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RF Terrorism ~~
A Menace of the 90's

January, 1994

Executive Summary

The United States has been a terrorist target for decades. 1993 saw the successful attack of the World Trade Center, the elaborate planned bombing of several other high profile targets in New York and an international assassination plot against former President Bush. With the arrest of Sheik Omar Abdel Rahman and the prosecution of his followers in these attacks, terrorism experts speculate that attacks against the U.S. may increase. At the same time, a weapon is now available to subversive organizations against which we have no defense. In fact, apart from the catastrophe itself, the weapon will leave no evidence of the attack.

This new addition to terrorists' arsenal is the Radio Frequency (RF) Weapon, sometimes called a directed energy weapon. An RF Weapon uses high power microwave energy to disrupt victim electronic systems. The RF energy is aimed at the victim by using a directional antenna, similar to that used by a radar. Another similarity between an RF Weapon and radar is the inability for a target to tell it is being "illuminated" without detectors.

These weapons have proven successful against a wide range of victims. The vulnerability of an electronic system is directly proportional to its degree of sophistication and use of modern microprocessor technology. For example, while antiquated systems using vacuum tubes are almost impossible to victimize using this technology, modern computers are easily disrupted.

The importance of the victim system, and therefore its attractiveness as a terrorist target, is dependent on its intended purpose. Causing a malfunction in a sophisticated video game may annoy the player, but will be of little value to a subversive. On the other hand, interfering with critical control systems for "fly by wire" aircraft will have more catastrophic results.

The airline industry is at particular risk. Although there are many potential targets against which this new weapon could be used effectively, civil aviation has some unique liabilities. First, airliners are a historically favorite target for subversives. Second, and most importantly, the airlines have begun advertising their vulnerability.

The recent publicity of disruption in aircraft navigation and control systems by passenger's laptop computers highlights the vulnerability of these systems to non-ionizing radiation. The press further amplified the public awareness of the ability to disrupt modern aircraft without leaving any residual evidence. Articles published in open literature have discussed the effects of RF emissions on airliners.

There has already been at least one crash whose cause cannot be explained by the National Transportation Safety Board (NTSB). Data published by the NTSB are consistent with an attack using this new weapon. Besides the crash of United Airlines 585, the NTSB suspects high power RF energy may have caused several sudden and dramatic disruptions of aircraft autopilot systems.


Advanced electronic systems are increasingly vulnerable to upset by electromagnetic radiation. Many Department of Defense (DoD) and Department Of Energy (DOE) studies indicate Radio Frequency (RF) power is a threat to the proper operation of modern systems. As circuits have become more densely packaged, more energy efficient and operate at higher speeds, they have experienced an associated increase in vulnerability and susceptibility to perturbations from non ionizing radiation.

This inherent vulnerability to RF power has spawned international research in optimizing transmitters for use as weapons. RF Weapons have been developed by NATO and former Soviet nations. These weapons are designed to exploit this inadvertent vulnerability to RF power by concentrating as much power as possible into a controlled field. This has proven very effective, and anecdotal data suggest successful combat deployment.

The effects of a successful RF Weapon attack are unpredictable. The primary goal is merely disruption of the victim system, the results of which are of secondary importance. Consequently, the result varies widely depending upon the victim system. In some cases, computers may be reset. In other cases, local oscillators may be driven off frequency, navigation systems misguided, safety sensors incorrectly set or reset, faulty data recorded and control systems given erroneous inputs.

The significance of the perturbation is proportional to the importance of the system corrupted. A portable compact disc player may react by garbling music or changing the track it was playing. A similar amount of energy directed at a commercial aircraft could corrupt the plane's control and navigation systems enough to cause a crash.

Another important similarity shared by vulnerable systems involves post-attack evidence. Typically, there is none. Although the perturbation of the victim system is indisputable while subjected to the RF field, the affected circuits are rarely permanently damaged. This makes identification of the cause extremely difficult. Failures appear to be anomalies with no traceable cause. An interesting aspect of a successful RF Weapon attack is that no evidence remains to incriminate the perpetrator.

Airline Vulnerability

The effects of even low level electric fields have long been recognized by the civil aviation community. Regulations prohibiting airline passengers from using radio receivers in flight are in response to the threat such systems pose to the plane's electronics systems. Super heterodyne receivers, such as those in commercial AM/FM radios, contain small oscillators which generate RF energy. Signals generated by the oscillators are very small. Signals escaping the radio as RF energy are unintentional and therefore likely to be smaller still. Even these very small RF signals threaten the stability and reliability of the aircraft's electronics.

