Flight Data Recorders (FDR) and Cockpit Voice Recorders (CVR), or “black boxes” as they are better known as, are invaluable in helping air accident investigators piece together the events that led up to a crash.

Black boxes are made from a combination of electronics, insulation, and metal. They are designed to be virtually indestructible, so the crash-survivable memory units (CSMUs) can be recovered and analyzed.

Let’s take a closer look at just how black boxes are able to survive the immense force of a plane crash, and some other interesting facts.

Black Box Construction (Materials & Components)

Materials

The crash-survivable memory units (CSMUs), which are the most important part of a black box, are housed in a solid-state box that insulates and protects them through three layers of materials.

  • Aluminum housing: A thin layer of aluminum is found around the stack of memory cards.
  • High-temperature insulation: Dry-silica material is used to provide high-temperature thermal protection. The material is 1 inch thick.
  • Stainless-steel shell: The dry-silica material is contained within a 0.25 inches thick, stainless-steel cast.

What a black box is made of may not sound like much, but you will be amazed at what it can withstand and what tests the manufacturers put it through.

Components

The components that make up the construction of a black box include:

  • Power supply: The batteries are designed for 30-day continuous operation and have a six-year shelf life.
  • Crash Survivable Memory Units (CSMUs): These hold all the important flight and audio data of the plane.
  • Integrated Controller and Circuitry Board (ICB): This contains the electronic circuitry that acts as switchboard for the incoming data.
  • Underwater Locater Beacon (ULB): The ULB is invaluable in helping to identify the location of the black box in the event of an ocean crash. The beacon can transmit from depths to 14,000 ft (4,200 m).

How is a Black Box Able to Survive a Plane Crash?

A black box is able to survive a plane crash because it is designed to withstand extreme heat, jarring crashes and an immense amount of pressure.

Manufacturers thoroughly test the device by first loading sample data onto the memory boards and then performing the following tests:

  • Crash impact: Shooting the black box down an air cannon to create an impact of 3,400 Gs
  • Pin drop: Dropping a 500-pound weight with a 0.25-inch (0.64-centimeter) steel pin protruding from the bottom onto the device from a height of 10 feet (3 meters)
  • Static crush: Applying 5,000 pounds per square-inch (psi) of crush force to each of the black box’s six major axis points for five minutes
  • Fire test: Placing the black box inside a fire at 2,000 degrees Fahrenheit (1,100 Celsius) for one hour
  • Deep-sea submersion: Placing the black box into a pressurized tank of salt water for 24 hours
  • Salt-water submersion: Placing the device in a salt water tank for 30 days
  • Fluid immersion: Placing various components of the black box in aviation fluids, including jet fuel, lubricants and fire-extinguisher chemicals

What Does It Take to Destroy a Black Box?

So if a plane crash isn’t able to destroy a black box, then what can?

Well, a black box is virtually indestructible.

According to Scott Hamilton, director of Leeham Co., an aviation consulting company, “it would take a concentrated fire beyond its design strength, or an impact so high that it would be beyond what it could withstand” to destroy a black box.

Where Are Black Boxes Installed?

A black box is usually installed in the tail of an aircraft.

This is because the rear of an aircraft receives the least impact during a crash and therefore increases the device’s chances of survival.

Related: Do Helicopters Have Black Boxes?

How Much Data Can a Black Box Store?

A black box features memory boards that have enough storage space to record two hours of audio data for CVRs and 25 hours of flight data for FDRs.

Inevitably, due to the limited storage space, this data is recorded over.

What Color is a Black Box?

Despite its name, a black box isn’t actually black. It is painted bright orange to make it as easy to spot as possible in the wreckage after an accident.

The reason why a black box is called a black box is simply because when it was first developed in the early 1950s, it was painted black.