Crash investigators can't see inside the cockpit of a doomed airliner, because commercial aircraft don't have crash-proof video recorders. Not yet, anyway.
And investigators can't tell what happens to flaps and rudders once an airplane starts to disintegrate, because the "black boxes" that record such information don't have redundant power supplies to keep them working when a plane crumbles. They probably will soon.
Even without those more futuristic innovations, the EgyptAir jetliner that crashed off the coast of Rhode Island on Halloween was equipped with one of the most sophisticated flight-data recorders in the air -- one designed to show what 55 different aircraft systems were doing when the plane failed.
Assuming the device worked as designed, investigators will know what the plane's engines and flaps were doing when the jetliner crashed. They will know its speed, altitude and temperature -- even whether the pilots were using certain controls.
Modern flight-data recorders are devices born of frustration. Frustrated by the lack of information left behind to determine the cause of plane crashes, federal investigators demanded improvements in the recorder, commonly known as the "black box."
In two crashes of Boeing 737s, the National Transportation Safety Board suspected a flaw in the plane's rudder design. But the recorders on those planes captured only 11 pieces of information -- all that was required when they were built. So modern recorders are made to tell more.
Flight-data recorders have been around literally since the beginning of powered flight. The Wright brothers crafted a device to automatically record time, distance and the number of propeller revolutions, and used it for their pioneering flight in 1903.
The federal government has required some type of flight-data recorder on commercial aircraft since 1958, when the Civil Aviation Authority ordered planes to have a "crash-survivable" device on board to record altitude, airspeed, heading and flight duration.
Today, commercial aircraft are required to carry two so-called "black boxes" -- and they aren't black. They're blaze orange, making them easier to locate after an accident.
One box -- the cockpit voice recorder -- records voices and sounds inside the airplane's cockpit. It often provides the most dramatic and disturbing details about what caused a plane to fail.
The second box typically provides the most hard evidence for investigators. The flight-data recorder can receive data from hundreds of systems throughout the airplane, recording how flight controls are moved or whether engines are working.
By Aug. 18, 2002, new commercial aircraft must be built with flight-data recorders that monitor 88 different pieces of information. With those new recorders, investigators will know things such as what position the flaps and rudders were in, and whether the placement was done by the pilots.
But lesser flight-data recorders will still be in the air. Older aircraft are not required to have recorders as sophisticated. Improvement of the data recording system would require more than simply changing the box. To record more information, the plane have to be wired with the monitoring devices that send the information to the recorder.
The law governs more than the device's ability to record data -- it must also survive a crash.
A typical flight data or voice recorder is encased in an orange sheet-metal shell. The outer casing and most of the electronics within it are usually smashed or mutilated by the forces of an airplane crash.
But the outside of the device is of no use to crash investigators. The crucial component of a flight recorder is the recording medium -- usually either a magnetic tape or a computer chip -- and manufacturers go to great pains to ensure that it survives intact.
The recording devices are required to withstand an impact equal to 3,500 times the force of gravity. They must survive 1,100-degree heat and water pressure equivalent to a depth of about four miles.
At AlliedSignal Aerospace, which manufactured the recorder on board EgyptAir Flight 990, technicians test the devices by shooting them from a pneumatic cannon at a fixed barrier. To test puncture resistance, a 500-pound weight is dropped on the data-storage device from 10 feet, with the weight concentrated on an impact point 1/4-inch wide. The units are burned, submerged in jet fuel and pressed with 5,000 pounds of force for five minutes.
New flight-data recorders have solid-state components with few or no moving parts, and often come with cockpit voice recorders included in the same unit. Airlines might soon be required to have two voice/data recorders on each plane -- one hidden in the tail where most recorders are kept, and another near the cockpit, closer to the most crucial information.
"They've changed dramatically," says Ron Crotty, a spokesman for AlliedSignal. "About the only thing that hasn't changed is that people still call them black boxes. I'm not sure why they do. I've asked everybody I can find in our company how that got started, and we don't know."