"Aircraft electrical systems have been implicated in a number of recent accidents and incidents. Since 1983 there were at least 26 well investigated reports of accidents or serious incidents involving electrical interconnect system (wiring) failures, and preliminary findings seem to implicate such systems in the catastrophic crashes of TWA 800 in 1996 and Swissair 111 in 1998." 4

USA TODAY examined wiring problems over an even longer period of time and reported in 2000 that in the previous 24 years, the FAA received at least 259 reports of wire-related smoke or fire on aircraft over 12,500 pounds, a category that includes all passenger jets and most commuter planes. 5

Nonetheless, the FAA doesn't certify wiring for use in commercial airplanes or weed out defective wiring. The FAA has studied and compared wire insulation for more than a decade, but doesn't approve any particular types, leaving it up to aircraft manufacturers to set specifications. Wire performance tests are outlined in a FAA Handbook on Flammable Materials published in 2000 but the tests are voluntary, and the FAA doesn't force the industry to perform them.

The Boeing Company and Airbus, the only manufacturers of large transport planes in the U.S., have opposed making the tests mandatory, Block said. 6 He believes it is because they fear the wiring in their older planes would not pass the tests.

GAO Report on Problematic Wiring

The General Accounting Office (GAO) examined the communication channels the FAA and military services use regarding aircraft safety in a 69-page report entitled "Aviation Safety, FAA and DOD Response to Similar Safety Concerns" (GAO-02-77) issued in January 2002.

The GAO concluded that additional channels of communication are needed between the two to ensure that common safety risks are addressed in a systematic manner. Existing gaps in the processes could allow for communication lapses and delays in getting out critical information in a timely manner.

As a case study, the GAO looked at aromatic polyimide, commonly known by Dupont's trade name Kapton, an insulation material that is used to cover electrical wiring on more than half of the world's nearly 14,000 passenger jets - both older planes and new ones.

The GAO said aromatic polyimide is lightweight, resistance to abrasion and cuts, able to withstand high temperatures, and is flame and environmental resistant, but has two weaknesses:

• Prolonged exposure to moisture alters the chemical composition of this type of insulation and diminishes its integrity, and could cause it to deteriorate.
  
  
• Weakness occurs when two cracks in the insulation develop close together, enabling the current to arc between the cracks at high temperatures. That can cause the insulation to char and carbonize. "This carbonization can turn the insulation into an electrical conductor, and, eventually, can trip a circuit breaker. When a pilot presses the switch to reset a tripped circuit breaker, an entire wire bundle can be disabled and potentially compromise the safety of an aircraft's entire electrical system."

Block said Kapton can explode at 5,000 degrees Fahrenheit, burning everything in its path, even metal fuselage, and he believes it should be banned from commercial aircraft.

Some other wiring experts share his concerns.

Edward Trimble, an investigator for the British government's Air Accidents Investigation Branch, told USA TODAY that Kapton should not be installed on new jets, and older planes found to have numerous cracks in Kapton wiring should be grounded.7

Paradoxically, even though many new planes are built with Kapton wiring, an unidentified senior FAA official told the GAO that the rules that admitted it 20 years ago would prohibit it today. The GAO reported that much more is now known about its limitations, including that it "has the potential to arc track and can contribute to a single event or combination of events that could be a hazard to aircraft." The GAO report further said:

"According to this official, given current knowledge, it would be difficult for FAA to support the use of aromatic polyimide insulation, in its original form, in new aircraft designs. However, this same official noted that while new wire insulation types introduced on the market are likely to have improved performance characteristics, they are also likely to have shortcomings not anticipated at their introduction into service."

Block also thinks the wiring insulation materials PVC, Poly-X and cross-linked Tefzel should be banned from commercial aircraft. Block said about 2,700 commercial planes are wired with PVC;8 about 1,000 commercial planes are wired with Poly-X;9 and about 3,000 commercial planes have cross-linked Tefzel. 10

The U.S. Military and Some Foreign Planes No Longer Use Questionable Wiring

The GAO documented that the FAA and the U.S. military have taken radically different approaches to address wiring. The Navy, Coast Guard, Army and Air Force have all decided, to differing degrees, to remove or not use the type of wire insulator known as Kapton in parts of their aircraft, the GAO reported.11 The Navy took the lead in identifying and examining potential problems and in mitigating hazards after it began experiencing problems associated with Kapton in the mid-1980s, the GAO reported.12

The militaries in England, Canada and Australia have also banned aromatic polyimide from further use. And Australian airline Qantas issued a memo in 2000 prohibiting its mechanics from using Kapton as a replacement wire, citing "ongoing incidents across the world involving Kapton wire." The memo, obtained by USA TODAY, called for purging all Kapton in the airline's inventory.13

The Navy has also removed and banned a wire insulator known as Poly-X from some of its planes and the Air Force removed an insulator known as PVC from some of its planes.

Industry and FAA Response to Questionable Wiring

In response to the Navy's problems with aromatic polyimide, Boeing conducted laboratory experiments in 1985 and 1986 and found that it could simulate arc tracking in Boeing commercial aircraft, according to the GAO. It said Boeing began using a new composite wire insulator known as Teflon-Kapton-Teflon in 1993 for much of its wiring. 14

Some experts say that a composite wire, like any wire, can arc, but when it does, the fire self-extinguishes. The fire goes out because the Teflon in the wire contains fluorine, which is used in fire extinguishers. 15

Block said Boeing uses Teflon-Kapton-Teflon, which he considers the best wiring on the market right now, in its 737 and 757, but uses another wiring insulation called cross-linked Tefzel that is known to be smoky, flammable and toxic on its large twin-aisle transports, the 777, 767 and 747. Boeing originally only used cross-linked Tefzel external to the fuselage (in non-pressurized areas) because of flammability concerns, but in 1993 started to use it across-the-board on the large transports, Block said.

