Airplane crashes are violent affairs. In many such accidents, the only devices that survive are the crash-survivable memory units (CSMUs) of the flight data recorders and cockpit voice recorders. Typically, the rest of the recorders' chassis and inner components are mangled. The CSMU is a large cylinder that bolts onto the flat portion of the recorder. This device is engineered to withstand extreme heat, jarring crashes and tons of pressure. In older magnetic-tape recorders, the CSMU is inside a rectangular box.
Using three layers of materials, the CSMU in a solid-state black box insulates and protects the stack of memory boards that store the digitized data.
Here's a closer look at the materials that provide a barrier for the memory boards, starting at the innermost barrier and working our way outward:
- Aluminum housing: There's a thin layer of aluminum around the stack of memory cards.
- High-temperature insulation: This dry-silica material is 1 inch (2.54 centimeters) thick and provides high-temperature thermal protection. This is what keeps the memory boards safe during post-accident fires.
- Stainless-steel shell: -- The high-temperature insulation material is contained within a stainless-steel cast shell that is about 0.25 inches (0.64 centimeters) thick. Titanium can be used to create this outer armor as well.
These hardened housings are incredibly important. Without adequate protection, all of the flight data would be destroyed. So to make sure that data stays safe, engineers attack their black boxes with full fury to see if their products can withstand extreme abuse.