And I alone survived
After years of bearing witness to air crashes, the black box is becoming smaller, smarter, and more useful as a safety tool.
Raplee, Assistant Editor
||In the aftermath of the recent
fatal plane crash over the Pacific of Alaska Airlines Flight 261, and other
similar tragedies that have devastated the skies in recent times, a single
piece of equipment carries the hope for answers to the question: What went
wrong? The "black box."
Inside a combination voice and data black box are the digital recording functions to the rear, and power connections and data storage toward the front.
The search for this seemingly indestructible box—which holds the flight data record- er and the cockpit voice recorder—amidst the debris of the wreckage is akin to the quest for the Holy Grail. But in the absence of any survivors or eyewitnesses, it is within these steel walls of the box that the digital recordings of the last few minutes of flight are stored, thus the best prospect for clues to the disaster.
But there is no guarantee that even if found, the black box, which is not black at all, but painted in bright orange for increased visibility, will have the answers. In the case of Egypt Air Flight 990, for example, which went down in October of last year over the Atlantic, air safety officials are still analyzing the muffled recordings.
Although endurance regulations have gone virtually unchanged for several years since the Federal Aviation Administration first required the units on all commercial aircraft, the most notable has been the advent of digital recording technology. Digital recorders can record more parameters over longer periods of time using less energy than older magnetic tape recordings. Today, this kind of information is used not only to investigate an aviation accident, but to increase the safety of flying at a time when air traffic has grown significantly.
The FAA has placed durability requirements on the recorders and their casings to survive severe impact and fire. All aircraft capable of carrying 10 or more passengers for scheduled commercial use are required to have voice and data recorders connected to the electrical power generators of the aircraft's main engines.
The storage medium of each recorder is located in a protective capsule, which must be able to withstand an impact of 3,400gs (3,400 times the force of gravity). Additionally, each must also survive flames at 2,000°F for up to 30 minutes, and submersion in 20,000 feet of saltwater for 30 days. Typically, to increase their chances of survival, the recorders are located in the tail section of the aircraft, which usually sustains the least impact in a crash.
"Most flight data recorders and cockpit voice recorders are constructed with an aluminum sheet metal chassis, and the protective capsule is heat-treated stainless steel or titanium," said Frank Doran, director of engineering for L-3 Communications Aviation Recorders of Sarasota, Fla., one of five manufacturers of black boxes in the United States. "What is attractive to aircraft manufacturers is a recorder that can operate within the requirements while being as small, lightweight, and energy efficient as possible." He said that new solid-state digital recorders have no moving parts and so are smaller and lighter than analog tape devices, and use less power. "This is critical data, and it's important that it be high quality, and that none of it is lost to fire, impact, or loss of power," Doran explained. "That is now possible through advances in technology."
By regulation, the data recorder must monitor and record at least 28 flight parameters, including time, altitude, airspeed, heading, and rates of descent and ascent. Data is recorded on a 25-hour loop. During an accident investigation, the National Transportation Safety Board can use the record of parameters to create a computer-animated video reconstruction of the flight to help determine its cause.
The voice recorder uses four separate audio tracks to record the voices of the flight crew as well as other crucial cockpit sounds, such as engine noise, alarms, and radio weather briefings. Older recorders used analog magnetic tape recording on a continuous 30-minute loop; newer solid-state digital recorders track data over two hours.
The NTSB investigates approximately 2,000 aviation accidents a year. Crash
site investigations are conducted both to determine the cause of an accident
and to pinpoint pilot activity or mechanical modifications that may prevent
similar results in the future. Additionally, these investigations have been
used to determine whether a criminal act was the cause of a crash, in which
case security measures may need to be modified.
In one investigation of a 1987 crash of a Pacific Southwest Airlines flight in San Luis Obispo, Calif., information conveyed over the radio by the flight crew shortly before the crash led to an independent investigation by the FBI. The investigation revealed that a former employee had boarded the plane and shot the flight crew.
Most investigations, however, do not uncover criminal activity. During the investigation of a DC-10 crash in Sioux City, Iowa, in 1989, the NTSB made four differ-ent recommendations before issuing its final report. Within one week of the crash of an ATR-72 aircraft in Roselawn, Ind., in 1994, the Board issued urgent safety recommendations.
Perhaps the most noteworthy investigation was that of TWA Flight 800 in 1996 in the Atlantic Ocean off New York. Once it was determined that an explosion in the center fuel tank may have caused the breakup of the plane, the board issued urgent safety recommendations for the elimination of explosive fuel and air vapors in aircraft fuel tanks.