As aircraft become more advanced, their vulnerability increases. As aircraft electronics become more integral with the actual control of the plane, the results can be more catastrophic. Boeing claims that their 757 can take off, fly to its destination and land itself without pilot intervention if necessary. The plethora of gauges formerly found in the cockpit has been mostly replaced by a single screen. On board computers decide what information the pilot needs to see displayed on the screen. The moment-to-moment decisions in flying the plane have been shifted to the built-in electronics. Disrupting these systems can cause the plane to execute erroneous commands resulting in a crash. Jets manufactured by Airbus are even more advanced, with computers overriding pilot decisions in many cases.

Laptop computers, portable video games and other electronics used by passengers in flight have been linked to flight control anomalies. Similar to an attack, no evidence of the disruption remains for analysis after the interfering signal stops. This has made locating failures very difficult. Cockpit personnel have resorted to going through the cabin and asking individual passengers to turn off their computers and games. Correlating the aircraft's return to normal operation with the disabled carry-on has been the most powerful tool in identifying the source of the problem.

RF Terrorism

RFWeapons are an ideal tool for terrorists. They present a combination of (1) a proven vulnerability in one of terrorists' favorite targets-airliners; (2) ground based systems can allow a non-suicidal attack; and (3) cause for the attack cannot be identified.

Recent restrictions of personal electronic devices (PEDs) during approach and takeoff advertise when the aircraft is at greatest risk. Coincidentally, it also represents the terrorist's greatest opportunity. If on board systems are affected by inadvertent PED emissions of fractions of watts, an attack focusing billions of watts on the plane may also disrupt the systems. During approach and takeoff, vulnerability is increased by low airspeed and altitude. Pilots have less time to react to system failures and have fewer options. During this critical phase, the planes are over uncontrolled ground and at close range, providing terrorist access.

Washington's National Airport presents a prime example of a terrorist target. Many aircraft approach the airport along the Potomac River. As they pass over the Francis Scott Key Bridge, they have altitude and airspeed consistent with final approach. The banks of the river, as well as the Key bridge, are uncontrolled. The bridge has several traffic lanes, and pedestrian lanes on both sides. The river offers an unobstructed view of approaching aircraft from many vantage points.

A terrorist can set up a portable RF Weapon on the bridge or river bank attacking planes as they pass over. If successful, the victim aircraft may suddenly and inexplicably fall into the river. A successful attack will result in a crash, leaving no evidence of sinister involvement.

Figure 1

Figure 1 depicts the illumination of the victim airliner with an RF Weapon. Since the terrorist is able to remain on the ground and out of the sterile environment of the airport, he can conduct his attacks without risk of injury or apprehension.

The lack of residual evidence is critically important to terrorists. It increases the probability of success for subsequent attacks, since potential targets will not be able to identify the risk against which they must protect themselves. At the same time, it decreases the probability of apprehension during any attack.

Presidents Reagan and Clinton have sent strong messages to subversives, in the form of air strikes and cruise missile attacks, that the United States will not tolerate terrorism. An unintended message was also sent, that if one is to attack US interests, there must not be residual evidence linking them to the crime. RF Weapons provide the insulation of deniability.

The most recent outbreak of terrorist activity has been based more in religion than nationality. Islamic Fundamentalists view the United States as "The Great Satan." Unattributable catastrophes affecting U.S. assets can be very useful when linked to an angry deity.

By then publicly predicting another such attack, perhaps at a different airport and as a prophecy of their deity, the terrorist organization achieves their primary goal. They will have caused societal panic. The ripple effects of crippling commercial aviation will be international. There will be no way to prevent future attacks or even know when they have occurred apart from the catastrophes they cause. The world will be hostage.

This technology represents a unique opportunity for religion-based terrorism. While there is no evidence left whereby the subversives can be prosecuted, they can take credit for their acts by predicting them in advance.

Terrorist Cognizance

During the Soviet attempt to conquer Afghanistan, the United States provided significant support to the aggressor's enemy, the Afghan Mujahedeen. The Mujahedeen was composed of Islamic fundamentalists recruited worldwide. Once in Afghanistan, they were armed with western weaponry and saw the effects of Soviet weapon systems. It is reasonable to assume that usefulness of RF Weapons in the Soviet arsenal was demonstrated to the Mujahedeen.

