The Investigation Into the Fall
of Pan Am Flight 103

Paul C. Janzen

November 21, 1995

On December 21, 1988, Alan Topp, an air traffic controller in Prestwick, Scotland, was tracking the progress of a 747 jetliner flying more than 31,000 feet above nearby Lockerbie. Suddenly, four bright blips flashed across his radar screen; then the screen went blank. Minutes later, the wreckage of Pan Am Flight 103 and the bodies of its 259 passengers began to fall to the ground. The accident killed all the passengers and eleven residents of Lockerbie, making it the worst aviation disaster in British history [Emerson and Duffy, 1990]. The explosion spread wreckage from the plane over a 1000 square mile area, and more than one thousand workers helped collect bodies and pieces of the plane [Brown, 1989]. From the collected wreckage, investigators determined that a terrorist's bomb had caused the disaster. They also identified the location of the bomb on the plane, the suitcase that contained the bomb, and the type and country of manufacture of the explosive. They even concluded that the bomb was hidden in a Toshiba "Bombeat" stereo [Emerson and Duffy, 1990].

 The investigation into this disaster is important for several reasons. First, it is a fascinating application of the scientific method. For instance, investigators looked at small holes in the metal members of the aircraft caused by hot explosive gases. This information helped pinpoint the exact location of the bomb in the plane [Emerson and Duffy, 1990].

The investigation of the crash of Flight 103 is also important because rarely can authorities study the explosion of an airplane in as much detail as they could the explosion of Flight 103. Most terrorists set their bombs to explode over water, destroying virtually all evidence [Emerson and Duffy, 1990]. Furthermore, politics sometimes prevents government agencies with the most accurate tools for conducting forensic investigations from participating in the investigations. For instance, in August 1988, a Pakistani jet crashed with the Pakistani president and the US ambassador to Pakistan aboard. The State Department and the Department of Defense convinced the White House that the presence of the FBI would not "add any expertise to the team [already investigating the crash]" [Emerson and Duffy, 1990]. The investigation was mishandled, and the final findings were never publicly released. However, in the Flight 103 investigation, the FBI and other United States and British authorities used their advanced scientific methods for analyzing the crash.

 Last, the inquiry into the bombing of Flight 103 is important because of the prevalence of terrorism. Between 1980 and 1988, terrorists killed more than six hundred Americans [Emerson and Duffy, 1990]. Also, the 1991 Persian Gulf War significantly increased the risk of terrorism around the world [Masland, 1991]. The inquiry into the bombing of Flight 103 provided much valuable information about the methods of modern terrorists. As a result of this information, airlines have made significant changes to their security measures. Furthermore, recommendations have been made to airplane manufacturers about ways to lessen the effects of explosions [Shifrin, 1990].

 This paper will emphasize the scientific techniques used to reach conclusions based on evidence gathered from the crash. It will cover, first, the methods that authorities used to collect more than ten thousand pieces of debris, and, second, how they kept track of all those pieces. The third section will discuss how authorities came to conclusions about the explosion and the responsible terrorists from pieces of wreckage. It will discuss how authorities determined the design of the bomb, its placement and packaging, and how the bomb escaped airline detection systems. Authorities' inferences about the plane's mechanical failure as a result of the explosion will be presented. The conclusion of the paper will review the changes in airport security and the recommendations for changes in airplane construction that resulted from the investigation, as well as theories about who was responsible for the bombing.

 When the bomb aboard Flight 103 exploded, it sent thousands of pieces of debris to the ground. Authorities knew that it was important for them to recover and analyze as many pieces of debris as possible so that they could reach conclusions about the bomb and its creator.

 The recovery phase of the investigation was by no means easy. Winds aloft of over 100 miles per hour spread debris over an area around Lockerbie of almost 1000 square miles. The task was also difficult because much of the area around Lockerbie was heavily wooded and nearly inaccessible by foot. Despite these problems, this phase was remarkably successful„ more than ten thousand pieces of debris were recovered [Emerson and Duffy, 1990]. Techniques that authorities used to recover the debris can be classified into three groups: ground-based methods, air-based methods, and space-based methods.

 The main way authorities recovered the debris from the explosion was by a ground search. The search area was divided into twelve sections of about eighty square miles each, and authorities assigned each of the one thousand volunteers, police, and soldiers to one of the areas. The searchers were further divided into search parties of eight to ten people. Each search party walked across the areas assigned to it, picked up anything that might have been on the plane, and placed it in bags. They were told, "If it's not growing and it's not a rock, pick it up" [Emerson and Duffy, 1990].

