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Good morning, Madame Chairwoman and members of the Committee. I am pleased to represent the National Transportation Safety Board (NTSB) before you today regarding aircraft electrical wiring issues.

Electrical systems are critical to the safe operation of transport category airplanes, and wiring is used to distribute power and communication signals throughout these systems. Many transport category airplanes contain over 100 miles of wiring. Today, I would like to discuss the Safety Board's efforts to address aircraft wiring issues raised in accident and incident investigations, including the recent investigations of TWA flight 800, and the Canadian investigation involving Swissair flight 111.

As background, let me begin by describing how electrical wiring is constructed, routed through airplanes, and how the malfunctions can occur. Electrical wire consists of a conductor that is encased in a protective layer of insulation. Wire is routed throughout an airplane in a series of bundles with clamps and connectors. Safe routing practices include measures to prevent wires from wear, abrasion, contamination, and contact with other components; to gently bend and turn wires during installation to prevent cracking of the insulation; and to physically separate wires from systems whose signals may interfere with one another. Guidelines for these safe wire routing practices in aircraft are described in a series of Federal Aviation Administration (FAA) advisory circulars and manufacturer standard practices manuals.

When the protective layer of insulation on a wire is compromised and the conductor is exposed, the potential exists for a hazardous electrical system malfunction caused by a short circuit or an arc. A short circuit occurs when electricity takes an unintended path. For example, condensation and other conductive materials that are sometimes found on wire bundles can bridge the gap between a wire conductor and adjacent metallic structure. When electrical current follows the unintended path to the metallic structure, a short circuit that could interrupt the function of an electrical system occurs. Short circuits can transfer power to adjacent wires or draw an excessive current from the power source, overheating wires and creating fire hazards. Electrical arcing is a type of short circuit in which high current crosses a gap, emitting sparks. The sparks include molten material from the wire conductor as it is vaporized by the high energy discharge, producing extremely localized heat. The arcing could ignite flammable products in the area and could potentially initiate an explosion. Obviously, safeguards must be maintained to preclude arcing, particularly in the vicinity of flammable materials or explosive fuel-air mixtures.

Since 1983, the Safety Board has investigated 15 transport category airplane accidents or incidents that involved electrical wiring malfunctions. As a result of those investigations, we have issued 34 safety recommendations regarding electrical wiring malfunctions. I would like to summarize some of the accidents and the recommendations that resulted from them.

In May 1984, the crew of a McDonnell Douglas DC-10, operated by Northwest Orient Airlines, observed smoke and sparks in the cockpit after takeoff from Minneapolis, Minnesota. An emergency was declared and the airplane returned to Minneapolis and landed safely. The Board's investigation revealed that a wire bundle behind the instrument panel was improperly routed and contacted a metal bracket, causing several wires to short circuit and arc. It could not be determined if the bundle was misrouted during manufacture or subsequent maintenance, but the Safety Board issued an urgent recommendation for an immediate inspection of this wiring in all DC-10s. The FAA complied and, in July 1984, issued an airworthiness directive mandating an inspection of all DC-10s to ensure that the wiring was not chafed and was routed properly in this area.

In May 1990, a Boeing 737 operated by Philippine Air Lines exploded and burned on the ramp in Manila, Republic of the Philippines. Of the 119 persons on board, 8 were fatally injured. The investigation, conducted by the Philippine government with participation from the Safety Board, revealed that an ignition of a fuel-air mixture in the center fuel tank was the cause of the explosion and subsequent fire. A portion of the wiring that led to the center fuel tank float switch was found with the insulation compromised and the conductor exposed. The Safety Board issued an urgent recommendation to the FAA in August 1990 requesting an immediate inspection of the float switch wiring of all similar Boeing 737s. Unfortunately, the FAA, in May 1991, informed the Board that it did not believe this wiring failure contributed to the accident and did not plan to mandate an inspection. The Safety Board classified the recommendation "Closed - Unacceptable Action."

In March 1991, a Lockheed L-1011, operated by Delta Air Lines, experienced a fire in the passenger cabin while en route from Frankfurt, Germany, to Atlanta, Georgia, with 231 people on board. A flight attendant saw flames coming through the cabin floor near a row of passenger seats and discharged a fire extinguisher. The flightcrew declared an emergency and landed safely at Goose Bay, Canada.