Airbus, meanwhile, uses aromatic polyimide exclusively for wiring inside the fuselage, which is at least 75 percent of the overall wiring used on a plane and equivalent to about 100 miles of wiring, Block said.

The FAA, also acting in response to the Navy's findings about aromatic polyimide, conducted independent research, tracked related research and operational data from industry and the military services, and decided not to mandate its removal from commercial aircraft, the GAO reported. The FAA has not mandated the removal of Poly-X, PVC or cross-linked Tefzel wiring from commercial aircraft, either.

An official with the FAA has informed Block that it is not economically feasible to change out all older wire in aging aircraft. Ronald Wojnar of the FAA's Seattle office wrote a letter to Block in 1996 stating:

'Regarding earlier transport category aircraft, wires used during their construction era may not perform as well as modern types, however, the FAA believes there remains a low level of risk, as can be seen by the continuing outstanding safety record. In most cases, on older aircraft, modifications or changes to the aircraft which involve a wire change requires an upgrade to modern, approved wire. Otherwise, it is not economically feasible to change out all older wire in aging aircraft.''

The FAA has issued advisory notifications to the civil aviation community to help identify and minimize the potential risks associated with the use of some wiring and to describe acceptable practices for aircraft inspection and repair. Block believes the FAA's advisory circulars train mechanics not to make more cracks - but mechanics are not the primary problem. The inherent nature of the wiring insulation material is the main problem, he said. Additional training or advisories will not address the condition of the wires in the current fleet, nor prevent dangerous wires from being used in new aircraft.

In any case, Block believes that industry officials regularly ignore the circulars, particularly warnings regarding the use of aromatic polyimides and the dangers of mixing different wire types in the same bundle due to the potential for arcing and fire.

In 1998, the FAA established the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) to provide recommendations to the FAA on airplane safety issues, including aging airplane electrical wiring systems.16 A report of one of its working groups, which are similar to subcommittees, summed up the status of wiring this way:

"Aircraft systems, including the electrical wiring interconnections, are becoming more and more complex and electrical wires cables and their associated components are becoming increasingly important with respect to airplane systems that are necessary for safe flight. There has been and continue to be many events associated with wire failures. In 2000 the FAA issued 78 airworthiness directives related to electrical wiring. Wire failures are also known to be contributory factors in many incidents and some aircraft accidents. There is concern that existing procedures, directives, and inspections are not sufficient to prevent situations associated with the degradation of aircraft wire."

ATSRAC has found that most discrepancies with wire were in areas of frequent maintenance activity where wiring was unprotected from debris and fluid contamination.

ATSRAC has not recommended the systematic removal of aromatic polyimide or any other questionable wire insulation from aging aircraft. It has identified two items it said that the FAA should pursue to develop options to eliminate or mitigate electrical hazards: arc-fault circuit breakers which can detect and react to an electrical arc much faster than those currently used in aircraft and nondestructive test equipment for aircraft wiring. 17

Block said the committee also decided to recommend improved training and the distribution of more advisory circulars, but not to currently require wires to be tested to see if they will burn or explode. It also decided not to force airlines to check for cracks in wiring by means other than visual inspections even though one of ATSRAC's working groups, using a method other than visual inspection, examined six recently retired aircraft and found cracks in their wiring. The group would not have found the cracks if it had only done visual inspections, Block said. He said it takes only one crack to ignite fuel vapors, flammable insulation blankets or to send an uncommanded input to an autopilot to send it out of control.

"The sad reality is that currently the only way we have of finding a crack in a wire is to visually inspect it," Block said.

In August 2001, the FAA announced that it had undertaken a new initiative, the Enhanced Airworthiness Program for Airplane Systems, in cooperation with industry officials. The FAA says the initiative is intended to:

• Enhance the safety of aircraft wiring from design and installation through retirement.
  
  
• Increase awareness of wiring degradation.
  
  
• Implement better procedures for wiring maintenance and design.
  
  
• Ensure that the aviation community is informed.
  

Summary of POGO's concerns about airplane wiring

In summary:

• The U.S. military and the FAA have reached different conclusions about aromatic polyimide and other wiring insulation. The FAA's response certainly raises questions as to whether the FAA is exhibiting enough caution for airline passengers or putting them at undue risk.
  
  
• Visual inspections of aircraft wiring are inadequate to detect cracks.
  
  
• The nation's aircraft are aging and many are flying in excess of 100,000 hours, which could lead to more and more wiring problems.
  

POGO recommends that the FAA needs to:

• Test and certify wiring for use in commercial aircraft.
  
  
• Require airlines to perform comprehensive intrusive inspections of the existing wiring on their planes.
  
  
• Categorize the nation's commercial fleet by wire type and age, and examine the testing that has been done on the fleet to date.
  
  
• Develop accurate service lives for wiring.
  
  
• Communicate more regularly and effectively with its military and foreign counterparts to learn of their responses to defective wiring.