 One of the problems that the search parties faced in the early stages of the recovery phase was poor communication. Groups of police could not communicate with groups of soldiers, because their radios operated on different wavelengths. Therefore, search parties frequently either ran into each other or retraced the steps of other groups. To solve this problem, authorities assigned an amateur radio operator to each search party. Each radio operator carried a map of the area, tracked the progress of his party, and coordinated the other search parties in the area.

 This ground search was an effective tool for collecting debris from the explosion. Once, the coordinator of the investigation was helping a search party look for clues in a marshy area. He was wearing an earphone to hear radio transmissions from other search parties. He bent down to pick up a piece of debris, and the earphone fell out of his ear. The earphone sank into the marsh, and he could not find it. Several days later, he was inspecting a bag of debris collected from the same area. Most of what he found in the bag was the same stuff he had been looking at for weeks: bits of clothing, pieces of the plane. Then he found the earphone he had dropped days before. He had not been able to find it when he knew where he had dropped it, yet a search party had found it [Emerson and Duffy, 1990].

 To help find debris in heavily wooded areas, authorities used helicopters and aerial infrared photography. At first, British military helicopters flew over the crash site and pointed large pieces of wreckage out to search parties on the ground. However, these helicopters were much too large to maneuver close to heavily wooded areas to find more well-hidden wreckage. Later in the search, authorities requisitioned smaller, private helicopters, which could fly low enough to identify pieces of debris. Also, airplanes took infrared photographs of the crash site. The infrared light penetrated trees and underbrush to "see" wreckage. The military uses similar techniques to see objects at night.

 Several satellites served the same purpose as the airplanes with the infrared cameras to find debris in heavily wooded areas. Within hours of the crash, a French satellite delivered photographs of the area around Lockerbie to searchers. Although these photographs showed some larger pieces of debris in wooded areas, the images did not have the resolution that authorities needed. They tried to enhance the detail of the photos with computers that improved contrast and resolution, but they still could not get the level of detail they needed. Later in the search, the Defense Department and NASA arranged for sophisticated spy satellites to photograph the area. These satellites can read the text of a newspaper on the earth from several miles in the sky, and they provided more than enough detail to find debris in the most heavily wooded areas [Emerson and Duffy, 1990].

 As the wreckage was collected from the ground around Lockerbie, it was placed into clear plastic bags along with other debris from the same search area and brought to a school gymnasium in Lockerbie. Each piece was x-rayed and checked for residue from the explosive. Then, every relevant detail about the piece of debris was entered into a computer. The computer, known as HOLMES (Home Office Large Major Enquiry System), was specifically designed to keep track of this kind of information. Technicians recorded information such as the color of the item, its description, and where it was found in the HOLMES computer [Emerson and Duffy, 1990].

 After technicians entered details about the piece of debris into the computer, the piece was classified as either a passenger's possession or a piece of the airplane. If it was a possession, police photographed the item. These photographs served two purposes. First, they served as a permanent record of the item. Second, they allowed the families of the passengers to avoid having to identify the actual torn, soggy possessions of their loved ones. When the item was linked to a certain passenger, it was placed in a large cardboard box with the other possessions of that passenger [Emerson and Duffy, 1990].

 If the item was a piece of the airplane, it was taken to an empty airplane hangar several miles from the crash site, where technicians slowly reconstructed the Boeing 747. Some said that it looked like "a spooky phoenix rising from the ashes" [Emerson and Duffy, 1990]. By reconstructing the plane in this way, forensic specialists could tell how the plane came apart 31,000 feet above the earth's surface.

 The recovery and cataloging phases of the investigation into the fall of Pan Am Flight 103 were certainly important, and these two phases took much of the time and energy of investigators. However, the next phase (reaching conclusions about the bomber and his methods) was the focus of both the scientific and the political investigations. As the investigation continued, the political and scientific aspects of the search for the terrorist strongly influenced each other. For instance, the CIA suspected that an East German communist group had planted the bomb. They instructed forensic specialists to test the bomb fragments for explosives frequently used by that group [Emerson and Duffy, 1990]. To a much greater degree, however, the scientific investigation influenced the political investigation. Each bit of information that was deduced from the wreckage gave authorities more information about possible suspects.

 One of the first questions officials asked was, "Where was the bomb on the plane?" This information would help determine at which airport the bomb boarded the plane. In the early part of the investigation, authorities directed most of their efforts toward answering this question. During the explosion, pressures and temperatures inside the cargo hold of the plane reached enormous levels. Temperatures and pressures of this magnitude cause certain changes in the metal of the plane. Forensic analysts made an estimate of the location of the bomb by studying these changes.

 First, an explosion like the one on Flight 103 will melt the outer metal skin of the aircraft. The sub-freezing temperatures at the plane's altitude will quench the metal from a very high temperature to a very low temperature. This phase change causes a unique metallographic structure within the metal. Furthermore, the high speed at which the hot gases of the explosion deform the metal causes small holes in the metal.

