Frequency Of Flight And Its Effect On The Engine

We have firm evidence that engines not flown frequently may not achieve the normal expected overhaul life. Engines flown only occasionally deteriorate much more rapidly than those that fly consistently. Pilots have asked, "What really happens to an engine when it’s flown only one or two times per month?" An aircraft engine flown this infrequently tends to accumulate rust and corrosion internally. This rust and corrosion is often found when an engine is torn down. Some operators are running the engines on the ground in an attempt to prevent rust between infrequent flights. This may harm rather than help the engine if the oil temperature is not brought up to approximately 165o F, because water and acids from combustion will accumulate in the engine oil. The one best way to get oil temperature to 165o F is fly the aircraft. During flight the oil normally gets hot enough to vaporize the water and most acids and eliminate them from the oil. If the engine is merely ground run, the water accumulated in the oil will gradually turn to acid, which is also undesirable. Prolonged ground running in an attempt to bring oil temperature up is not recommended because of inadequate cooling that may result in hot spots in the cylinders, or baked and deteriorated ignition harness, and brittle oil seals causing oil leaks. If the engine can’t be flown, then merely pull it through by hand or briefly turn the engine with the starter to coat the critical parts with oil. If the engine is flown so infrequently that it does not accumulate the operating hours recommended for an oil change (25 hours for a pressure screen system and 50 hours for a full-flow filter system), then the oil should be changed at four-month intervals to eliminate water and acids.