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Federal Aviation Administration Fire-Safety Mission Thomas E. McSweeny* Aircraft fire safety has always been an issue of high priority with the flying public. As the agency with prime responsibility for aviation safety, the Federal Aviation Administration (FAA) continuously endeavors to maintain and enhance fire safety. These attempts include ensuring the safety of new aircraft designs through the certification process, of new aircraft in production through manufacturing inspection, and of aircraft in use through strict maintenance and inspection requirements. All attempts involve enforcement of standing safety requirements as laid down in the Federal Aviation Regulations and elaborated upon in a variety of documents, such as Aerospace Recommended Practices, Advisory Circulars, and technical reports. These requirements are kept technologically current by dozens of ad hoc committees operating under the aegis of organizations like the Society of Automotive Engineers. in addition to the standing regulatory requirements, new standards for aircraft fire safety are periodically imposed. In the case of an immediate and known threat to safety, FAA certification authorities issue Airworthiness Directives. These require modification of specific aircraft models that have a feature identified as a safety threat. Occasionally, aircraft accidents or tests allow the FAA to pinpoint an area where a new fire safety requirement could offer demonstrable safety improvements for all aircraft of a given size or class. Such new requirements are established through a formal public rule-making process. FAA fire-safety research and development, as well as test and evaluation, have traditionally been directed to support the rule-making process for near-term attainable improvements. Such work has also served to screen out unproductive or counterproductive regulatory endeavors whose deficiencies are identified in full-scale testing. At the present time, major near-term f~re-safety research and development efforts are aimed at Malone replacement, fuselage burnthrough resistance, onboard cabin water-spray systems, cargo compartment protection, and flight data recorder fire resistance. These near-term activities have resulted in the technical basis for many fire-safety design considerations. The FAA's role in air transport safety has been fundamentally mollified through the provisions of the Aviation Safety and Research Act of 1988. This legislation has charged the FAA with the new mandate of carrying out long-term, basic research in many areas. These include not only improvement of fire safety but also how to deal with the safety of operating aging aircraft; how to understand human factors issues involving flight crews, aircraft mechanics, and air traffic controllers; and how to develop an air traffic control system to handle future fleet growth safely. Such long-range research offers the FAA a new dimension to our responsibilities of promoting a safe aviation system. It presents the FAA with organizational challenges such as obtaining resources, identifying the most productive research directions, and integrating this work into the FAA safety processes. In the specific area of fire safely, which is the subject of this conference, the FAA has developed a plan or framework for initiatives with a longer-term safety payoff. A successful *Director, Aircraft Certification Service, Federal Aviation Administration, Washington, D.C. 3
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4 Improved Fire- arm Smoke-Resistant Materials long-term fire research program will provide the FAA with the third leg of a platform to provide a stable basis for future f~re-safe aircraft. Rulemaking and Airworthiness Directives have proven their worth in the fire-safety record of today's aircraft. The flying public demands that tomorrow's record be even better, and the FAA hopes that the results of this f~re-safety research effort will provide quantum improvements over today's technology. This research framework includes six major research thrust areas. They are I. fire modeling; 2. vulnerability analysis; 3. fire-resistant materials; 4. improved systems; 5. advanced suppression; and 6. fuel safety. These areas were identified through consultations with technical experts throughout the country and together represent the FAA's view of the best comprehensive approach that could be followed with unconstrained resources. Of these fire-safety research areas, fire-resistant materials is the topic on which the Congress has placed its greatest emphasis, and coincidentally it is the one area of the six that was rated highest in priority by FAA certification personnel. Consequently, this is the first area for which the FAA has sought full funding. The quest for cabin interior materials that are more fire resistant poses considerable challenges. In only a very superficial sense can an aircraft cabin interior be compared with other ~ .~ ~ it, ~ . . . . . . . inhabited structures. While the major function of a building structure is for self-support, aircraft fuselage structural toads are dominated by the pressure differential between the interior and the low pressures found at high altitudes. Whereas building insulation is rated for its characteristics of thermal protection, aircraft insulation has a primary sound-absorbing function. This list of unique selection criteria can go on, but the importance of low weight for all elements making up the aircraft cabin interior can never be underestimated. it is for this reason that new fabrics had to be developed to provide means to fire-block aircraft passenger seats to satisfy new fire- safely standards. In a modern jet transport, the sidewall panels, partitions, ceiling, and stowage bins are typically honeycomb composite assemblies with Nomex~ core, phenolic-impregnated fabric facesheets, and decorative layers of inks and thermoplastics. Seat covers are typically wool/nylon blends, while the fire-blocking layer may be polybenzimidazole, or a blend of loomed and Kevla~9. Seat back trays are typically molded polycarbonate. Overhead passenger service units can be of metal or Declare construction. Windows are stretched acrylic, while carpets are woo! or nylon. Floor panels might be of honeycomb construction with a Nomex~ core and epoxy- impregnated graphite facings. The insulation behind the interior panels is fiberglass bagged in MylaI49 liners. Cargo liners might be polyester or epoxy-impregnated fiberglass. Graphite fabrics are gradually moving in as lighter-weight replacements for fiberglass within the cabin. Polymers play a major role in the construction of aircraft interiors due to their many remarkable properties, which allow for a variety of desired end properties, ranging from weight and durability to comfort and aesthetics.
