Inoperative Overspeed Safety Devices Overspeed safety devices are designed to shut off fuel or air in case of excessive engine speed. These devices must be maintained in operable condition at all times. Inoperative overspeed devices may also cause an engine not to start. They may be inoperative because of improper adjustment, faulty linkage, or a broken spring, or the overspeed device may have been accidentally tripped during the attempt to start the engine. If the overspeed device fails to operate when the engine overspeeds, the engine may be secured by manually cutting off the fuel oil or the air supply to the engine.
Most engines have special devices or valves to cut off the air or fuel in an emergency.
If the engine cranks slowly, the necessary compression temperature cannot be reached. Low starting air pressure may be the cause of such trouble. Slow cranking speed may also be the result of an increase in the viscosity of the lubricating oil. This trouble occurs during periods when the air temperature is lower than usual. The oil specified for use during normal operation and temperature is not generally suitable for cold climate operation.