems low). Once that two hours is reached, the CVR records over old material.
One more interesting fact: recorders were originally housed in the cockpit along with the instruments and the pilots. Only after several accidents where the Flight Data Recorder was not recoverable did they get moved to the rear of the aircraft, based on the presumption that following the initial impact, the rear of the aircraft would be moving at a slower speed. In addition, the units initially only had to withstand a 100gs impact which was increased to 1000gs.
From Down Under
Flight data recorders, or “black boxes,” have their history in the earliest days of aviation as the Wright Brothers carried data recorders on one of their initial flights. They created a device which recorded propeller rotations, distance travelled and time spent in the air. This initial recorder was very crude and only recorded limited flight data including duration, speed and number of engine revolutions.
Australia was the first country to make cockpit voice recorders a requirement for commercial aircraft.
- Black boxes go through a whole sequence of surviveability testing including:
Crash Impact Test — It has been agreed that 3400gs for 6.5 ms would be required to meet most accident scenarios. This test is actually performed with a cannon. A Fairchild CVR has survived a crash that was estimated to be more than 6000 gs.
Static Crush — In this test, 5,000-pound pressure is applied against all six axis points.
Pierce Test — A pierce test employs a 500-lb. weight dropped from 10 feet. It has been modified to be performed with a hardened steel pin.
Fire Test — The devices are subjected to 1100 degrees Centigrade for 60 minutes, then undergo 10 hours at 260 degrees Centigrade.
Then, testers drop black boxe into a pressurized saltwater tank, simulating the water pressure at 20,000ft below the surface. For 24 hours. In a slightly less-pressurized environment, it must then survive 30 days completely submerged in saltwater.
If all that goes well, then the unit is run through a series of diagnostic tests to see if it still works.
It can take a long time to find one.
Black boxes are fitted with an underwater locator beacon that starts emitting a pulse if its sensor touches water. It means that black boxes can only be detected if the aircraft is under water. If a crash happens on land, searchers only have the orange color as a visual beacon.
When black boxe touches water, they work to a depth of just over four kilometres, and can “ping” once a second for 30 days before the battery runs out, meaning MH370‘s black box stopped pinging around April 7, 2014. After Air France flight 447 crashed into the Atlantic Ocean, it took search teams two years to find and raise the black boxes. They provided valuable information about what actually happened prior to the crash.
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