black box

A black box is a robust airborne recording device that captures flight data and cockpit communications throughout a flight. Despite its name, the unit is painted international orange to improve visibility in wreckage. Modern aircraft carry two separate units: the flight data recorder (FDR) and the cockpit voice recorder (CVR), though they are sometimes integrated into a single chassis.

The FDR samples parameters continuously, typically at rates between 2 and 25 times per second depending on aircraft type and regulatory requirements. Modern digital systems record 1,000 or more distinct parameters: altitude, airspeed, heading, vertical acceleration, engine thrust, control surface positions, hydraulic pressures, electrical bus voltages, and fuel quantity. Older mechanical FDRs operated at lower resolution and slower sample rates. The CVR simultaneously records all audio from the flight deck: crew voice communications, engine noise, radio traffic, and cabin alerts, typically preserving the last 30 minutes of flight.

Both recorders use crash-hardened construction. The chassis is fabricated from stainless steel or aluminum alloy, typically 3 to 5 millimeters thick, surrounding a robust internal cavity. The recording medium, solid-state memory in current designs, is potted in a silicone compound or enclosed in a protective capsule. The entire unit must survive temperatures exceeding 1,000 degrees Celsius for limited periods, hydrostatic pressures at extreme depths, and sudden deceleration forces. Most designs remain functional after immersion in salt water for extended periods.

Operational requirements and challenges

Black boxes require dedicated electrical power, typically 28 volts DC with backup sources in case main power fails. Data feeds from engine computers, air data systems, and flight control computers must be maintained continuously. Maintenance requirements include periodic functional tests, power supply checks, and data download procedures. Corrosion and connector degradation are common failure modes, particularly in aircraft operated in maritime or high-humidity environments. Many operators establish replacement schedules based on flight hours or calendar age rather than waiting for failure.

Access to recorded data is legally restricted and typically released only to accident investigators, manufacturers, and regulatory authorities. Maintenance technicians rarely have legitimate need to read stored data, though they must ensure the units function and receive uninterrupted power. The term "black box" entered the trade from military radar equipment of the 1950s; the aviation meaning solidified after widespread adoption of FDRs became standard following accidents where investigation was hindered by lack of flight data.