After the search for survivors and recovery of victims in tragic aviation accidents — like that of a UPS cargo plane shortly after takeoff from Louisville Muhammad Ali International Airport in Kentucky last month — comes the search for flight data and a cockpit voice recorder often called the “black box.”

Every commercial plane has them. Aerospace giants GE Aerospace and Honeywell are among a few companies that design them to be nearly indestructible so they can help investigators understand the cause of a crash.

“They’re very crucial because it’s one of the few sources of information that tells us what happened leading up to the accident,” said Chris Babcock, branch chief of the vehicle recorder division at the National Transportation Safety Board. “We can get a lot of information from parts and from the airplane.”

Commercial aircraft have become very complex. A Boeing 787 Dreamliner records thousands of different pieces of information. In the case of the Air India crash in June, data revealed both engine fuel switches were put into a cutoff position within one second of each other. A voice recording from inside the cockpit captured the pilots discussing the cutoffs.

“All of those parameters today can have a very huge impact on the investigation,” said former NTSB member John Goglia. “It’s our goal to to provide information back to our investigators who are on scene as quick as we can to help move the investigation forward.”

This crucial data can also help prevent future accidents. A crash can cost airlines or plane manufacturers hundreds of millions of dollars and leave victims’ families with a lifetime of grief.

But in some circumstances black boxes were destroyed or never found. Experts say further developments such as cockpit video recorders and real-time data streaming are needed.

“The technology is there. Crash worthy cockpit video recorders are already being installed in a lot of helicopters and other types of airplanes, but they’re not required,” said Jeff Guzzetti, aviation analyst and former accident investigator for the Federal Aviation Administration and NTSB. “There’s privacy and cost issues involving cockpit video recorders but the NTSB has been recommending that the FAA require them for years now.”

Watch the video to learn more.

— CNBC’s Leslie Josephs contributed to this report.

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