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Thomas E. McSweeny 5 A number of fire-safety considerations are involved with airplane design, certification, and operation. Engines, as well as auxiliary power units, include fire-detection and extinguishing systems. Wing fuel vents have flashback arrestors to minimize lightning hazards. Designated engine firewalls acne flammable fluid-hose assembly designs must pass specified fire-endurance tests. Ducts carrying heated air from engine compressors have associated hot-air leak detectors for hot-air lakes. The routing of flammable fluid lines avoids areas having potential ignition sources. Main landing gear wheels are braked to a stop after lift-off to prevent damage to hydraulic systems from thrown tire belts. Landing gear tires are pressurized with nitrogen to prevent auto-ignition of tire pyrolyzate resulting from overheated brake mechanisms. Wiring within the airplane pressure vessel employs low-flammabiliyv insulation like Kanton@. Circuit breakers further protect the wiAng from overheat. -her The basic philosophy for fire safety in materials design and selection involves one or more of four goals depending on the fire threat and required functional performance of the material. These goals are 1. 2. 3. 4. low ignitability; low heat release; fire containment; and fire endurance. Low ignitability, as demonstrated by a modified Bunsen burner test, is a requirement for most aircraft interior materials. Seats, as well as cabin interior panels, must demonstrate low heat release in addition to the ignitability requirement. Seat cushions configured in a mock-up assembly are allowed a specified weight loss when exposed to direct flames from a 2-gallon-per- hour of! burner. Panels are limited in both peak and total allowable heat release as tester! in the Ohio State University Rate of Heat Release Apparatus. A fire containment requirement is imposed on cargo liner materials. The liners are expected to prevent cargo compartment fires from spreading beyond the confines of the compartment. For small compartments, fire control is achieved through oxygen starvation. In larger compartments, a detection and suppression system is deployed. In the former case, cargo liner integrity is needed to keep fresh air out of the compartment. In the latter case, the liner integrity is needed to keep in both the fire and the extinguishing agent. The test requirement for cargo liners also involves the use of a 2-gallon-per-hour burner. Fire containment clearly includes fire endurance as a necessary requirement. Fire endurance is the goal of fire-safety requirements for emergency escape slides. The fire test involves exposing slide fabric, stretched by pressurization, to a radiant source. The endurance of slide material to the radiant heat from a fuel fire is enhanced when the slide fabric has an aluminized coating. Additional aircraft cabin fire-safety features include lavatory smoke detectors and trash- bin extinguisher bottles, mandatory hand-held extinguishers for onboard use, floor proximity escape path lighting, and protective breathing equipment for the cabin and flight deck crew. Aircraft fire safely is a complex issue. Quantum safety improvements will require a joint effort between the FAA, the air transportation industry, and other interested and affected parties. To be successful in this effort, we in the FAA need your help to meet these new challenges.
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6 Improved Fire- arm Smoke-Resistant Materials This conference hosted by the National Materials Advisory Board is a beginning to get your input, and ~ am confident that the conference will be productive.