Since the Sept. 11 tragedy there has been an obvious emphasis on increased airline security. Part of the process is finding out exactly what happened on the hijacked planes and how it happened. Central to this investigation is finding the so-called 'black boxes''the flight data recorder, which records up to 50 aspects of the plane's flight, and the cockpit voice recorder. The workings of these devices are not often explained, but are actually similar to commonly used household items.
Starting in the post-World War II era, flight data recorders became a permanent facet of commercial and private flights, with the purpose of recording information about aircraft operation, such as fuel expenditure and elevation. The first black boxes used magnetic tape like that in any tape recorder. Mylar tape was pulled across an electromagnetic head, which imprinted data on the tape that was fed in from several areas of the plane. The tape was bulky and could not stand up to adverse conditions, such as extreme heat.
Now, instead of magnetic tape, the black boxes have solid-state memory boards like those found in any computer. These are simply a series of memory chips that are fed information from throughout the plane. With the amount of memory these chips can hold, there is unlimited potential for what data can be stored.
The modern black box draws power from the plane's engines by way of two generators. Each of the generators goes to a separate box. Several built-in cockpit microphones pick up the cockpit voices and any ambient noise such as switches or thuds. Information on engine speed, landing gear, flap position and others are constantly filtered into the chips, giving a full record of the flight. Even if there was no indication of distress on a plane previous to a crash, with the capabilities of the new memory boards, odds are the black boxes will be able to show what went wrong.
The determining factor for the amount of recovery possible'and what is feared to have gone wrong in the case of the Sept. 11 planes'is the amount of damage the black box can sustain. Black boxes are placed in the tail of the plane for initial protection.
'The whole front portion of the airplane provides a crush zone, which assists in the deceleration of tail components, including the recorders, and enhances the likelihood that the crash-protected memory of the recorder will survive,' said Frank Doran, director of engineering at L-3 Communications Aviation Recorders.
When an impact occurs, the boxes must be able to survive immense pressure, severe throttling, fire and flooding. A shell of aluminum, covered by inch-thick, high-temperature insulation, and encased by a quarter-inch stainless steel shell, has proven able to protect the boxes under almost any conditions. If a plane is lost underwater, a beacon sends a 'ping' signal for 30 days to help rescuers find the boxes. On top of all this, there are new ways to protect the boxes which are being tested constantly.
While the boxes are nearly indestructible, it is feared that the intense heat produced by the fires burning in the World Trade Centers towers may have damaged the boxes on those planes, but that has yet to be determined. If they are recovered, they will certainly provide needed evidence to help guard against future terrorist attacks.
