Historians attribute the invention of the black box to Australian scientist David Warren in the 1950s. Investigators plan to push forward on Friday with efforts to retrieve the two aircraft involved in a crash in Washington that killed 67 people and raised questions about air safety in the U.S. capital. Fresh from recovering the so-called black boxes from the American Airlines plane that crashed into the Potomac River after colliding with an Army Black Hawk helicopter on Wednesday, divers aim to “salvage the aircraft” and find additional components on Friday, Washington’s fire department said.

“Overnight, boats will remain on scene for security and surface searches from local, state, and federal regional partners,” it said. The black boxes have been recovered from the American Airlines Bombardier CRJ-700 regional jet, which collided with a U.S. Army UH-60 Black Hawk helicopter and crashed into the Potomac River on Wednesday, killing 67 people. Lead investigator Brice Banning said on Thursday that the helicopter also contained “some form of recording devices” that would be read either by the National Transportation Safety Board or by the Defense Department under existing agreements.

They are not actually black but high-visibility orange. Experts disagree how the nickname originated but it has become synonymous with the quest for answers when planes crash. Many historians attribute their invention to Australian scientist David Warren in the 1950s. Earliest devices recorded limited data on wire or foil. Later devices switched to magnetic tape. Modern ones use computer chips inside hard casings.

There are two recorders: a Cockpit Voice Recorder (CVR) for pilot voices or cockpit sounds, and a separate Flight Data Recorder (FDR). Some devices combine both functions. They are mandatory on civil flights and the aim is to preserve clues from cockpit sounds and data to help prevent future accidents, but not to determine wrongdoing or liability. In broad terms, investigators say the FDR helps them analyse what happened and the CVR can - though not always - start to explain why. But experts caution that no two probes are the same and virtually all accidents involve multiple factors.

The disappearance in 2014 of Malaysian Airlines MH370 triggered debate about whether data should be streamed instead. They weigh about 10 pounds (4.5 kilos) and contain four main parts:. After contact with water, they must first be thoroughly dried and the connections cleaned to ensure data is not erased accidentally. Audio and data files are downloaded and copied. The data itself means little at first. It must be decoded from raw files before being turned into graphs and synchronised with other data, like air traffic control transmissions.

Lab experts sometimes use “spectral analysis,” a way of deciphering fleeting sounds or barely audible alarms. FDRs must record at least 88 essential parameters but modern systems can typically track 1,000 or more additional signals. The CVR usually contains two hours of recordings on a loop and this is being extended to 25 hours. Implementing such regulatory changes can take years, a delay highlighted by the crash last month of a Jeju Air Boeing 737.

The recorders in that accident, in which 179 people died, did not capture the last four minutes of flight, officials say. A spate of accidents in the 1990s in which recorders had stopped working when power was lost led the NTSB to recommend enough backup power to provide 10 minutes of extra recording. The change was finally adopted for new planes delivered from 2010, but only came into effect eight months after the 737-800 involved in the Jeju crash left the Boeing factory, according to aircraft data on Flightradar24.