The investigation, conducted by the Transportation Safety Board of Canada (TSB) with participation from the NTSB, revealed that the fire originated near a wire bundle routed below the cabin floor that had been routed with an extremely tight bend, which can crack wiring insulation. Some of the wires in this bundle showed evidence of electrical arcing. Nearby metallic debris found in the area included nail clippers and loose screws. Adjacent portions of the wire bundle were covered with a blanket of flammable lint and dust more than two inches high; some of this lint appears to have fed the fire. In August 1991, the Safety Board recommended that the FAA require specific inspections of wire bundles on transport category airplanes to ensure proper routing and the removal of flammable lint and dust accumulations. In October 1991, the FAA determined that the approved inspection criteria regarding wire bundle installations for Boeing and McDonnell Douglas aircraft were adequate. However, the FAA issued a handbook bulletin to principal maintenance inspectors to review their operators maintenance programs to ensure that they included inspection of aircraft wiring. Although in October 1992, the Safety Board classified the recommendation as "Closed - Acceptable Action," the results of other investigations that will be discussed later indicate that the FAA's actions did not effectively address the issue of removing contamination from wire bundles.

In April 1997, a Cessna 650 Citation operated as a corporate flight, caught fire while on approach to Buffalo, New York. While descending through 4,000 feet, the crew smelled smoke, then lost all radio communications. After landing, ground personnel saw flames burning through the fuselage. The flightcrew and passenger exited safely, but the airplane was substantially damaged. The Safety Board's investigation revealed that the fire started when contact between electrical wiring and a hydraulic line caused the ignition of hydraulic fluid. FAA guidelines state that under no circumstances should electrical wiring be routed within ½ inch of a hydraulic line, and any wiring routed within two inches of a hydraulic line should have clamps installed to ensure positive separation. However, design drawings for the Cessna 650 specified ½ inch of clearance and did not require clamps to ensure separation. Following the Safety Board's findings, the FAA issued an airworthiness directive in May 1997, to mandate the installation of clamps to ensure positive separation.

During the course of the Cessna Citation investigation, the Safety Board learned of three Boeing 767 events in which safety hazards were created because wiring was not routed with appropriate clearance from adjacent components. In two of the events, flight control cables failed when they rubbed against electrical wiring resulting in arcing, and in the other case, a cockpit fire hazard was created when electrical wiring arced to an oxygen line in the cockpit. Based on the Cessna 650 accident and the Boeing 767 events, in January 1998, the Safety Board issued recommendations requesting that the FAA review the design, manufacturing, and inspection procedures of all aircraft manufacturers to ensure that adequate clearance, in accordance with published FAA guidelines, is specified around all electrical wiring.

Although a March 1998 response indicated FAA agreement with the intent of these recommendations, a June 1999 letter indicated that FAA found that manufacturers were in compliance with the intent of the published guidelines. This response was not consistent with the Safety Board's findings as detailed in the recommendation letter and the recommendations are currently in an "Open" classification.

Two recent major accidents have further focused the Safety Board's attention on aircraft wiring - TWA flight 800 off Long Island, and Swissair flight 111 off Nova Scotia. Let me begin with a discussion of Swissair flight 111.

On September 2, 1998, a McDonnell Douglas MD-11, operated by Swissair as flight 111, crashed into the Atlantic Ocean near Peggy's Cove in Nova Scotia, Canada. All 229 people on board were killed. About one hour after takeoff from New York, the flightcrew notified air traffic control of smoke in the cockpit, requested to divert, and was cleared to Halifax International Airport. About 11 minutes later, the flightcrew detected multiple airplane electrical system malfunctions. The flightcrew declared an emergency, but all communications between air traffic control and the flightcrew ceased shortly thereafter. Approximately 6 minutes later, the airplane crashed.

The TSB is in charge of the accident investigation, and the NTSB is participating in accordance with the provisions of Annex 13 to the Convention on International Civil Aviation. Approximately 90 percent of the airplane's wreckage has been recovered from the Atlantic Ocean. Examination of that wreckage revealed fire- and arc-damaged wires in the ceiling of the cockpit and forward cabin area. Investigators found evidence of electrical arcing on several wires near the cockpit overhead circuit breaker panel. Some of the damaged wires in the forward cabin ceiling were associated with the in-flight entertainment system and, as a precautionary measure, the system has been disabled in all Swissair MD-11s and Boeing 747s, the only airplanes with that particular entertainment system.

The investigation is still underway and the TSB has not determined if electrical arcing was the cause of the fire. However, on January 11, 1999, in coordination with the TSB, the Safety Board issued a recommendation to the FAA for an inspection of the wires in the vicinity of the cockpit overhead circuit breaker panel of all MD-11 airplanes. One month later, the FAA mandated that all operators perform such an inspection; a fleetwide inspection of all wiring in the ceiling of the cockpit and forward cabin was subsequently performed by all operators. Discrepancies found were reportedly not considered significant by the operators but included broken wire insulation, loose wires, wires improperly contacting structure, and non-conformal or damaged clamps, standoffs, wire ties, and terminal strip covers.

