The Federal Aviation Administration (FAA) issued a proposed policy statement, PS-ANM-25.853-01, for the purpose of providing guidance on acceptable methods of compliance (MOC) for the flammability requirements of Title 14 Code of Federal Regulations Part 25 for commonly constructed parts, construction details, and materials. The proposed policy statement divides materials and design features into two categories.

• Methods that are acceptable and can be used are as shown in Part 1 of the policy statement.
• Methods that are expected to be acceptable but require test data to support them are as shown in Part 2 of the policystatement.

Industry created the Flammability Standardization Task Group (FSTG) as an ad hoc action under the International Aircraft Materials Fire Test Working Group (IAMFTWG). The FSTG then initiated a 2-year substantiation activity to validate the contents of the policy in support of the FAA issuing a final policy in 2012. In September 2009, the FSTG organized a subteam to investigate the parts of the policy. Approximately 200 people were involved with this effort to standardize and simplify flammability compliance across industry. Many companies supplied data, materials, and testing.

The FSTG developed a process for substantiating each item in the policy memo. Test plans were developed and approved by industry and then made available to the FAA for concurrence. The test plan was then executed (occasionally with changes) and the data were gathered. The data were analyzed and a final report was posted for industry concurrence, followed by an FAA review. In the final report, the FSTG recommended using the MOC as written in the proposed policy; not using the proposed policy MOC; or, based on the data and analysis, using a modified approach to the MOC. The FSTG provided briefings of its activities to the IAMFTWG on a regular basis. The IAMFTWG participation is open to the public.

A series of tests was performed to determine the relative effect of test sample thickness and external ambient conditions on the flame propagation potential of carbon fiber-reinforced epoxy airplane fuselage materials. A test rig was used to simulate an inaccessible cabin area, with a fire source placed at the bottom and thermocouples positioned along the length of the test panel. The test rig could vary the ambient conditions of the external, non-fire side of the sample. A scenario of minimal heat loss was simulated by placing a 1/2-inch thick ceramic fiberboard insulation panel directly on the exterior surface, whereas a scenario of high heat loss was simulated by flowing water along the exterior surface of the panel. Different solid laminate sample thicknesses and one sandwich panel with four plies on each side of a 1-inch thick honeycomb core were tested. Post-test burn length and width measurements were made to assess the level of flame propagation. Test results indicated that the relative flammability of a composite material is dependent upon the rate of heat dissipation from the flame-impinged surface, which varies depending on the panel thickness and the heat dissipation rate at the outboard surface. Thin panels (0.04- to 0.1-inch thick) were found to propagate flames under static ambient conditions, and were also more heavily influenced by the heat transfer at the outboard surface. Thicker panels (0.13- to 0.37-inch thick) were found to have enough thermal mass between the flame-impinged surface and the outboard surface to not propagate flames under static ambient conditions, and were relatively unaffected by the heat transfer at the outboard surface. The sandwich panel was found to behave like a thin composite panel fitted with an insulated outboard surface and was entirely unaffected by the heat dissipation rate at the outboard surface.

The principles and practice of pyrolysis combustion flow calorimetry as embodied in the Federal Aviation Administration microscale combustion calorimeter (MCC) are reviewed to produce a technical basis for a standard set of operating parameters and procedures that produce accurate, repeatable, and reproducible thermal combustion properties of materials as codified in the American Society for Testing and Materials (ASTM) D7309 Standard Test Method for Determining Flammability Characteristics of Plastics and Other Solid Materials Using Microscale Combustion Calorimetry. The relationship between MCC thermal combustion properties of materials and the results of fire and flammability tests are presented and discussed.

Prototype aircraft are currently being built and tested that rely on hydrogen fuel cells to provide power for their electrical demands, and some even use hydrogen to power the entire aircraft. The problem with hydrogen is that it is extremely flammable and has never been used in this capacity before. Therefore, the flammability of hydrogen was tested from the pressure at sea level up to 40,000 feet in a 20 L vessel. The lower and upper flammability limits were found first and compared with previous data. Then, peak explosion pressure was found across all flammable hydrogen and oxygen concentrations. The oxygen concentration started from the concentration found in air and was reduced by adding nitrogen. These tests were performed up to the point where the limiting oxygen concentration was reached for each altitude. In general, as the altitude increased, the limits of flammability for hydrogen and oxygen widened, and the peak explosion pressures decreased.

This report summarizes the research work carried out on behalf of Transport Canada and the UK Civil Aviation Authority into the potential threat that might exist from contaminated thermal acoustic insulation materials). The research has been conducted in the light of related activities carried out by the industry which are also described or referenced in this report. The study is based on data analysis, literature searches, aircraft surveys, consultation with the industry, and flammability testing carried out on a test rig developed especially for this study.

This report addresses the nature of contaminants found on thermal acoustic insulation on in-service airplanes, the potential fire threat that they might present, and the actions taken by the industry to mitigate these threats. The report also makes ten recommendations aimed at improving the resistance of the airplane to hidden fires that might be fueled by contaminants.