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Running to the tail of Boeing's 787 Dreamliner is an umbilical cord carrying a rapid play-by-play of virtually every flight feature.
The data, which totals more than a thousand parameters, is swiftly saved electronically into the flight data recorder (FDR), one of the so-called black boxes that aviation safety investigators say offers critical facts when piecing together an incident, like the mid-air plunge on LATAM Airlines flight 800 earlier this week that injured 50 people.
The FDR and cockpit voice recorder from the LATAM flight should provide evidence to prove or refute the pilot's initial explanation, as relayed by a passenger who spoke to CNN: that cockpit displays briefly went blank and the pilot lost control of the plane.
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It could also show whether the yoke was pushed forward, sending the plane rapidly downward — a scenario The Wall Street Journal reported the investigators are probing, and which may have involved a flight attendant hitting a switch while serving pilots a meal.
"There's absolutely no way this will be a mystery," said Peter Goelz, who led investigations as managing director of the National Transportation Safety Board, and is now a CNN aviation analyst.
"The recorder will indicate if something was starting and what happened."
Regardless of what the FDR shows, the contents of the orange steel box with reflective tape typically mounted in the rear of the plane, which is meant to reduce the risk of damage in a crash, have proven pivotal in past airplane investigations.
Used in past investigations
In 2015, investigators used the FDR to conclude that a pilot of Germanwings flight 9525 deliberately slammed the airliner into a mountain and ruled out potential airplane malfunctions.
The FDR recorded 600 parameters onto a modern memory card and investigators extracted the data despite its exposure to extreme temperatures in the crash.
Sophisticated laboratories like those run by the US National Transportation Safety Board (NTSB), and its counterparts in France, Australia and the United Kingdom, can reconstruct even broken memory cards and then line up the data with audio feeds into the cockpit voice recorder.
The bright orange colour of the container that houses the recorder, a well as locator beacons, help searchers locate the recorders.
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The devices found underwater are typically transported to the lab inside water before being carefully dried, Goelz said.
The 787 Dreamliner — one of Boeing's more recently developed aircraft — feeds data into the flight data recorder through a system called the Common Data Network, which some compare to the human body's central nervous system.
It first flew in 2009 and uses new-at-the-time data transfer technologies.
US regulations specify about 90 parameters that must be fed into the black box.
The list includes the thrust for each engine, temperature, flap settings, and the plane's direction.
International Civil Aviation Organisation standards further specify how often and detailed the data must be.
Altitude, for example, is recorded four times per second and accurate to the half-degree.
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The data now encompasses "every parameter you can imagine — like notes on a musical score," said Kathleen Bangs, a spokeswoman for the aviation tracking site FlightAware, and a former pilot.
"When they take all that data and lay it all together, and put this musical score together, that's when you get really get the full picture."
But the black boxes are not the only tools investigators will have.
Many components of modern planes, such as the engines, also contain computer chips that track detailed data.
Other evidence tools
Automatic Dependent Surveillance-Broadcast (ADS-B) is equipment on aircraft that transmits real-time data including the airplane's position.
The Federal Aviation Administration used this data after ungrounding Boeing's 737 Max in late 2020 to track every Max flight.
Data is also sent to airlines using the Aircraft Communications, Addressing and Reporting System (ACARS), which transmits automated and manually entered messages between airlines and airplanes using radio waves and satellite links.
Some aircraft also carry a Quick Access Recorder (QAR) that is not hardened like the FDR but tracks the same data.
The QAR can be easily hooked up to a laptop and allow airline employees to download plane performance information for analysis.
But it wasn't always this way.
When United Airlines flight 585 crashed shortly before landing in March 1991, the FDR held five data points: direction, speed, altitude, G-force, and whether the radio microphone was keyed to transmit.
When US Air flight 427 crashed three years later near Pittsburgh, the FDR recorded 11 parameters.
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"If these airplanes had been equipped with FDRs with additional parameters, that information would have undoubtedly allowed quick identification of critical control surface movements and their sources and other airplane system conditions that could have been involved in the loss of airplane control," the NTSB said in a 1999 report referencing those two crashes.
"Thus, investigators would have been able to more quickly rule out certain factors, when warranted, and focus on other areas."
The NTSB recommended regulators increase the requirements, which ultimately took effect in the early 2000s.
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Aircraft cockpits may one day contain a new generation of recording devices: video cameras.
The NTSB called for the cameras, saying it could help investigators understand the moments before an incident.
Some unions oppose the cameras, saying there are more effective and less invasive ways to obtain enough data.
US lawmakers abandoned a plan to include a cockpit video camera when crafting this year's expansive FAA legislation.
