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Aircraft Construction and Structural Materials
In a effort to help ensure personnel safety, airport firefighters should have a thorough knowledge of aircraft construction, the materials used, and the hazard they may pose during and after fire fighting operations. The inherent properties of the materials and the manner in which these components are assembled may effect fire fighting operation. Material commonly used in late-model aircraft constructions include metals such as aluminum , steel, magnesium, and titanium; composite material and metal alloy; plastics; and wood. These materials are often used in any number of combinations. ARFF personnel should be aware that when the surfaces of different materials are uniformly painted, the variation in construction may not be apparent without close investigation.
A. METALS A number of metals are utilized in the construction of aircraft. The most common metals is used in aircraft include aluminum and aluminum alloys, steel, magnesium and magnesium alloys, and titanium. The sections that follow discuss how these metals are employed in aircraft constructions.
B. Aluminum and Aluminum Alloys Due to its lightweight characteristics, along with the ability to be molded into a variety of shapes, aluminum has been an ideal material for aircraft constructions. This lightweight material also can be molded and used in sheets for skin surfaces, or it can be formed into honeycomb sheets, which are often used to form wall and floor sections. One disadvantage to using aluminum for aircraft constructions is that it does not withstand heat well; it melts at relatively low temperatures [approximately 1,200 degrees F {649 degrees C}]. Aluminum alloys are created by mixing components of different types together in a molding process that produces stronger, yet lighter constructions material. These alloy can be found molded into landing gear parts, structural and load-bearing members, as well as parts of the door operating assemblies. The most common alloys currently used in the constructions of aircraft include aluminum-beryllium and aluminum-lithium. The percentage of aluminum used in aircraft constructions continues to decrease as new, composite materials are developed to replace it.
C. STEEL In certain parts of the aircraft, such as in the engine and landing gear, high strength in required and/or high tolerance is critical. Steel is used in these components, even though the weight of steel per volume is much higher than other structural materials.
D. Magnesium and Magnesium Alloys Because they are both strong and lightweight, magnesium and magnesium alloys are used for the landing gear, wheels or some older aircraft, engine-mounting brackets, crankcase sections, cover plates, and other engine parts. Magnesium and its alloys are generally used in areas where forcible entry will not be required. Unless ground into a dust or into small particles, magnesium is difficult to ignite; however, once ignited, it burns intensely and is very difficult to extinguish.
E. TITANIUM Titanium is a metallic element used to reinforce skin surfaces against impinging exhaust flames or heat. Titanium is used for internal engine part such as turbine blades, auxiliary power unit enclosures, and landing gear part. Like magnesium, titanium is a combustible metal that burns with intensity and makes extinguishment difficult