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The current flight data recorder (bottom) provides information on 18 parameters of a plane's performance RELATED VIDEO CNN's Ann Kellan reports on the improvements needed to be made to the black boxes on board airplanes Real 28K 80K Windows Media 28K 80K

April 15, 1999
Web posted at: 10:53 a.m. EDT (1453 GMT)

(CNN) -- Flight data recorders are often considered the key piece of evidence when it comes to investigating a commercial plane crash. But they don't always provide the answer.

It took the NTSB 4 1/2 years to determine what caused US Airways flight 427 to spiral into a field outside Pittsburgh because the plane's data recorder didn't provide any information about the rudder system, which turned out to be faulty.

The NTSB says flight data recorders need to be improved and argues the FAA is taking too long to mandate the upgrades.

"The Federal Aviation Administration has not been aggressive enough in the requirement of having state of the art recorders," says NTSB Chairman Jim Hall.

Flight data recorders provide valuable information, from a plane's air speed to the position of the landing gear. Jim Cash, who pulls the boxes, along with the cockpit voice recorders, after plane crashes, says the more information they provide, the less guess work investigators have to do to solve a crash.

"We learn from these accidents," says Cash. "And when we have holes in the data and we don't get that information, it's hard to keep that from happening again. It's hard to learn that lesson that crew and those people unfortunately learned."

Since the US Air crash, the FAA has updated its rules. Flight data recorders on planes built after 2002 will keep an eye on 88 parameters of a plane's performance. But on older planes, they can still watch as few as 18 parameters. The NTSB says that's not enough, calling for flight data recorders on all planes to watch 88 parameters.

The flight data recorder from the 1996 crash of TWA flight 800 in New York

The agency also wants them to be monitored not only after crashes, but as part of a plane's routine maintenance. This is important, in the words of the NTSB's Bob Francis, in order "to monitor the day-to-day safety of airline operations, to keep ahead of incidents that can lead to accidents. We must not wait any longer."

The FAA has instituted a voluntary program, and four airlines -- US Air, United, Alaska and Continental -- now use flight data recorders for safety checks. The NTSB says it's time these checks are made mandatory for all airlines.

CNN's Ann Kellan contributed to this report

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