John W. Reinhardt, David Blake, & Timothy Marker

This report documents the test results of the testing conducted during the development of a minimum performance standard for aircraft cargo compartment gaseous fire suppression systems. It also includes the final version of the standard. The development work was performed in conjunction with the International Halon Replacement Working Group.

Timothy Marker

A large number of small-, intermediate-, and full-scale flame propagation tests representative of an in-flight fire were conducted on various thermal acoustic insulation blanket materials. Results indicated that the current Federal Aviation Administration (FAA) vertical Bunsen burner test requirement could not adequately discriminate between poorly performing materials and materials that performed well under realistic fire scenarios. A radiant panel laboratory test was shown to be an effective method for evaluating the in-flight fire resistance qualities of thermal acoustic insulation.

In addition, a new laboratory test was developed for evaluating the postcrash fire burnthrough resistance of thermal acoustic insulation. The test method was based on full-scale tests in which a fuselage structure was subjected to jet fuel fires. Approximately 60 burnthrough tests were conducted on a variety of insulation materials. Insulation materials compliant with the new burnthrough test method will provide a minimum of 4 minutes of protection against a postcrash fuel fire.

Jennifer R. Stewart

Two different types of polymers were synthesized and their degradation and combustion behavior were investigated. The first class, 1,1-dichloro-2,2-(4-hydroxyphenyl)ethylidene (bisphenol C) based polymers, were found to be among the most fire-resistant polymers with peak heat release capacities as low as 20 J/g-K. Polymers containing bisphenol C all exhibited exothermic decomposition behavior. When compared to corresponding bisphenol-A-based polymers, these bisphenol-Containing polymers had higher char yields and lower decomposition temperatures. The presence of bisphenol C in materials, whether as a co-monomer or blends, showed a char enhancement effect; yielding higher char than what is expected by a purely additive effect.

Bisphenol C polyarylates and polycarbonates yielded large amounts of HCl and carbon dioxide upon decomposition. Compared with other bisphenol-based polymers, polycarbonates and polyarylates containing bisphenol C yielded significantly less amounts of monomer. Decreasing the concentration of bisphenol C in the copolymers or blends yielded' relatively more monomer in the degradation products.

The second class of polymers studied were polycarbodiimides, which generally decompose in an endothermic manner to yield quantitative amounts of monomer. The incorporation of TEMPO-containing side-chain substituents altered the degradation. TEMPO-based polycarbodiimides decomposed in an exothermic fashion and yielded several other degradation products in addition to the original monomer. These free-radical-containing polymers showed a 25% reduction in the peak heat release capacity when compared with the control polymer. Neither polymer was found to be fire resistant which is due to their high organic content and essentially 100% weight loss during decomposition.

Steven M. Summer

Experiments were conducted within a simulated aircraft center wing fuel tank (CWT) to qualitatively analyze the effects of decreased ambient temperatures, such as might occur at increased altitudes, on the vapor concentrations found in a typical CWT ullage. A small quantity of fuel in the CWT test article was heated to 125°F for two hours, corresponding to a temperature of approximately 10°F above the flashpoint of the fuel. The tests were conducted at sea level (14.7 psia), however, the wall temperature of the tank was cooled to a temperature corresponding to a given altitude.The following reallife scenarios were simulated.

1. BASELINE TEST: The environmental conditioning system (ECS) packs are run for two hours while the aircraft is on the ground. After some time, the packs are turned off, and the aircraft remains on the ground.

2. LOW-ALTITUDE TEST: The aircraft, after running its ECS packs, takes off and climbs to a low altitude, of approximately 9,000 ft, cooling the CWT to approximately 55°F.

3. INTERMEDIATE-ALTITUDE TEST: The aircraft, after running its ECS packs, takes off and climbs to an intermediate altitude of approximately 22,000 ft, cooling the CWT to 15°F.

4. HIGH-ALTITUDE TEST: The aircraft, after running its ECS packs, takes off and climbs to a full altitude of approximately 30,000 ft, cooling the CWT to -20°F.

From these tests, it was determined that the ambient temperature does indeed have a significant effect on the vapor concentrations formed in the fuel tank ullage at small fuel mass loadings. When allowed to cool naturally to the room’s ambient temperature (~75°F), the fuel-air ratio decreased at an average rate of 1.07 x 10-5 min-1 for the low-altitude test, it decreased at an average rate of 7.50 x 10-5 min, and for intermediate- and high-altitude scenarios, it decreased at an average rate of 1.58 x 10-4 min-1 and 2.08 x 10-4 min-1, respectively. Thus, as the ambient temperature is decreased, the rate of decrease in the fuel-air ratio increases.

David Blake

This technical note documents the number of incidents of cargo compartment smoke detector alarms on U.S.-registered aircraft operating under Federal Aviation Regulations (FAR) Part 121 and Part 135 for the years 1974 through 1999. The source for the data includes the Federal Aviation Administration (FAA) Service Difficulty Report System, the FAA Accident/Incident Reports, and National Transportation Safety Board (NTSB) accident information. The incidents are tabulated by year, precautionary action taken, cause, aircraft type, and phase of flight.