 Second, a bomb sends thousands of fragments of itself and anything around it hurtling outward at speeds of 1000 feet per second or more. Anything traveling at this velocity will imbed itself in the first thing it hits. So authorities looked for pieces of cargo containers and luggage buried in the frame and skin of the plane.

 When deciding where the bomb had gone off, scientists looked at how luggage came out of the plane. Baggage debris was found in the engines on the right side of the plane; therefore, some investigators concluded that the bomb had exploded on the right side of the plane. They believed that it blew a hole in the right side of the fuselage and sent baggage out that hole. However, this conclusion was wrong. The explosion created tremendous pressure in the cargo hold. The cargo hold failed at its weakest point, as any pressure vessel will. After inspecting more pieces of the plane, technicians concluded that the bomb had been placed on the left side of the plane. The Boeing 747 has a cargo door on the right side, but not on the left. The hinges on the cargo door were the weak point in the cargo-hold pressure vessel, and they were the first to fail. That was how baggage got into the right side engines, but not the left side engines [Emerson and Duffy, 1990].

 Eventually, after looking at enough pieces of twisted metal, analysts concluded that the bomb had exploded just under the "P" in the Pan Am logo outside the plane. They also decided that it had been stored in cargo bay 14L [Emerson and Duffy, 1990].

 After each piece of debris was brought in from the crash site, a device known as a gas chromatograph analyzed its chemical composition. This device told researchers how much residue from the bomb was on that piece of debris, and how close it had been to the bomb. For instance, authorities found an extremely high concentration of bomb residue on certain pieces of clothing. The concentration was so high on these clothes that authorities were immediately certain that they had been around the bomb at the time of explosion. Similarly, the chromatograph indicated that the bomb had been in a copper-colored Samsonite suitcase [Emerson and Duffy, 1990].

 Modern technology has brought the art of bombing far from the days when a bomb consisted of a battery, some dynamite, and an alarm clock crudely wired together. The bomb placed aboard Flight 103 was technologically very advanced. By comparing the chemical composition of the residue to compositions of known explosives, investigators concluded that the explosive was Semtex, a Czech-made plastic explosive. Semtex was ideal for the terrorist's purpose. It has the texture of dough and can be molded into almost any shape. It is nearly impossible to detect by most conventional means, such as dogs and X-ray machines [Emerson and Duffy, 1990].

 Bomb experts could tell much about the construction of a bomb from the tiny fragments of it imbedded in what was around it. The pieces indicated that the bomb had been concealed in a small stereo. Ironically, the stereo the terrorist used was a Toshiba "Bombeat" available only in northern Africa and the Middle East. Authorities also learned much about the bomb from two tiny fragments of the bomb"s detonator. It employed a two-step detonator; the bomb exploded after both detonators were activated. The first detonator was a barometer-detonator that went off when the plane"s altitude caused the barometric pressure inside the cargo hold to dip below a given level. The second detonator was a simple timer. The purpose of the timer was to fool airport security checks. Since terrorists frequently use barometer-detonators, many airports subject luggage to a brief period of low barometric pressure. This process will detonate a bomb not equipped with a timer-detonator before it gets onto the plane [Emerson and Duffy, 1990].

 One of the parts of the bomb that authorities recovered was a microchip from the detonator circuit. This microchip fragment linked the explosion of Flight 103 to explosions investigated in the past. Each microchip is microscopically unique„that is, it has a unique pattern of transistors etched onto it. Investigators found that the structure of the chip they recovered from Flight 103 was exactly like that of one they had found two Libyan agents carrying (along with twenty pounds of Semtex) in Senegal in 1986 [Wright and Ostrow, 1991].

 Authorities began to draw conclusions about exactly how the plane came apart before they took the first piece to the empty hangar. The entire cockpit had fallen in one piece to the ground. The cockpit, nose, and forward cabin were all severed from the rear section of the plane. This pattern of separation was consistent with a bomb stored in the forward cargo hold [Emerson and Duffy, 1990].

 From the collected pieces of plane wreckage, experts were able to tell exactly how the plane disintegrated. The explosive produced a large hole in the fuselage and another in the main cabin floor of the forward cargo hold. The pressure caused by the bomb caused large cracks to develop along the fuselage and floor, even though the aircraft had been specially strengthened to carry military freight during national emergencies. The cockpit, nose, and forward cabin then separated from the rear section of the plane [Shifrin, 1990].

