Many aircraft mechanics specialize in preventive maintenance.
They may examine an engine through specially designed openings while working from ladders or scaffolds, or use hoists or lifts to remove the entire engine from the craft. After taking the engine apart, mechanics may use precision instruments to measure parts for wear, and use x-ray and magnetic inspection equipment to check for invisible cracks. Worn or defective parts are repaired or replaced. They also may repair sheet-metal or composite surfaces, measure the tension of control cables, or check for corrosion, distortion, and cracks in the fuselage, wings, and tail. After completing all repairs, mechanics must test the equipment to ensure that it works properly.