Mental Floss

What's the Deal With the Black Box?

Matt Soniak

I have spent my life on Mars, in a cave, with my fingers in my ears. What, pray tell, is a flight recorder?

Flight recorders are devices used in aircraft to record—you guessed it—flight information, which then may be used to aid any investigations into aircraft accidents or incidents.

There are two common types of flight recorders: flight data recorders (FDR) and cockpit voice recorders (CVR). FDRs record various aircraft performance parameters and operating conditions, such as time, altitude, airspeed, heading, aircraft attitude, flap position, control-column position, fuel flow and even whether the smoke alarms in the lavatory went off. The Federal Aviation Administration (FAA) requires that older commercial aircraft record a minimum of 11 to 29 parameters, depending on the size of the craft. Newer aircraft (built after 8-19-02) are required to record at least 88 parameters.

CVRs record the audio environment in an aircraft's cockpit, including conversations, ambient sounds and radio communications between the cockpit crew and others.

The FAA requires that the recording duration is a minimum of thirty minutes, and most magnetic-tape CVRs employ a continuous loop of tape that cycles every 30 minutes, recording new material over the old. Sometimes, the two recorders are combined into a single FDR/CVR unit.

Some aircraft also employ a quick access recorder (QAR), which records data on a removable storage device and can be accessed with a more-or-less regular desktop computer (FDRs and CVRs require special equipment to read the recording). QARs are usually scanned during the flight for deviations from normal operations and/or parameters so that problems can be detected and fixed before an accident even occurs.

If they're used to investigate crashes, they must be pretty tough, right?

If I had to rate the toughness of a flight recorder, I'd put it right up there with Bruce Willis in Die Hard and Clint Eastwood in Dirty Harry. Flight recorders are carefully engineered and constructed to withstand some less than comfortable conditions and usually have an impact tolerance of 3,400 Gs (one G is the g-force acting on a stationary object resting on Earth's surface. It is the force of Earth's gravity and equal to however much that object weighs. In an 3,400-G impact, the flight recorder hits something at a force equal to 3,400 times its own weight). They also have a fire resistance of 2012° F/30 minutes. They can withstand water pressure when submerged up to 20,000 feet underwater and usually have an underwater locator beacon with a six-year shelf life and 30-day operation capability.

The information the recorder gathers is stored within the device on a crash-survivable memory unit protected by aluminum housing, one inch of dry-silica material high-temperature insulation and a ¼-inch thick stainless-steel or titanium cast shell.

For high visibility in wreckage, the outside of flight recorders are coated in heat-resistant, reflective red, yellow or orange paint.

So, if it's painted red, yellow or orange, why is it called the black box?

There are a few theories about that.

The first explanation goes that after an early flight recorder for commercial flights—the "Red Egg"—was unveiled, a journalist pronounced it to be a "wonderful black box."

Another explanation says that when new electronic instruments were being added to Royal Air Force planes during World War II, they were covered in hand-made metal boxes and then painted black to prevent reflection. These electronics came to be collectively known as "black boxes" and the term then made its way into civil aviation and general usage post-war.

Still another explanation has it that the name is simply borrowed. In science and engineering, a "black box" is a device, system or object that can viewed solely in terms of input, output and transfer characteristics without any knowledge of its internal workings.

How do you read a black box and what do you do with the info?

At the NTSB labs, the black box data is downloaded onto computers equipped with readout systems and analysis software supplied by the black box manufacturers. Extracting the data from a relatively undamaged recorder only takes a few minutes. In the case of a badly dented or burned recorder, the box has to be disassembled and the memory units removed, cleaned and connected to a working recorder.

The data on a CVR is reviewed and interpreted by a team of experts, usually including a representative from the airline involved in the accident, a representative from the airplane manufacturer, an NTSB transportation safety specialist and an NTSB air safety investigator. Meanwhile, the data on an FDR is used by NTSB investigators to reconstruct the events and conditions of the flight (FDRs are also used to analyze aircraft engine performance, the condition of aircraft parts and instruments and air safety issues). These processes can take weeks or even months, but, ideally, provide the investigators with some insight into the final moments of the flight and what caused the accident.