"The aircraft crashed and burst into flames ... Accident investigators are searching for the aircraft's black-box flight recorders."
Similar words are sometimes heard on TV news reports about aircraft accidents. What are these mysterious black boxes and how do they help accident investigators?
Large commercial aircraft are required to carry two separate black boxes or flight recorders - a Cockpit Voice Recorder (CVR) and a Flight Data Recorder (FDR).
The term black-box is a misnomer as the flight recorders are actually painted orange to help in their recovery following an accident.
Flight recorders are also fitted with a battery-powered sonar transducer to aid in underwater recovery (look for the shiny cylinder attached to the front of the recorder).
The data, rather than the whole recorder, must survive the accident so the data storage medium (magnetic tape or microchips) is located within a crash-protected container.
The container is designed to survive both high-speed impact and post-impact fire. Flight recorders are not, however, indestructible and sometimes they are destroyed and the data lost.
Flight recorders are normally located near the aircraft's tail since experience has shown that this area generally suffers the least damage during an accident.
Many accidents have involved aircraft without flight recorders, and despite thorough investigation, the factors underlying these occurrences remain inconclusive or unknown.
On the other hand, accidents leaving very little recoverable aircraft wreckage have been resolved once the flight recorders were found.