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Avionics equipment, especially for safety-critical systems, is developed by means of a series of design steps, propagating and refining requirements through a number of hierarchical levels, from the aircraft level, through system and sub-system levels, down to equipment, subassemblies and individual components (see SAE ARP4754A [11]). At each development level, accompanying safety assessments (e.g. per SAE ARP4761 [12]) are performed to derive safety requirements which ensure compliance to the overall safety requirements determined by the aircraft and systems functional hazard assessments (FHAs). The safety related requirements of all development levels flow through the process down into the individual equipment specifications and are ultimately implemented in the equipment design where the design data is approved for the certificated aircraft (or engine) type. The equipment production process builds the equipment according to this approved design data.

Fault tree analyses and the associated safety assessment process plays an essential role in demonstrating acceptable avionic system compliance to the system safety requirements derived from safety related regulations associated with the civil aircraft certification process (e.g. 14CFR/CS §25.1309). SAE ARP4754A and SAE ARP4761 are established industry guidelines for the safety process and fault tree methodology applicable to civil aircraft certification based on techniques which have now been in use for decades. System model-based techniques, used for some time in system and software development, are now being applied in the safety assessment process. These system behavior models of functions with their associated dependencies and assignments have been supplemented with failure modes and effects to “automatically” generate fault tree like outputs. These system model-based fault trees are intended to become integral to the safety assessment process.

The latch body is a safety critical 4340 steel part that is currently used in the cargo hook of a CH-47 military helicopter. Approximately 5×2×2 inches in dimension, this safety critical part is nestled within the cargo hook assembly and facilitates the operation of the load beam (hook) during its payload cycles. This paper mainly focuses on the methodology and design advantages of converting a wrought two piece latch-body into a single piece machined component. The application of austempering heat treatment to improve mechanical properties and eliminate surface cracking vis-à-vis generic oil quenching and tempering treatment is discussed. The application of laser technology for surface hardening of the austempered latch body is reported. Mechanical testing of austempered 4340 steel, microstructural examination, characterization of the laser and induction hardened layers, and preliminary testing to evaluate the integrity of the hardened layers is presented.

Heat treated 7000-series aluminum alloys exhibit the highest strength and toughness amongst wrought aluminum alloys, and are used for a variety of applications in the defense and the aerospace industry. The corrosion resistance of these alloys is strongly dependent on final thermo-mechanical and tempering treatment. Many surface modification techniques are used to protect these alloys against general, exfoliation and pitting corrosion. Hard anodizing is a surface modification technique that imparts corrosion and wear resistance to 7000-series aluminum alloy parts. However, if the anodized parts experience cyclic loading conditions, there is a risk that the brittle anodized layer may undergo cracking thereby compromising the corrosion resistance of the 7000-series aluminum components in service.

Optimized 1997 model year Caterpillar C10 dual-fuel natural gas engines certified to the California Air Resources Board's Alternative Low NOx 2.5 gram/brake horsepower-hour emission standard were demonstrated in three commuter buses over a 12-month period, in Santa Barbara, California. The project evaluated the retrofit costs and process, performance, reliability, fuel economy, operating costs, and emissions of the three C-10 dual-fuel natural gas engines compared to a standard C-10 diesel engine. Chassis dynamometer tests using the U.S. EPA Urban Dynamometer Drive Schedule, the Central Business District (West Virginia University version) and the 55-mph Steady State cycles were conducted to characterize in-use emissions of the dual-fuel engines for the commuter bus application. During 94,000 combined service miles, performance, reliability and durability of the dual fuel buses were similar to the diesel control.