Aging aircraft wiring problems and solutions - Essay Example

Running Heading: AGING AIRCRAFT WIRING Aging Aircraft Wiring Problems and Solutions Aging aircraft wiring has been a cause of significant threat to both invaluable human life and material. It is almost certain that a smart wiring alone will not be the solution to this problem considering the working conditions of an aircraft. Keeping this scenario in mind this paper is trying to consider a few of the most pressing safety problems in aviation today. Furthermore, this work will explain, as an operator, how one can think about designing a safety program element. This is going to be an equipment of skill for any operator to upgrade his/her expertise in the subprogram and process level. Introduction 'The problem of aging aircraft wiring received a great deal of attention in the late 1990s due to two tragic accidents: the July 1996 mid-air explosion of the Boeing 747 TWA Flight 800 and the crash of a Swissair MD-11 in Nova Scotia. The NTSB (National Transportation Safety Board) later determined the cause of the TWA 800 accident to have been a wiring failure that led to an ignition spark in the fuel tank. The Swissair disaster is believed to have been caused by electrical arcing originating from an in-flight entertainment cable. These disasters provided the initial impetus to begin reshaping commercial wiring policies' (Kevin R. Wheeler and Dogan A. Timucin 2007). A TWA747, flight 800, heading for Paris and Rome with 230 from JFK international airport on the night of July 17, 1996, exploded shortly after take off and during initial climb out. The huge aircraft was blown up killing all the passengers and crew aboard. One of the most extensive aircraft investigations in the history was initiated following the crash. After many findings the initial fear of a terrorist missile attack was vanished. Enormous efforts were vested on the recovery process along with the FBI and NTSB investigations. The search was supported by FAA, US Navy Boeing and hundreds of contractors. Finally, the remains of the aircraft were recovered from Atlantic. To the continuing frustration of conspiracy theorists, investigators determined that the aircraft was not downed by a bomb or missile, but rather fell victim to a much more insidious enemy - faulty wiring. Hot or chafed wire is believed to have ignited the fuel vapors in the empty center wing tank, creating a massive explosion and in-flight breakup of the aircraft. The similar incidents occurred in the aviation industry at regular intervals. Obviously the wire and connector fault detection and prognosis problem is difficult and each agency is doing the best that it can with the resources given (J.S. Barrett and M.A. Green 1994). Thus, developing the appropriate theoretical approach, using simulations and data collection for development and eventually leading to requirements definition for all aspects of the wiring fault detection problem seem to be a huge task. The terrific crashes remind us that the aircraft electrical system malfunctioning can lead to tragic eventualities in terms of human life and monetary loss. Wiring problems often lead to troubleshooting nightmares, and canceled missions. With miles of wire bundles running through barely accessible compartments, inspecting and repairing wiring problems can eat up your maintenance budget and resources in a very short time. To help maintenance managers address these types of issues, we investigated the tools and techniques that can be used to minimize down time and improve safety. Jim sparks (2004) felt that 'wiring in aircraft has been installed without much thought given to the overall life. The concept has been one of "fit and forget." Various failure modes and their severity may not have been considered during the design or modification process. Maintenance programs often did not address the impact of insulation breakdown and resulting arcing, nor was consideration given to the probability of splices developing high resistance or increasing the strain on a wire bundle. Service history also indicates that Foreign Object Damage (FOD) such as drill shavings or caustic liquids will cause wiring degradation'. Under the Wire Attacks on wiring insulation can come in many types: first of all extreme heat or cold swinging can cause either hardening or softening of the wire, humidity and chemical spills or leaks can create brittleness, mechanical strains can fatigue the wire conductor creating a gap that can arc and generate heat. Over voltage can cut holes in insulation leading to flashover. Mechanical damage that occurs during the wire installation, often in the form of metal chips lodged in wire bundles, can go undetected for years. Tight bend radiuses can chafe the insulation and also fatigue the conductor (E. Bechhoefer, J. Yu 2005). Short or open are the two simple terms by which