The advisory circular "FAA AC 25.856-1 Thermal/acoustic insulation flame spread test method" published by the Federal Aviation Administration (FAA) describes a test method used to determine the flammability and flame spread properties of thermal/acoustic insulation materials. This test method is applicable to aircraft required to comply with the Code of Federal Regulations (14 CFR) Part 25, Appendix F, Chapter VI.
The guidance provided in this advisory circular is intended for aircraft manufacturers, regulatory agencies, foreign regulatory authorities, and Federal Aviation Administration (FAA) transport aircraft type certification engineers and their designees.
This advisory is not mandatory or regulatory in nature and does not constitute a regulation. It describes acceptable means to demonstrate compliance with applicable regulations, but it is not the only means. The FAA will consider other methods of demonstrating compliance that may be selected. While these guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with applicable regulations. However, if there are circumstances in which it is clear that following this advisory will not result in compliance with applicable regulations, adherence to the terms of this advisory is not mandatory and additional evidence or design changes may be requested as a basis for compliance.
This advisory circular does not change, supplement, authorise changes or permit deviations from regulatory requirements.
There is an important distinction between the flame spread assessed by this requirement and the burn length measured in the tests described in Part I of Annex F. Radiant panel testing aims to measure the actual spread of a flame through the test specimen and should be observed as it occurs during a test. Burn length, on the other hand, can usually be determined by examining a test specimen after a test has been performed. Burn length includes charring and consumption of the material, whether or not flame is evident. Flame spread is strictly an assessment of flame spread from the point of application of the ignition source. The purpose of the rule is to limit thermal/acoustic insulation to materials that do not spread fire. Since the zero spread requirement is impractical to implement, reasonable pass/fail criteria have been established to meet this purpose.
As with any rigorous test method, there may be materials that have slightly increased spreading properties that do not meet the requirement. In some cases, this may be due to an improperly constructed test specimen or a change in test procedure. To allow for such an anomaly, an acceptable method of handling the spreading length failure if one of three specimens fails is as follows. A minimum of 7 additional specimens may be tested to reach the pass criterion. None of these additional specimens will fail both criteria. In addition, the average of all specimens, including the initially failed specimen, must meet the pass/fail criterion.
For the after flame time alone, it is possible that certain materials with good propagation protection properties may exhibit modest after flame times beyond the 3 second limit. There are two ways this can be addressed to determine if the material is acceptable:
Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, it also provides testing services defined in the “FAA AC 25.856-1 Thermal / acoustic insulation flame spread test method” advisory circular with its trained and expert staff and advanced technological equipment.
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