Inside a Black Box and How it Works

Nov. 14, 2001 -- Information stored on the flight data recorder collected from the crash site of American Airlines Flight 587 could prove vital if investigators are able to access the data from the damaged box.

In fact, one explanation of the term "black box" dates back to World War II when air force fighters considered its more primitive predecessor — the air position indicator — as valuable as "black magic."

The description, along with the old instrument's matte black color, led to the name.

The black boxes used today by commercial airplanes are bright orange, not black, and are striped with fluorescent tape. The information they provide can hold the same "black magic" value for investigators hoping to find the cause of a crash.

Sensors Feed Two Data Units

The flight data recorder is wired to record a plane's operating data that's picked up by sensors threaded throughout the plane. The data is first sent to the flight-data acquisition unit at the front of the aircraft. This unit collects the information and beams it back to the "black box" at the tail of the plane.

The flight data recorder (and cockpit voice recorder) is located at the tail of the plane because this is usually the section of the aircraft that remains most intact following a crash.

By taking data from the flight data recorder, sometimes combining it with information taken from communication inside the cockpit, investigators generate a computer animated video reconstruction of the flight.

"The data recorder can have so much data," said Paul A. Czysz, an aviation specialist at Parks College of St. Louis University. "If they can get it, they can tell what the engines were doing, what the flight controls were doing — everything that was going on."

By regulation, the compact, steel-protected flight data recorder must monitor at least 28 different parameters. But most modern systems record more than 300 different characteristics of the flight. Flight data recorders on board Airbus aircraft, like the A-300 that crashed, are wired to pick up between 340 and 500 different kinds of data, according to Czysz.

Some of the data recorded by the devices include: time, aircraft altitude, airspeed, direction, fuel flow, horizontal stabilizer, vertical acceleration, pressure altitude, acceleration, deceleration, the angle of the wings' flaps and rudders and the control wheel position.

Built to Last, But Not Invulnerable

One lingering question in the Flight 587 investigation that flight data could answer is why the plane's rudder was set at 10 degrees to the left when it was fished from Jamaica Bay.

If flight data shows, for example, that one engine stopped working, the rudder angle could be explained since the pilot would have then set the rudder to the extreme angle to keep the plane balanced and flying straight.

Flight data recorders are built to survive. By regulation their storage units must be able to withstand an impact 3,400 times the force of gravity and fires of 2,000 degrees Fahrenheit for up to 30 minutes. They're also designed to survive submersion in 20,000 feet of saltwater for 30 days.

But as the damaged recorder from Flight 587 shows, they can't survive every crash. To overcome that problem, at least two proposals have been submitted to the Federal Aviation Administration that would enable a plane to transmit its black box information to air traffic controllers while the aircraft is in flight.

As Czysz says, "If we have this, it means it doesn't matter what happens to the recorder."