most electrical problems could be described. An inoperative component is resulted when a wire breaks cleanly and terminates the connection. With a short circuit, the load is bypassed and the surge in current should trip the circuit breaker. The occasion becomes most dangerous when the there is a weakened insulation and current jumps out as a spark or a corona discharge. Insulation does not have to completely disappear for this to happen. The insulating properties can grow weaker with the effects of age, ozone, ultraviolet and chemical attack, resulting in increased resistance to produce heat. The heat would only need conducive conditions such as just a fuel source or and oxygen to create fire (Lo. C and Furse C 2005). It is understood that some costly improvements are deemed worthwhile. Others are not. And sometimes, it takes an airplane crash to create sufficient pressure for the aviation industry to spend money for safety (Christine. N 2004). Polymers such as aromatic polyimide, alkene imide are the main raw materials used in the production of aircraft wire. In the late 1980s, one famous wiring insulation type that received a bad reputation was DuPont Kapton. The material has great temperature stability characteristics from extreme hot to extreme cold but is much thinner and lighter than similar materials. This light weight made it highly desirable for aircraft manufacture and its use was widespread. Like all insulators, Kapton is susceptible to degradation, but its thin shell made it susceptible to chafing and wears modes as well. 'As part of a larger effort to assess the problems associated with senior aircraft, the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) was created, and in part due to the TWA and Swissair accidents, scientists at the Aging Aircraft Laboratory at the National Institute for Aviation Research (NIAR), located at Wichita State University, conducted a comprehensive wiring assessment of two high-time commuter aircraft. Both were torn down and inspected using several non-destructive techniques such as general and intrusive visual inspections. Destructive testing was also performed to determine condition of the wiring. Circuit breakers were examined as well' (Christine. N 2004). The results of the destructive tests showed that the characteristics of wires in the aircraft were generally good, which meant that the insulation properties pretty much met wire specifications. However, the tests also highlighted several areas of concern. "The results of the inspections revealed several wire defects, resulting from aircraft use," said Dr. Steven Skinner, a professor at Wichita State's College of Engineering, who performed the assessments as part of the aging aircraft study. "The main defects were rubbing/chafing and cutting through of the wire's insulation. These were mainly due to the wires and wire bundles rubbing against some structure of the aircraft, due to improper clearance. Most of these defects could have been detected and corrected through proper maintenance but were seemingly ignored, not given the same attention as other aircraft structures." As for the circuit breakers, Skinner said, "Many of the breakers did not initially function according to their rating, but manual cycling greatly improved their performance. This suggests that circuit breakers become sticky' over time if they are not cycled and that periodic cycling of circuit breakers should be implemented as part of the maintenance routine." Of course you should always follow aircraft flight and maintenance manuals for proper operation and testing of circuit breakers, but how many times have you observed breakers that are difficult to cycle That's probably an indication of trouble (Christine. N 2004). Wire Maintenance Careful attention to the aircraft wiring is important as the wiring maintenance of the aging aircraft is critical. Ron Grose, Falcon Technical Specialist at Duncan Aviation's Lincoln, Neb., service center said that "Most of the guidance material involves creating more awareness about the importance of wiring for aircraft safety," he was an active member of an organization whose mission was to address issues involving business and corporate aircraft. Grose advises that wiring related problems take a long time to develop so it is vital to take the proper actions early to keep the problems from evolving. One needs to look for wire bundle chafing and deterioration at adel clamp rubber cushions use good shop practices and do not hang work lights on the wire bundles and be very careful when working around bundles to prevent chemicals or metal shavings from getting in the wires. Many of the manufacturers have repair instructions for wires, wire bundles and connectors. When choosing a shop to repair your aircraft, make sure they are aware of the best practices' to protect your wiring, and follow the guidance material for