After a Crash
Although they are called "black boxes," aviation recorders are actually painted bright orange. This distinct color, along with the strips of reflective tape attached to the recorders' exteriors, help investigators locate the black boxes following an accident. These are especially helpful when a plane lands in the water. There are two possible origins of the term "black box": Some believe it is because early recorders were painted black, while others think it refers to the charring that occurs in post-accident fires.
Underwater Locator Beacon
In addition to the paint and reflective tape, black boxes are equipped with an underwater locator beacon (ULB). If you look at the picture of a black box, you will almost always see a small, cylindrical object attached to one end of the device. While it doubles as a handle for carrying the black box, this cylinder is actually a beacon.
Photo courtesy L-3 Communication Aviation Recorders
A close-up of an underwater locator beacon
If a plane crashes into the water, this beacon sends out an ultrasonic pulse that cannot be heard by human ears but is readily detectable by sonar and acoustical locating equipment. There is a submergence sensor on the side of the beacon that looks like a bull's-eye. When water touches this sensor, it activates the beacon.
The beacon sends out pulses at 37.5 kilohertz (kHz) and can transmit sound as deep as 14,000 feet (4,267 m). Once the beacon begins "pinging," it pings once per second for 30 days. This beacon is powered by a battery that has a shelf life of six years. In rare instances, the beacon may get snapped off during a high-impact collision.
In the United States, when investigators locate a black box it is transported to the computer labs at the National Transportation Safety Board (NTSB). Special care is taken in transporting these devices in order to avoid any (further) damage to the recording medium. In cases of water accidents, recorders are placed in a cooler of water to keep them from drying out.
Photo courtesy U.S. Department of Defense
U.S. Navy Lieutenant Junior Grade Jason S. Hall (right) watches as FBI Agent Duback (left) tags the cockpit voice recorder from EgyptAir Flight 990 on November 13, 1999.
"What they are trying to do is preserve the state of the recorder until they have it in a location where it can all be properly handled," Doran said. "By keeping the recorder in a bucket of water, usually it's a cooler, what they are doing is just keeping it in the same environment from which it was retrieved until it gets to a place where it can be adequately disassembled."