Knowledge of aircraft fuel systems, and basic electrical and mechanical principles to plan, lay out, and perform work involving the repair, test, installation, and maintenance of complex aircraft fuel systems designed to adjust automatically to factors such as temperature, humidity, pressure, or rate of change of velocity, or have sensing devices that feed back into the system information on the systems performance. Frequently exposed to loud noise from the movement of machinery and test equipment; to the possibility of cuts, burns, electrical shock, and bruises from moving parts of machinery; and to unpleasant conditions from dirt, grease, fuel, toxic fumes, solvents, and gases, Various protective devices such as air supplied respirators, gloves, ear plugs, face shields, safety shoes, and safety glasses are used.