Advisory Rulemaking Committee - Task Group 4

This report is the findings of the Fuel Tank Foam and Expanded Metal Products Task Group, which was formed as a portion of the Fuel Tank Harmonization Working Group activity established in January 1998. The FAA initiated this activity by the issuance of a Harmonization Terms of Reference entitled "prevention of Fuel Tank Explosions" on 16 December 1997. The Working Group's stated task was to study means to eliminate or reduce fuel tank flammability and to propose regulatory changes to the FAA Aircraft Rulemaking Advisory Committee.

David Blake, Timothy Marker, Richard Hill , John Reinhardt, Constantine Sarkos

This report describes recent research by the Federal Aviation Administration (FAA) related to cargo compartment fire protection in large transport aircraft. A gaseous hydrofluorocarbon, HFC-125, was compared to Halon 1301 in terms of fire suppression effectiveness and agent decomposition levels in the cargo compartment and passenger cabin during full-scale tests involving a bulk-loaded cargo fire. Also, a zoned water mist system was designed and evaluated against a bulk-loaded cargo fire. An exploding aerosol can simulator is being developed to provide a repeatable fire threat for evaluation of new halon replacement agents. The potential severity of an exploding aerosol can inside a cargo compartment and the effectiveness of Halon 1301 inerting was demonstrated. Tests were also conducted to determine the effectiveness of Halon 1301 against a cargo fire involving oxygen canisters. Finally, HFC-125 was evaluated for use as a simulant for Halon 1301 during cargo compartment approval testing to demonstrate compliance with applicable FAA regulations.

Fuel Flammability Task Group

This report documents the findings of a Fuel Flammability Task Group made up of recognized fuel and combustion specialists investigating the flammability and explosiveness of fuel within an aircraft fuel tank. The task group reviewed all available reports on the subject and met and discussed the data with technical experts from Boeing Commercial Airplane Co., California Institute of Technology, and the National Transportation Safety Board. The scope of the report includes jet fuel definitions and specifications, jet fuel flammability data, influences of various factors on fuel flammability, and predictive analyses and models for flammability. The report discusses the impact of this knowledge on the needs for in-flight fuel fire prevention.

W. Steven Johnson, Lawrence M. Butkus, Rodolfo V. Valentin

The increased numbers of bonded composite components and bonded repairs of cracked structures make knowledge of adhesive bonding crucial to aircraft design and life extension. This report covers an effort which focused on using fracture mechanics to evaluate the Mode I fracture and fatigue properties of several adhesively bonded aerospace material systems. The research concentrated on bond line cracking rather than fatigue crack growth in composite or metal adherends. Particular attention was paid to the environmental durability of bonded systems in use or intended for use on transport, fighter, and supersonic aircraft.

Analysis was performed using closed-form solutions as well as finite element analyses. Results were discussed with respect to their relevance and applicability to bonded joint design. Key results include the identification of significant degradation in some varieties of bonded joints subjected to long-term isothermal exposure under hot/wet conditions. The degradation was manifested by decreased fracture toughness and fatigue threshold levels.

Finite element analyses were performed on specimens with dissimilar adherends having complex geometries and thermally induced stresses in the bond line. A case study in which finite element analyses were used to relate the experimental results from this program with those of an independent project is also included. The analyses highlight the importance of using tapered adherends to avoid fatigue failures and show that typical aircraft skin stresses' are below experimentally obtained threshold values for the specimen geometries investigated.

Results of this study emphasize that the environmental durability of adhesively bonded joints is a key issue which must be considered by aerospace design engineers.

Robert McGuire, Dr. Tong Vu

A commuter category Beechcraft 1900C airliner was subjected to a vertical impact drop test at the FAA William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. The purpose of this test was to measure the impact response of the fuselage, cabin floor, cabin furnishings (including standard and modified seats), and anthropomorphic test dummies. The test was conducted to simulate the vertical velocity component of a severe but survivable crash impact. A low-wing, 19-passenger fuselage was dropped from a height of 11' 2" resulting in a vertical impact velocity of 26.8 ft/sec. The airframe was configured to simulate a typical flight condition, including seats (normal and experimental), simulated occupants, and cargo. For the test the wings were removed; the vertical and horizontal stabilizers were removed; the landing gear was removed; and the pilot and copilot seats were not installed. The data collected in the test and future tests will supplement the existing basis for improved seat and restraint systems for commuter category 14 Code of Federal Regulation (CFR) Part 23 airplanes.

The test article was fully instrumented with accelerometers and load cells. Seventy-nine data channels were recorded. Results of the test are as follows:

the fuselage experienced an impact in the range of 140-160 g's, with an impact pulse duration of 9-10 milliseconds the simulated occupants experienced g levels in the range of 32-45 g's with a pulse duration of 44-61 milliseconds the test was considered to be a severe but definitely survivable impact the fuselage structure maintained a habitable environment during and after the impact the seat tracks remained attached to the fuselage along the entire length of the fuselage all standard seats remained in their tracks after the impact all exits remained operable all the test dummies experienced lumbar loads in excess of the current maximum requirement found in 14 CFR 23.562(c)(2).