How Does a Black Box Survive a Plane Crash?

In the aftermath of a plane crash, investigators typically comb through debris for answers. Much like a jigsaw puzzle, they use their findings to piece together a clearer picture of what went wrong and, importantly, how to prevent it from happening again. Among the most useful tools during these investigations is a flight recorder, also known as a black box.

Even when the rest of the aircraft is reduced to rubble, black boxes are expertly designed to withstand immense physical force and other destructive factors. You may be wondering, if a flight recorder can survive a crash, why not make the entire plane out of that material? Unfortunately, it’s not as simple as that. 

It’s not just the material it’s made of, but also multiple other security layers that ensure a flight recorder’s durability.

Built To Last

The name “black box” is actually a misnomer, as these devices are painted bright orange — like a traffic cone or safety vest – to make them easier to spot and recover from crash sites. There are actually two black boxes located in all large passenger aircraft (and certain smaller airplanes), a requirement of the Federal Aviation Administration. 

One black box is the flight data recorder, which stores thousands of different important metrics, including the plane’s altitude, airspeed, and heading. The other is the cockpit voice recorder, which stores audible radio transmissions, general engine noises, and the sound of the pilots talking to one another, whether it’s about what they ate for lunch or problems with the controls.

Both of these recording devices are designed to withstand the same extreme thresholds. Black boxes can endure up to 3,400 Gs of physical impact, which is equal to being thrust into a concrete wall at 310 miles per hour. At most, Formula 1 drivers only sustain about 6.5 Gs, or 6.5 times the force of Earth’s gravity. 

Black boxes are also built to survive temperatures of up to 2,000 degrees Fahrenheit, roughly equal to the temperature of flowing molten lava. Since planes often fly over the ocean, flight recorders are also designed to endure depths of up to 20,000 feet beneath the waves — roughly 7,500 feet deeper than the location of the Titanic. 

To make underwater recovery easier, black boxes are outfitted with a built-in pinging device, which is activated when immersed in water. The box can transmit a clear homing signal from depths up to 14,000 feet. The underwater locator beacon (#6 in the illustration below) is kept on the outside of the box so it can transmit a clear signal.

The ability to endure extreme force, heat, and pressure is made possible by the way that black boxes are constructed. A black box keeps its recording electronics (#5 in the illustration above) and power supply (#4) on one end — it’s not protected by much because it doesn’t need to be. The information the instruments gather is immediately saved to memory boards (#1), and thus the electronics are expendable after a crash. 

It’s the data that’s needed, which is why the memory boards lie at the very core of the flight recorder. The central data storage unit is wrapped in a thin layer of aluminum and a 1-inch-thick layer of dry silica (#2), which works to absorb heat and protect the central component from melting. 

This layer is itself encased within a quarter-inch of stainless steel or titanium (#3), providing much-needed protection against potential corrosion or any traumatic impacts. While it would be nice if airplanes were built entirely out of these durable metals, stainless steel is too heavy and titanium too expensive for that to be practical.

Once a black box is built, it’s put through the ringer to make sure it’s up to snuff. Tests include being launched out of an air cannon into an aluminum target, being crushed by 5,000 pounds per square inch of force for five minutes, and being subjected to 2,000-degree flames for an hour straight. It even has a 500-pound weight (with a protruding pin) dropped onto it like some unfortunate cartoon character.

Testing a flight recorder is no laughing matter, though. The information retrieved from one after a crash can potentially save many lives in the future.