Recordings of only 30 minutes often lack data critical to an accident investigation. Decisions made by flight crew personnel or other precursory events may occur more than 30 minutes before a crash, which would be erased by newer recording or such a short loop. Also, magnetic tape is less robust, more likely to sustain damage, difficult to service, and has high electrical power requirements. While new solid-state recorders are installed on aircraft built after 1991, the number of older aircraft currently flying cannot be specified. However, the NTSB has recommended a retrofit program for these aircraft as well.
Older recording devices have spawned their share of investigative problems. In the 1994 investigation of a USAir Boeing 737 crash outside Pittsburgh, it was determined that the recording device monitored only 11 parameters of flight information. As a result, the NTSB recommended an immediate upgrade in 737 recorders.
Recording equipment onboard the 1998 Swissair Flight 111 was magnetic continuous loop tape, which apparently cut off six minutes before the aircraft crashed into the waters off Nova Scotia. Investigators also discovered several anomalies in the tapes before both the cockpit voice recorder and flight data recorder shut off, further hampering the investigation.
"Digital recordings are more reliable for a couple of reasons," said Duncan Schofield, engineering manager of flight recorder products at Honeywell International Inc. of Morristown, N.J., which recently acquired Allied- Signal's flight recorder operations. "Voice fidelity is improved on digital recordings; bandwidths are better, and storage of data is easier." Digital recordings can be stored on a chip rather than on large magnetic tapes.
The recovered flight data recorder from EgyptAir Flight 990 arrived at Andrews Air Force Base in Suitland, Md., on Nov. 9, 1999, after it was submerged in 270 feet of water. The flight went down in the Atlantic on Oct. 31.
While recorders are placed in the tail of an aircraft to increase survivability, the distance from the parameters recorded requires long cables running the length of the plane. If the plane begins to break up or power is otherwise severed prior to a crash, recorded data can be lost.
In March 1999, the NTSB made several recommendations to the FAA concerning black boxes. The board suggested that the FAA require a retrofit program after Jan. 1, 2005. In this retrofit, all aircraft carrying analog tape recorders would be furnished with solid-state digital units, which also would feature an independent power source able to support 10 minutes of operating time and engage automatically when aircraft power ceases.
To improve data retrieval, the NTSB has also recommended that all aircraft built after Jan. 1, 2003, be equipped with two combination voice and data recording systems. Both systems should continue to record all mandatory parameters, but one set should be located close to the cockpit and feature an independent power supply, while the other should be mounted in the tail section.
"Redundancy, independent power sources, and longer voice recordings are big steps in making sure data is reliable, detailed, and clear," Schofield noted. "But this information serves greater purposes than merely determining the cause of a crash."
In 1995, the Department of Transportation recommended to the FAA a voluntary Flight Operational Quality Assurance, or FOQA, program. Essentially, the DOT observed that one of the best ways to increase flight safety is for airlines to play an active role in identifying safety threats and take corrective action before hazards lead to accidents.
The FAA is conducting a FOQA Demonstration Study in cooperation with major U.S. airlines. Based on digital flight data recordings, the study provided information on items such as unusual autopilot disconnects, excessive rotation rates on takeoff, unstabilized approaches, and hard landings. It also monitored fuel efficiency, enhanced engine condition monitoring, noise abatement compliance, rough runway surfaces, and aircraft structural fatigue.
Based on the study, the FAA has determined that voluntary implementation of the program is in the public interest because it provides information to help identify areas for safety improvements.
"With all the data available from these recorders, the voluntary FOQA programs are using it in a proactive way," added Schofield. "Now airlines can identify where improvements can be made in areas like flight crew performance, training programs, operating procedures, air traffic control procedures, airport maintenance and design, and aircraft operations and design." He said that quality assurance programs are important tools for the FAA to use to enforce safe practices.
To better facilitate this safety measure, the FAA and NASA have teamed to develop an aviation safety measurement program. Now being developed at NASA's Ames Research Center in Moffett Field, Calif., is an automated performance measuring system planned to monitor 1,200 functions. The resulting database is expected to let researchers generate accurate and meaningful reports for safety analysis. In 1995, Alaska Airlines and NASA agreed to development, testing, and presentation of the system to the Airline Pilots Association and the FAA. The next year, United Airlines signed a similar agreement. Alaska Airlines is testing the system on six MD-80 aircraft.
Once the system is thoroughly tested, plans are for it to service engineering, maintenance, and training at major airlines and at commuter, cargo, and corporate air carriers.
With all of these factors coming together in a little crashproof box, one
other element looms on the horizon. "There is technology for video recordings,"
added LÐ3's Doran. "It's a ways off right now, but I wouldn't rule it
© 2000 by The American Society of Mechanical Engineers