wiring modifications and STCs. On inspecting wire bundles, you may come across discoloration of the insulation and also a occurrence called "whiskering." insignificant holes in the insulation will draw tin from the copper alloy and grow tiny spikes probing for another conductor. Pay scrupulous concentration to uncovered wire bundles in susceptible areas like the landing gear bays, control surface actuator areas, and engine compartments that can pick up debris. Baggage takes a lot of knocking about and should be cautiously checked for harm. Be extra cautious when applying anti-chafe substance to wiring bundles and be certain to follow approved methods. Some older anti-chafe material actually causes chafing and hides the bundle from visual inspection. Non-intrusive techniques to assess wiring health. Degradation of wiring insulation, coupled with wire chafing, is a problem noted on many of our aging aircraft. This creates not only a significant maintenance burden but also a potential safety issue should flammable fluids or explosive vapors be present. Attention is beginning to be focused on developing techniques to determine the integrity of wiring system. However, we must emphasize the need to develop quick, simple, non-intrusive methods that can pinpoint low-level shorts associated with a specific wire (William C. Kinzing 2001). As an operator or technician on should have a capability to predict remaining life of components and wiring. The need does exist to establish some method to predict remaining life so that we can plan the necessary maintenance actions to improve aircraft availability and reduce maintenance cost. One potential technique for electrically driven components would be to develop a correlation between electrical signature (e.g. current draw) and component wear. Some work has been done in this area with promising results. There may also be other techniques that could be developed with similar results (Department of the Air Force 2001). New technology such as arc fault circuit interrupters are currently available for newer aircraft and will greatly improve the safety of the aircraft in which they are installed. And tiny sensors are being developed along with smart wire technology that will indicate faults and provide power status monitoring. The sad news is that most of this emerging technology will probably never make it into the thousands of existing aircraft. The miles of electrical wiring in your aircraft can hide a potential tragedy as seen on TWA 800 and Swissair 111. The apparition of these catastrophic wiring failures should add force to the message that all wiring maintenance must be addressed with the highest levels of professionalism and skill. Train one as a technician and acquire oneself the most current wire inspection, maintenance information and guidance. Until the day comes when wires tell us about their condition, it is up to the maintenance technician to diligently and skillfully inspect and maintain aircraft wiring systems, to keep one's crews, passengers and aircraft safe. It is again worth noticing that the leading wire chafing detection efforts in the United States have devoted minimal effort to simulating the best type of signal to inject even though the success of the technology development efforts depends upon understanding electromagnetic wave propagation. As technicians Understanding how the electromagnetic wave propagation changes within wiring with damaged insulation is fundamental to developing signal injection and measuring devices for fault detection and prognosis. Reference Christine. N (2004) Aging Aircraft: important work done on the FAA ARAC "Aging Aircraft" Working Group, including aging wiring. Department of the Air Force (2001) Mechanical and Subsystems Integrity Program; E. Bechhoefer, J. Yu(2005)Algorithm Development to Ascertain the True Characteristic Impedance of a Wire for Wire Diagnostics; Proceedings of the 2005 IEEE Aerospace Conference, pp.3797-3802. Jim sparks (2004) The effects of old age on wiring systems. Avionics technology. J.S. Barrett and M.A. Green (1994) A Statistical Method for Evaluating Electrical Failures", IEEE Transactions on Power Delivery, Vol. 9, No. 3, pp. 1524-1530. Kevin R. Wheeler and Dogan A. Timucin (2007) Aging Aircraft Wiring Fault Detection Survey; Wiring Fault Detection Challenge Problem Version 1.0 Lo. C. and C. Furse (2005) Noise-Domain Reflectometry for Locating Wiring Faults; IEEE Transactions on Electromagnetic Compatibility, Vol. 47, No. 1, pp. 97-104. Negaard, G.R (1980) The History of the Aircraft Structural Integrity Program; Aerospace Structures Information and Analysis Center (ASIAC), Report No. 680.1B. William C. Kinzig (2001) USAF Strategy for Aging Aircraft Subsystem Research and development: Paper presented at the RTO AVT Specialists' Meeting on "Life Management Techniques for Ageing Air Vehicles". Read More