R.G.W. Cherry & Associates Limited

The National Transportation Safety Board has recommended that fire suppression systems be installed in the cargo compartments of all cargo airplanes operating under 14 CFR Part 121. Currently, Class E cargo compartments, which are the primary cargo compartment type used in US cargo airplanes, do not require fire suppression systems. In response to this recommendation, FAA has requested that a cost/benefit analysis be carried out relating to the installation of on-board fire detection and extinguishment systems in cargo airplanes. This report contains the results of this analysis and a description of the methodology used.

The analysis assessed whether fire suppression systems, fitted to the cargo bays of cargo airplanes, type certificated to FAR Part 25 and operating under FAR Part 121, are likely to be cost beneficial. Potential benefits will result from a reduction in Injuries (Fatal and Serious) to personnel, a reduction in the damage incurred to the aircraft and its cargo, and a reduction in the damage that might be incurred to property on the ground. Potential costs are those that might be incurred from the installation and operation of fire suppression systems.

A mathematical model has been developed to assess the benefit. The model utilizes statistical distributions derived from data on in-service airplanes and accident information. Cost assessments were made for modifying cargo aircraft to the new Type F Cargo Compartment being considered for combi aircraft. These cost assessments were based on the installation of a Halon type fire suppression system together with suitable cargo compartment liners. The data used in the cost assessment was based on that contained in the ARAC document relating to main deck class B cargo compartments.

The results of the study suggest that crew injuries (Fatal and Serious combined) and the loss of the aircraft and cargo in freighter fire accidents are likely to be a significant factor in the prediction of benefit. Collateral ground damage does not appear to contribute significantly to the prediction of benefit. It is concluded that Halon fire suppression systems, or alternatives that are likely to be developed for below floor cargo compartments, are unlikely to be cost beneficial for the cargo compartments of cargo aircraft. Fire suppression systems, of the kind currently being considered for the cargo compartments of combi aircraft, may prove to be cost beneficial, particularly on larger cargo aircraft.

John W. Reinhardt and Robert Penman, III

This research was conducted to determine if a combination of Halon 1301 and nitrogen gas would prevent an aerosol can explosion. The aerosol can explosion simulation tests were conducted in the Pressure Fire Modeling Facility, at the Federal Aviation Administration William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. The aerosol can explosion simulator, used for the Aircraft Cargo Compartment Minimum Performance Standard, was mounted inside the instrumented pressure vessel that was located in this facility. The Halon 1301 and nitrogen were introduced to the pressure vessel using two different commercial off-the-shelf systems. The Halon 1301 gas was dispensed using a typical 20-pound fire bottle connected to a single nozzle via a 0.5-inch pipe. The nitrogen, used to reduce the oxygen volumetric concentration, was introduced to the pressure vessel via a hose connected to a ground-based inert gas generator. The aerosol can explosion simulator was activated once the desired concentrations of Halon 1301 and oxygen were reached, and it was pressurized at its designed (failure) value. The results showed that a clear benefit existed when Halon 1301 and nitrogen were combined below their inerting concentrations, thus preventing an aerosol can explosion.

Timothy R. Marker and Louise C. Speitel

This report summarizes the research effort undertaken by the Federal Aviation Administration to develop a laboratory-scale test method for evaluating the products of combustion inside an intact transport category fuselage during exposure to a simulated external fuel fire. An oil-fired burner, configured in accordance with Title 14 Code of Federal Regulations Part 25.856(b) Appendix F Part VII, was used to simulate the fuel fire, and a 4- by 4- by 4-foot steel cube box was used to mount representative test samples. The cube box simulated an intact fuselage and served as an enclosure to collect emitted gases during fire exposure. Test samples representing a variety of fuselage constructions were evaluated, including a noncontemporary prototype structural composite material (without thermal acoustic insulation). A typical cross section consists of a 40- by 40-inch aluminum panel representing the fuselage skin and the accompanying thermal acoustic insulation blanket behind the skin. Two thermal acoustical configurations were also tested. The first contained a heat-stabilized polyacrylonitrile fiber blanket. The second contained a ceramic paper barrier sandwiched under a fiberglass blanket. Each was encased by a thin metallized polyvinylfluoride moisture barrier. These burnthrough-resistant configurations were primarily run to provide a baseline for comparing the emitted gas concentrations with that of the prototype structural composite material.

A specialized Fourier Transform Infrared/total hydrocarbon gas analysis system was used to continually measure the products of combustion collected within the enclosure. Additional analyzers continuously measured the amount of carbon monoxide, carbon dioxide, and oxygen in the collected stream.

During the testing, it was determined that a prototype multi-ply structural composite material produced minimal quantities of toxic and flammable gases during a 5-minute fire exposure. Approximately 7 plies of the 13-ply composite material were delaminated by the fire exposure. By comparison, the aluminum skin/insulation configurations generated higher gas concentrations.

Subsequent full-scale testing of these material systems will provide gas scaling factors. The goal is to use this laboratory-scale test and scaling factors to predict decomposition products for an aircraft postcrash fuel fire.

Richard N. Walters and Richard E. Lyon

The flammability and mechanical properties of fiber-reinforced thermoset resin structural composites were evaluated. Processing characteristics, thermal stability, and flammability of the neat resins were measured using rheology, thermogravimetry, and pyrolysis-combustion flow calorimetry, respectively. Structural laminates were fabricated from liquid resins and woven glass fabric by vacuum-assisted resin transfer molding. Single-layer specimens (lamina) were prepared for fire testing using a hand lay-up technique. Mechanical properties of the laminates were measured in three-point bending. Fire behavior of the lamina and laminates was measured according to Title 14 Code of Federal Regulations 25.853(a-1) and Military Standard MIL-STD-2031. Results for flammability, fire performance, and mechanical properties of these composites are presented in this report.

Steven M. Summer

The Fuel Tank Flammability Assessment Method (FTFAM) is a Federal Aviation Administration-developed computer model designed as a comparative analysis tool to determine airplane fuel tank flammability as a requirement of Title 14 Code of Federal Regulations 25.981. The model uses Monte Carlo statistical methods to generate flammability data for certain unknown variables over known distributions for a large number of flights. The FTFAM iterates through each flight, calculating the flammability exposure time of each flight given the data input provided by the user. Calculating this flammability exposure time for a sufficiently large number of flights results in statistically reliable flammability exposure data. These calculations can be performed by the user for virtually any type of airplane fuel tank (body tank, wing tank, auxiliary tank, etc.) both with and without a flammability reduction method being employed.

This report serves as a user’s manual for this computer model to assist the user in its operation and to discuss the permissible changes that may be made to this model specific to a particular fleet of aircraft. It is updated through version 10 of the FTFAM. The user should reference Advisory Circular 25.981-2A for additional guidance on when to use this model and for a discussion of interpretation of results.