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.

William M. Cavage

This report documents a cost analysis of ground-based fuel tank inerting for the commercial fleet performed by a group of industry experts lead by an Federal Aviation Administration (FAA) representative. Ground-based inerting (GBI) consists of displacing most of the oxygen dissolved in the fuel with nitrogen by a process called fuel scrubbing, and displacing the air in the empty space (ullage) of the fuel tank, with nitrogen-enriched air (NEA) in a process called ullage washing. The cost analysis considers the cost of implementing and performing GBI for all US departures carrying more than 19 passengers. The cost of GBI for only departures of airplanes with heated center wing tanks (HCWTs) was also determined. Airplanes that have the air conditioning equipment, or packs, located below the center wing fuel tanks are considered to have heated center wing tanks. This analysis considered all nonrecurring and recurring costs of GBI at all major U.S. airports over 10 years, with a 3-year start-up period. The cost of modifying the aircraft to allow for GBI was not considered in this analysis.

Compiled by April Horner

The purpose of the Aircraft Materials Fire Test Handbook is to describe all FAA-required fire test methods for aircraft materials in a consistent and detailed format. The handbook provides information to enable the user to assemble and properly use the test methods. Moreover, to broaden the utility of the handbook, the appendices contain the following information: FAA fire safety regulations, FAA approval process, aircraft materials, regulatory methodology used by other countries, aircraft industry internal test methods and guidelines, laboratories actively using fire test methods, and commercial manufacturers of fire test equipment.