During train inspections, engine personnel must use their senses of sight, hearing, touch, and smell to examine the condition of the main components and ensure all parts and lines are functioning properly. Train inspections are generally classified into levels 1, 2, 3, and 4. Depending on the level, detailed inspections and repairs are implemented on items such as the power system, transmission system, running gear, braking system, electrical and instrumentation, bodywork, and couplers.