Let me now discuss some of the wiring issues raised during the TWA flight 800 investigation. As you know, on July 17, 1996, a Boeing 747, operated by Trans World Airlines as flight 800, crashed into the Atlantic Ocean shortly after takeoff from John F. Kennedy Airport in New York. All 230 people on board were killed. The investigation of this accident has been one of the most extensive investigative efforts in the Safety Board's history. Based on an evaluation of the recovered wreckage and a detailed study of the sequence of break-up events, we have determined that the fuel-air vapor in the center fuel tank ignited, causing an explosion of the tank, and initiating the breakup of the airplane.

To date, we have not identified the ignition source that sparked the explosion on TWA flight 800. Our search for the ignition source includes an evaluation of the airplane's wiring. The Boeing 747 has an electronic fuel quantity indicating system (FQIS) that measures the amount of fuel aboard the airplane and displays that information in the cockpit. This system includes electrical probes that are mounted in each fuel tank. As the fuel level in a tank drops, a corresponding change in the electrical properties of the probes is detected by the fuel quantity indicator. There are seven such probes in the center wing fuel tank. Wiring for the probes, which is manufactured with Teflon insulation, is designed to carry a low voltage (maximum 26 volts) and low current electrical signal needed for each fuel tank probe to operate.

Although not yet complete, the investigation has already uncovered several concerns about the FQIS wiring that the Safety Board addressed in recommendations issued to the FAA in April 1998. Investigators learned that this wiring was routed in bundles with nearly 400 other wires, some of which carry up to 350 volts. Because of concerns about the potential for a wiring malfunction that would permit excessive electrical energy to enter a fuel tank and ignite an explosive vapor, the Safety Board recommended that the FAA require the FQIS wiring to be separated from other wires to the maximum extent possible.

In September 1998, the FAA responded by issuing an airworthiness directive mandating the separation and shielding of FQIS wiring in Boeing 747s, and in February 1999, the FAA issued a similar airworthiness directive (AD) to address Boeing 737 wiring. More recently, on August 30, 1999, the FAA issued a notice of proposed rulemaking to require an inspection to detect certain discrepancies in the wiring of the FQIS on DC-9 series airplanes in the area where the wiring passes through the cargo compartment. According to the FAA, these discrepancies, which may have been caused by maintenance or alteration practices, can permit excessive electrical energy to enter the fuel tanks through the FQIS wiring and result in a potential ignition source in the fuel tanks. FAA action regarding the separation and shielding of FQIS wiring in the DC-9 and other transport aircraft is pending.

Safety Board investigators also found that a connector on certain tank probes was designed in a manner that allows its sharp edges to cut through the insulation of wiring, which could create a spark gap. As a result, the Safety Board recommended the replacement of such connectors on fuel tank probes. The FAA responded by issuing an AD (AD 99-08-02) to address this issue.

The Safety Board's investigation team has performed a detailed examination of the wires, wire bundles, and electrical connectors that were recovered from the TWA flight 800 wreckage. The team found:

• fuel tank wiring that had been repaired using string and adhesive tape - a repair technique not permitted inside fuel tanks;
• wiring with insulation cracks that exposed the conductor;
• wire bundles contaminated with semi-conductive residues; and
• metal drill shavings along the path where FQIS wiring was routed.

In an effort to determine if these findings were unique to TWA flight 800 or if they existed on other transport aircraft, the Board examined wiring on more than 20 other transport category airplanes. The examination included 13 older Boeing 747s, similar to the TWA flight 800 airplane, and Boeing 737, 757, 767, DC-9, MD-90, and A300 airplanes. The age of the airplanes surveyed ranged from new to 27 ½ years old. The examinations found:

• accumulations of contaminants on wiring that included lint, grease, liquids, paper, and metallic corrosion inhibiting compounds;
• wire bundle clamps (designed with rubber lining to protect the wiring) that cut into wiring when the rubber lining crumbled; and
• chafing and cracks in the insulation of wires, deep enough to expose the conductor.

These findings have raised the Safety Board's concern about the safety of electrical systems as airplanes age.

After participating with Safety Board investigators in the February 1998 examinations, and in response to recommendations from the White House Commission on Aviation Safety and Security, in March 1998, the FAA formed the Aging Non-Structural Systems team, which consisted of Boeing and FAA personnel. This team evaluated the condition of the wiring on five in-service transport category airplanes that were undergoing maintenance.

