FAA, an agency located within DOT is responsible for regulating and promoting the safety of civil aviation. The Coast Guard is part of DOT, except when operating as a service in the Navy during time of declared war or when the president otherwise directs; however, the Coast Guard follows its own rules for aviation safety oversight, which parallel the structure and operations followed by the military services rather than those of FAA. In contrast to FAA, DOD is both an operator and a regulator of aviation for the military services. Its primary mission is national defense, one component of which is aviation safety. OSD maintains oversight of the military services’ aircraft aviation safety processes but has delegated to the heads of the military departments the responsibility for aviation safety programs. For example, the secretary’s office is responsible for issuing policies and directives pertaining to aviation safety that the military services must implement as they address their respective missions. Within OSD, aviation safety is the responsibility of the Office of Safety and Occupational Health, under the Office of the Deputy Undersecretary for Installations and Environment, which, among other responsibilities, includes traffic safety, OSHA compliance, and toxic hazards. There are three key similarities and three differences between the aviation safety oversight systems used by FAA and the military services. They share common internal processes for disseminating safety information; managing aviation safety risks (e.g., they each use variations of a five-step process); and certifying that aircraft meet civil aviation standards (FAA provides the certification services to the military at no cost). They differ, however, in their processes to certify that aircraft meet their unique safety standards and to investigate aircraft accidents, as well as in the timetables and thresholds for acting on potential and identified aviation safety problems. For example, the command and control structure of the military services allows immediate action to be ordered, such as the grounding of a fleet of aircraft, after weighing the impact on their respective missions. In contrast, although FAA can and has taken similar immediate action when necessary, the agency often has more to consider before taking equivalent action, such as consulting with airlines and other stakeholders, given the potential ramifications for the nation’s economy and the public interest. See appendix III for additional information on key similarities and differences between FAA’s and the military services’ aviation safety oversight systems. Flight operations for military aircraft can differ from those of civil aircraft in their nature and severity (e.g., turns may be made at steeper angles and aircraft may ascend and descend at higher speeds). Although standard parts may be common, the stress on the parts and materials in the environment in which they are used may be quite different. As such, the Coast Guard and the Navy frequently fly aircraft in close proximity to water,a condition that poses special maintenance concerns, while most commercial civil aircraft are not typically exposed to similar conditions. In addition, according to some military officials, military aircraft can be operated closer to the “edge of the envelope”—maximum recommended speeds, weight, and other parameters—than commercial civil aircraft. Such conditions can also accelerate wear of aircraft. FAA and the military services oversee the safety of some similar aircraft types, such as the Boeing 737 and executive jet aircraft. See appendix II for a more detailed listing. Even dissimilar civil and military aircraft often have common parts and materials such as bolts, fasteners, and wiring. Civil and military aircraft are manufactured, modified, and repaired using standard type parts, although their application may differ. Interdepartmental communication about aviation safety issues of mutual interest is important to (1) ensure timely correction of structural, mechanical, or material weaknesses on aircraft that could lead to safety problems (e.g., loss of lives and aircraft) and (2) make effective use of federal dollars by sharing lessons learned about specific problems. Similar aviation safety concerns do not necessarily lead FAA and the military services to take the same actions to mitigate or eliminate them or to act at the same pace. Different actions taken by these entities based on assessments of safety risk can in some cases be appropriate and reflect mission differences or, in other cases, may not seem warranted. The examples below, describing the potential safety concerns associated with the choice of electrical wire insulation and the pace of equipping aircraft with warning devices to alert pilots to impending collisions, illustrates this point. Given different operating environments, the same safety risk can vary in probability and/or severity. For example, one of the military services could determine that, based on its mission requirements and a unique and harsh operating environment, an aviation safety hazard poses an extremely high risk because it is likely to occur frequently and have a critical or catastrophic impact. Conversely, FAA might determine that, based on the standard operating environment for civil aviation, the hazard poses a low safety risk because it is unlikely to occur, even if its severity is deemed critical. Given the