The same factions that formed the Mujahedeen fighting the Soviet invaders are now focused on the United States. Indeed, the definition of Mujahedeen is "Moslem guerrilla warriors engaged in a jihad." A jihad is defined as "A Moslem holy war or spiritual struggle against infidels." The same Mujahedeen that launched their jihad against the Soviet Union in the 1980's now has targeted the U.S. as the subject of their jihad of the 1990's.

The present jihad is fought by different rules, though. It is fought through carefully planned terrorist attacks against unsuspecting American civilians instead of military targets. Islamics have witnessed technology that will cause a major catastrophe that can be denied by the perpetrators and instead attributed to Allah's wrath.

RF Weapon Availability

Having shown the effectiveness of an RF Weapon and why a terrorist would want to use it, how difficult is it to procure? Clearly there are a number of weapons of mass destruction that terrorists would like to use, but are controlled by the sane powers in the world. This is generally done by tightly limiting access to critical technology or components. In some cases, the weapon system is too expensive or visible for a subversive organization to procure.

None of these safeguards are applicable to RF Weapons. The technology was explored on both sides of the iron curtain under strict security for some time. The technology has recently moved into the physics labs of universities in the West. This provides a subversive organization with the opportunity to learn how to build such a system from scratch, using no controlled components or subsystems.

More recently, an even greater opportunity emerged. The former Soviet Union is selling its technology on the open market. In June 1993 a large sale in London reportedly featured many technologies that had been closely guarded secrets. A subversive no longer needs to learn how to build a weapon. A tested weapon is probably available for use. Soviet scientists who lost their jobs in their government's demise are also plentiful. Politically biased against the U.S., they can serve as instructors and/or system operators.

On March 3, 1991, United Airlines flight 585 crashed on approach to Colorado Springs. The NTSB has not been able to determine a cause for the crash. Their studies show the controls responded erratically and they are unable to reproduce the conditions of the crash in a simulator. Pilot autopsies and cockpit voice recordings indicate that the flight crew was competent and actively responding to the malfunctions. These are the exact indications an RF Weapon attack might cause and the same residual evidence in the aftermath. The only element missing is a terrorist organization claiming credit.

While UAL 585 may have crashed for reasons other than an RF Weapon attack, it serves as an illustration of how such an attack would look. The flight crew had complete loss of control of the plane. Something besides pilot input caused the plane to bank sharply and crash in an almost directly nose-down attitude. Data show the plane pulled 3g's in turning and was actually headed slightly in the opposite direction from its intended path when it crashed.

UAL 585 is the only airline crash the NTSB has been unable to solve. Coincidentally, it occurred during the Persian Gulf war, when the threat of terrorist attacks against airlines was perceived to be at its peak.

A year before UAL 585 crashed, a SECRET paper entitled "RF Weapons in the Hands of Terrorists-Threats and Countermeasures" was published. It described how an attack would look, the probable results of an attack, and the evidence that would be left behind. The crash of UAL 585 closely mirrors these descriptions published a year before the incident.

Independent Reviews

The problem described in this paper has been carefully reviewed by many independent experts. These include representatives of the Air Force, Army and Department of Transportation. None have disagreed with any of these assertions, nor with the solutions proposed by TES.

A more comprehensive, classified, paper has also been reviewed by intelligence organizations. While their specific comments are not appropriate for inclusion in this document, there was no disagreement with the issues discussed here.

After the bombing of Pan Am 103, the President's Commission on Aviation Security & Terrorism reviewed airline safety. Their recommendations resulted in Public Law 101-604 "The Aviation Security Improvement Act of 1990." That law requires aviation security against terrorism be given the highest priority by the U.S. Government. The Commission found emerging threats to be specific concerns, based on the government's demonstrated lack of attention until the loss of life. RF Weapons are precisely the type of emerging threat that frightened the Commission.


The threat of RF Weapons against airliners and other targets has devastating potential. Without exaggeration nor dramatization, the technology exists to allow terrorists to make a series of planes crash one after another, without having to "reload," with no apparent cause. The technology also exists to counter this threat. But it must be developed and fielded with the priority reserved for it by law.