The FAA, Transport Canada, and the UK CAA jointly developed a Risk and Benefit Cost Model to assess the likely number of U.S.-registered freighter fire accidents, and the Benefit Cost Ratio associated with seven mitigation strategies identified by the FAA. This report is structured to explain the data used by the Model Version 5, its algorithms, and the way in which the model may be used.

Model Version 5 is a development of earlier models. Extra functionality has been added and data are now appropriate to the U.S.-registered freighter fleet in 2011.

The model addresses the potential fire threat from all forms of cargo, including that from the bulk shipment of lithium batteries (primary and secondary) since it is considered they are likely to have had a contribution to two of the five freighter fire accidents that have occurred on U.S.-registered airplanes. The model displays the number of accidents through to 2021, and costs, benefits and the benefit cost ratios through to 2026.

The model predicts that the average number of total accidents likely to occur during the next 10 years, 2012 to 2021, if no mitigation action is taken, is approximately 6, ranging from 2 to 12, at 95% percent confidence interval. If no mitigation action is taken, accident costs are likely to average approximately $50 million (U.S.) per annum over the period 2012 to 2026. The primary contribution to freighter fire accident costs is the value of the airplane - with values of approximately 90% of the total accident cost for the larger freighter airplanes. However, the model predictions of accident costs are based on the assumption that the composition of the U.S.-registered freighter fleet will be largely unchanged from 2011 through 2026 in terms of the size and value of airplanes.

The costs of implementing the proposed mitigation strategies are currently not known to a sufficient level of accuracy to make accurate determinations of benefit cost ratios. However, the model has been constructed to allow user inputs of costs once they become available.

Click here to download the model (MS Excel 2007 or later, 140 MB)

A quantitative understanding of the processes that take place inside a burning material is critical for predicting the ignition and growth of fires. To improve this understanding and enable predictive modeling, a numerical pyrolysis solver called ThermaKin was developed. This solver computes the transient rate of gaseous fuel production from fundamental physical and chemical properties of constituents of a pyrolyzing solid. It was successfully applied to the combustion simulation of a broad range of materials. One limitation of ThermaKin was that it could handle only one-dimensional burning problems. As a consequence, flame spread, which is an important contributor to fire growth, could not be simulated. This technical note presents a new computational tool, ThermaKin2D, that expands the ThermaKin model to two dimensions and combines it with a flexible analytical representation of a surface flame. It is expected that this tool will enable highly accurate simulations of flame-spread dynamics. This technical note contains a description of this new computation tool, reports results of a series of verification exercises, and demonstrates some of the ThermaKin2D capabilities.

This report summarizes the research undertaken by the Federal Aviation Administration to investigate the flammability of magnesium alloys under various laboratory- and full-scale aircraft fire test conditions. During the initial investigation, a laboratory-scale test apparatus was constructed to allow flame exposure to various magnesium alloy bars as they were suspended over a small steel pan. An oil-fired burner, configured in accordance with Title 14 Code of Federal Regulations Part 25.853 (c) Appendix F Part II, was used to simulate a jet fuel fire. A variety of magnesium alloy combinations were evaluated, including two prototype alloys containing rare earth elements, when subjected to the burner flame for various durations. In most cases, the alloys melted, depositing pieces of molten material into the catch pan below. Subsequent to the melting event, the materials typically ignited, emitting an intense light during ignition. The flame duration and the amount of material consumed were measured during each test. From the initial tests, it was determined that several rare earth-containing alloys showed greater flammability resistance compared to traditional magnesium alloys, such as AZ-31. Two prototype alloy materials, WE-43 and Elektron 21, self-extinguished shortly after removing the fire source. By comparison, the AZ-31 magnesium alloy configurations did not self-extinguish and continued to burn, sometimes until completely consumed.

Additional tests were conducted to determine the ability of aircraft cabin hand-held fire extinguishers to extinguish the magnesium alloys following ignition. Halon 1211, DuPont™ FE-36™, and water extinguishers were evaluated against several different magnesium alloy fires. The Halon 1211 and FE-36 were ineffective at extinguishing the burning alloy, whereas the water was somewhat effective.

Full-scale tests simulating a survivable postcrash aircraft fire were conducted with a large external fuel fire to determine if an increased hazard resulted with seat frames constructed of magnesium alloy in the primary components. The primary components included the legs, cross tubes, and spreaders. An initial full-scale baseline test was conducted using B/E Aerospace 990 aircraft seats constructed of standard aluminum components. Follow-on tests using B/E 990 seats outfitted with components constructed from both a well-performing magnesium alloy and a poor-performing alloy were conducted to determine any increase in hazard resulting from the use of these materials in the seat frames. The tests indicated no additional hazard resulted for a majority of the test duration when using either of the magnesium alloys. However, portions of two seats constructed of AZ-31 alloy caught fire and were difficult to extinguish following extinguishment of the external fuel fire.

The ultimate goal is to use the results to develop an appropriate laboratory-scale flammability test for structural components used in the aircraft cabin, particularly the seat frames, made of potentially combustible metallic structure or composite materials.

The microscale combustion calorimeter (MCC) was developed by researchers at the Federal Aviation Administration (FAA) as a tool to evaluate research quantities of new materials. The MCC was licensed by the FAA for manufacture. Since then, many have been made and sold around the world. The FAA performed an interlaboratory study under the guidance of the American Society for Testing and Materials (ASTM) to evaluate the precision and bias of the MCC test method, ASTM D7309. This study encompassed MCCs made by several vendors and run by operators in different laboratories. Identical sets of five polymeric materials were sent to the laboratories for evaluation in the MCC. The laboratories were asked to test the samples in triplicate and report the values obtained for heat release capacity, peak heat release rate, total heat release, peak heat release temperature, and residual mass. Over 20 laboratories were asked to participate in the study. Twelve of these laboratories were able to provide data. Statistical analysis was performed on the results from the different laboratories for comparison to each other. The repeatability and reproducibility of the equipment and method were examined. Additional tests were run in the fire science laboratory at the FAA using thermogravimetric analysis to calculate the properties that are measured in the MCC. These tests were used to validate the results obtained by MCC using an alternate technique. Results from the study were very good compared to other fire tests, with a repeatability of <1% to 3.8% and a reproducibility of 2.2% to 7.9%. Recommendations for modifying the MCC methodologies were formulated and are discussed in this report to improve the results for future studies.

In an effort to minimize uncertainties seen in bench scale tests, the sources of variability in fire test data were investigated. An earlier study―a PhD thesis written by Patel at the University of Central Lancaster, UK, in 2011 titled “Investigation of Fire Behavior of PEEK-based Polymers and Compounds”―on poly(arly ether ether ketone) (PEEK) showed that the fire performance parameters of this thermoplastic changed noticeably when exposed to moisture prior to the test. The present research is a follow-up study where a series of cone calorimetry tests were conducted on conditioned PEEK specimens to analyze the previously reported ignition time scatter and its relation to surface bubble formation. Pyrolysis modeling is, subsequently, carried out to relate the moisture content with the model parameters and to explain the possible physical mechanisms that cause the difference in ignition times between wet and dry samples.