Cold Weather Operation: Some engine tips for the winter

There are different considerations when preparing an aircraft for winter depending on whether the owner/operator plans to operate the aircraft during the winter months or just store it.

Another important factor to consider in cold weather operation is engine preheating. In addition to difficulty starting the engine, failure to preheat an engine in cold weather can cause damage to the engine. It can lead to minor amounts of abnormal wear to internal engine parts and eventually to reduced engine performance and shortened TBO time. Lycoming recommends engine preheating anytime temperatures are 10 F. The exception to this is its 76 Series models that include the O-320-H and O/LO-360-E. It recommends preheating these engines when temperatures are below 20 F. The preheating system should be inspected for proper operation and any visible indications of defects.

Water contamination

Water contamination in the gas is another important issue to keep in mind. We need to be vigilant in ensuring excessive water is not present in the fuel. Unlike in warm weather where small amounts of water will not have a significant effect on engine operation, flying in freezing conditions makes any moisture in the system potentially dangerous. There are several things that can be done to prevent water from contaminating the gas. First of all, ensure all tanks are topped off whenever possible. The humidity in any air present in tanks that are not topped off is absorbed by the fuel. We should also ensure that all fuel caps are properly secured to prevent any rain or snow from contaminating the system. In addition, a vigilant fuel sampling/draining program can help ensure that any moisture present can be detected and removed before it adversely affects the engine. All fuel tanks and sumps should be drained before each flight.

While we are on the subject of fuel, there is one thing you need to be careful of — inadvertent fuel spills caused by temperature differentials. The problem occurs when an aircraft that is topped off and sitting out on a cold ramp (cold soaked) is taken inside a warm hangar for storage or maintenance. As the fuel warms up, it will expand. This can lead to fuel being dumped overboard, causing a fire hazard and a mess to clean up.

Oil breather

The crankcase breather deserves special consideration in cold weather preparation. The FAA reports that a number of engine failures have resulted from a frozen crankcase breather line which caused pressure to build up, sometimes blowing the oil filler cap off or rupturing a case seal, which caused the loss of the oil supply. The water, which causes the breather line to freeze, is a natural by-product of heating and cooling of engine parts. When the crankcase vapor cools, it condenses in the breather line subsequently freezing it closed. Before flight ensure that the breather system is free of ice. If a modification of the system is necessary, be certain that it is an approved change so as to eliminate a possible fire hazard.


Wet cell batteries require some extra attention during cold weather. They should be kept fully charged or removed from the aircraft when an aircraft is kept parked outside to prevent loss of power caused by cold temperatures and the possibility of freezing. If a battery is discharged because of hard starting conditions, don’t allow it to remain in a discharged state. Ensure that it is charged immediately to help avoid any damage to the battery.

These have been a few tips on helping your customers safely operate in cold weather. With proper preparation and maintenance, pilots can safely enjoy the unique flying experience that winter offers.

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