 One of the things that confused investigators in the early part of the investigation was that the pilot had not sent any distress signal. Although the plane began to break up soon after the bomb detonated, authorities felt that the pilot would have had time to send a "Mayday" call. However, when forensic analysts concluded that the bomb had been in cargo bay 14L, airplane experts realized that the bomb had damaged the plane's electronics center. This center receives electric energy from the plane's engines and distributes it to every electronic device on the plane. When the bomb damaged this electrical station, the radios used to send distress signals became useless [Emerson and Duffy, 1990].

 Many relatives of the passengers on Flight 103 flew to Lockerbie to identify the bodies of their loved ones. However, not every body could be identified in this way. To identify these remaining bodies, two techniques were used: dental records and fingerprints. It was difficult to send the fingerprints overseas, because authorities did not have time to wait for couriers, and fax machines did not provide enough resolution to compare to the fingerprints of the bodies. So authorities used a phototelesis machine, which is much like a fax machine, but it transmits images in color and at twice the resolution of a standard fax. Fingerprints transmitted in this way were essential to identifying all the bodies [Emerson and Duffy, 1990].

 By any standard, the bombing of Flight 103 was a terrible disaster, and steps must be taken to assure that it does not happen again. The investigation into this disaster combined scientifically advanced techniques to reach certain conclusions about the terrorist and his methods. The scientific inquiry into the explosion did much to help prevent another explosion of this kind by making recommendations for changes in airplane construction and safety guidelines in airports.

 Recommendations for changes in airplane construction come into two categories: changes in cargo-hold design and changes in flight-recorder apparatus. After reviewing the investigation, the Air Accidents Investigation Branch (AAIB) of the British Transport department recommended that all cargo be contained in stronger cargo holds. Although they admit that such measures could not have prevented the Flight 103 disaster, they feel that stronger cargo containers could make the explosion of a smaller bomb survivable [Shifrin, 1990].

 Most of the suggestions for changes to airplanes, however, concerned the flight recorders. Since the bomb cut power to the flight recorders, they were of no help to the investigation. Part of the problem was that the voice recorders had no power backup. Furthermore, several minutes of recordings are stored in volatile memory (which is erased when it loses power) before being transferred to magnetic tape. Therefore, not only were investigators unable to hear what happened in the plane after the power went out, but they were also unable to hear what happened just before that time. The AAIB recommended that flight recorders have a back-up battery, and that their volatile memory be replaced with non- volatile memory. Also, the AAIB suggested a new instrument that measures pressure changes inside airplane cabins. This device would prove, quickly and conclusively, if a bomb had damaged a plane [Shifrin, 1990].

 Although the proposed changes to airplanes will certainly help reduce the effects of bombs and make the following investigations easier, it is far better to keep bombs off planes in the first place. Therefore, authorities imposed several new security restrictions on airports, particularly those in Europe and the Middle East. First, they insisted that each bag correspond to a passenger, and that if that passenger gets off the plane, his bags go with him. Second, they began randomly searching passengers and their bags. Last, they stepped up plans to install sophisticated devices capable of detecting plastic explosives such as Semtex [Watson and others, 1989].

 Perhaps the most important result of the investigation, however, was that authorities have collected enough evidence to bring the case to trial. The microchip recovered from the bomb's detonator proves conclusively that the regime of Libya's Moammar Gadhafi carried out the bombing; authorities believe that the bombing was in retaliation for the United States 1986 bombing of Tripoli ["Libya," 1991]. Also, the cargo bay containing the bomb held many bags from Malta, a country closely allied with Libya. Although authorities have identified two Libyans as responsible for planting the bomb on the plane, they have yet to extradite them. If they are extradited, justice may be done in one of the worst aviation disasters in history.



 Ambrose, D., Gas Chromatography, 2nd ed. (London: Butterworths, 1971).

 Brown, David A., "Investigators Expand Search for Debris From Bombed 747," Aviation Week and Space Technology, vol. 130, no. 25 (January 9, 1989), pp. 26-27.

 Emerson, Steven, and Duffy, Brian, The Fall of Pan Am Flight 103 (New York: G.P. Putnam's Sons, 1990).

 "Libya Regime Suspected in Pan Am Blast," Austin American-Statesman (June 24, 1991), section A, pp. 1, 4.

 Masland, Tom, "A Tide of Terrorism: Is Saddam's Call to Action a Psy-War Tactic?" Newsweek, vol. 117, no. 24 (February 18, 1991), p. 35.

 Matthews, Robert, "On the Use of Seismometers to Detect the Impact of Meteorites," Quarterly Journal of the Royal Astronomical Society, vol. 31 (1990), pp. 181-189.

 Shifrin, Carole A., "British Issue Report on Flight 103, Urge Study on Reducing Effects of Explosions," Aviation Week and Space Technology, vol. 133, no. 12 (September 7, 1990), pp. 128-129.