The team's findings, published in the July 1998 "FAA Aging Transport Non-Structural Systems Test Plan," were similar to the Safety Board's earlier findings and included examples of deterioration of wiring, connectors, and clamps, and contamination of wire bundles with metal shavings, dust, and other fluids. The team concluded that current maintenance practices do not adequately address wiring, and outlined seven tasks that should be taken by the FAA by 2001 to address these concerns. The tasks included: (1) establishing an oversight committee, (2) conducting an in-depth review of the aging transport fleet, (3) enhancing aging airplane systems maintenance, (4) adding aging systems tasks to the aging airplane research program, (5) improving reporting of wiring system discrepancies, (6) evaluating and addressing fuel system wiring hazards, and (7) improving wiring installation drawings and instructions for continuing airworthiness. Progress on these tasks is being monitored by the FAA Aging Transport Systems Oversight Committee.

However, the Safety Board's staff has noted in recent industry meetings and seminars that operator personnel have questioned the merit of performing wiring inspections, indicating that they have not detected significant discrepancies. This is certainly at odds with the findings from the Safety Board and FAA examinations. The Safety Board remains concerned about these issues, and we will closely monitor the progress of this effort.

The Safety Board is currently performing a series of wiring tests in conjunction with the TWA flight 800 investigation. One test is documenting the electrical short circuit and potential arcing characteristics of a wire bundle contaminated with various fluids, including water and lavatory waste. In another test, we have placed metal drill shavings on wire bundles, then vibrated the bundles to learn how the shavings cut into the insulation of the wires, and examined the power transferred to adjacent wiring if this occurs. Reports on these tests will be placed in the public docket this summer.

In another series of tests, the Safety Board will examine the concerns operators have about handling or disturbing the wiring, especially in older airplanes, during maintenance activities because of the potential to crack the insulation. The NTSB obtained wiring samples from transport airplanes -- both currently in-service and recently retired -- that have been in service for over 20 years. We are subjecting these samples to the same battery of tests that they were required to pass before installation, including insulation resistance, thermal shock, bending, and shrinkage. The results will help the Safety Board evaluate the effect of aging on electrical wiring, and will provide new insight into whether aged wiring provides an adequate level of safety compared to new wiring. We note that the FAA Aging Transport Non-Structural Systems team plans to conduct similar tests in the future. We will, of course, share the results of our tests, which we expect to be completed this summer, with the FAA, industry, and the public.

Significant attention has recently been given to a specific type of wiring with insulation made from an engineered plastic coating, sometimes referred to by the Dupont Corporation trade name Kapton, and questions have been raised about the susceptibility of this wiring to a phenomenon known as "arc tracking." Arc tracking occurs when the insulating material chars. The charred insulation is conductive, can sustain and propagate an arc along the length of the wire, and may flash-over to consume adjacent wire insulation or other combustible material. The majority of the wiring in the TWA flight 800 accident airplane was insulated with a double-layered version of an engineered plastic known by the Raychem trade name Poly-X. We are now performing tests to determine if this type of wiring is also susceptible to arc tracking. The Safety Board has not issued any recommendations regarding wire insulation composition, but future recommendations may be developed depending on the results of the tests we are conducting.

Finally, it should be noted that the primary device for protecting an aircraft from the hazards of electrical malfunctions, the circuit breaker, does not protect against arcing faults. Although circuit breakers do protect against the electrical overheating of wires, they do not protect against arcing faults because circuit breakers are designed to activate based on the heat input. Arcs develop high energy, but in a very short period of time. Safety Board staff has met with industry representatives who are developing devices known as arc-fault interrupters for potential use in aircraft. These devices can recognize the rapid current and/or voltage signatures associated with arcing faults and act to interrupt the circuit. We will continue to monitor the development of this technology and believe this technology is important to the protection of critical aircraft systems from the dangers associated with electrical arcing.

Madame Chairwoman, we appreciate the opportunity to share some of the Safety Board's experience with regard to aircraft wiring failures, and to share our concerns about wiring maintenance, particularly as airplanes age. The Safety Board is concerned that industry and regulatory efforts have been relatively ineffective in preventing the types of wiring hazards seen during the TWA flight 800 investigation. Our wire examinations have shown us that it is virtually impossible to eliminate all potential ignition sources, and underscores our belief that the flammability of fuel vapors be reduced as much as possible. Our recommendations to the FAA on this issue are still open.

Although the Board is not prepared at this time to offer additional specific recommendations, our concerns regarding aging aircraft wiring safety include: ensuring that low voltage fuel system wiring is separated from high voltage wiring from other systems; ensuring that no wiring is routed in proximity to flammable oxygen, fuel, and hydraulic lines or critical flight control cables; and preventing the contamination of wiring by fluids, flammable lint, metal shavings, or other debris.

That completes my statement, and I would be pleased to answer any questions that you may have.