prohibitively high cost of eliminating all potential aviation safety hazards, officials responsible for aviation safety must often accept some level of residual risk. FAA and military service officials acknowledged that some of the components used in preparing such safety risk estimates are subjective, but said they rely to the extent practical on technical experts to inform the decision-making process. When faced with a similar potential safety concern posed by the use of a specific type of wire insulation known as aromatic polyimide, FAA and each of the military services used common research findings, evidence collected from flight operations, and mission priorities to independently assess the safety risk of continued use of this wire insulation. Each arrived at different decisions about the level of hazard it posed and the actions warranted based largely upon mission differences and specific design requirements. Aviation safety officials involved in these risk assessments provided some explanations for the differing results. Environment: One of the main considerations used to assess its safety risk was the operating environment of the aircraft. For example, FAA also considered that naval aircraft routinely operate in more harsh environments than commercial aircraft–on aircraft carriers where they are constantly exposed to moisture. Ballistic Testing: To explain differences between FAA’s decision and the Navy’s decision, some officials pointed out that the genesis of the Navy’s concerns grew out of ballistic testing– a survivability issue that was not a concern for FAA and commercial operators. For example, in 1986, Navy tests found that bullets fired into an aircraft could sever wires, cause arc tracking events, and trip circuit breakers. Aircraft Design Dictates Wire Installation Practices: According to FAA and military safety officials, another consideration that guided FAA to a different result from the Navy is that transport passenger aircraft have much more room to run wires than fighter aircraft. As a result, wires require much less bending that can potentially cause their insulation to degrade. The Navy took the lead in identifying and examining potential problems associated with the use of this wire insulation type and in mitigating hazards. In the mid-1980s, when the Navy began experiencing problems with this wire insulation, it enlisted the support of experts from other military services and FAA to further characterize the problems and identify possible solutions. Researchers determined that prolonged exposure of this type of wire insulation to moisture could cause it to deteriorate and that it was susceptible to arc tracking. Arc tracking can occur when two cracks in the insulation are close enough together to allow the current to form a conductive path between them at 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. Ultimately, the Navy and the Coast Guard took the most active measures to address potential problems with aromatic polyimide, which some experts attribute to these entities’ unique aircraft operations near water. In December 1985, the Navy decided that aromatic polyimide would no longer be its wiring insulator of choice and subsequently removed it selectively from parts of aircraft where it was most problematic (e.g., fore and aft flaps, wheel wells, and around unsecured seals that could leak). The Coast Guard lagged behind the Navy in taking action to address problems with this wire insulation; however, it took the most extensive action by stripping it from its largest fleet of helicopters as a precautionary measure after occurrences of in-flight fires and cockpit smoke and fumes between 1993 and 1996. While no aircraft were destroyed, these incidents led to poor visibility in the cockpit and, in some cases, the loss of all electrically powered flight instruments. A senior Coast Guard safety official said that the Coast Guard completed removal of this wire insulation from its entire fleet of H-65 helicopters in September 2001. In contrast, the Army did not experience similar safety problems. While it independently confirmed the Navy’s findings in 1986, the Army concluded that it did not have the same problems with aromatic polyimide. The Army did have durability concerns, however; it found the degree to which aromatic polyimide chafes in Apache and Blackhawk helicopters is unacceptable over time and decided to remove it gradually as it refurbished older aircraft. In response to the Navy’s finding of potential hazards with the use of aromatic polyimide, FAA conducted independent research, tracked related research and operational data from industry and the military services, and decided that mandating the removal of this wire insulation from commercial aircraft was not warranted. However, FAA did issue three Advisory Circulars related to the use of this wire insulation type, in 1987, 1991, and 1998, to provide policy guidance to help prevent electrical problems and potential fires and to describe acceptable practices for aircraft inspection and repair, including wire installation. Recognizing the need for sustained attention to aircraft wiring issues, FAA has ongoing efforts to assess the health of wire in aging aircraft through its Aging Transport Systems Rulemaking Advisory Committee (ATSRAC). To date, working groups under ATSRAC have conducted visual (nonintrusive) and extensive physical (intrusive) inspections of wiring on aging aircraft.