Winter flying between risk and fascination
Flying in winter requires more preparation than in the summer months. Many factors that hardly play a role in warm weather can now become relevant to safety. Snow, ice, frost and low temperatures affect aerodynamics, engines, instruments and ground operations. However, the additional effort is offset by a special attraction: calm air due to the lack of thermals, excellent climb performance thanks to high air density and spectacular views of snow-covered landscapes.
It is crucial to realistically assess the typical winter risks and to consistently include them in the planning and execution of a flight.
Weather analysis in winter: Small differences with a big impact
The weather assessment basically follows the same principles as in summer, but has a different weighting in winter. Precipitation, which appears harmless at favourable temperatures, can quickly become decisive for flight in the cold season. Snow showers can abruptly reduce visibility and make visual flight conditions unusable within a few minutes.
Supercooled rain is particularly critical. Large droplets from clouds with temperatures around freezing point can suddenly freeze and form clear ice when they hit the surface of the aircraft. This type of ice is particularly dangerous as it is difficult to recognise, builds up quickly and massively impairs aerodynamics. Drag increases, lift decreases and the minimum speed increases.
Rough ice from supercooled water droplets in stratus clouds also poses a considerable risk. It tends to form on the leading edges of wings and tail units and can not only reduce lift, but also alter control behaviour.
Consequences for flight planning and range
The more weather-related uncertainties there are, the more important alternatives become. Alternate aerodromes should be carefully selected and realistically accessible. Fuel reserves become even more important in winter, as does the available daylight hours, which are significantly shorter than in summer.
Planning with tight margins pays off more quickly in the cold season. A planned flight that takes longer due to weather diversions can otherwise inadvertently lead into twilight or darkness.
Emergency preparedness: preparing for an emergency
A winter flight should always be considered from the point of view of a possible outlanding. Cold, snow and wet conditions pose a serious risk to people and equipment. Appropriate emergency equipment should be on board, including warm clothing, gloves, a hat and, if necessary, simple aids to keep warm.
The decision on what to take with you should not be based on the performance of the cabin heating, but on what would be necessary outside the aircraft.
Ground operations and aircraft preparation
In winter, significantly more time must be allowed before take-off, especially for aircraft parked outside. Snow, ice and frost must be completely removed from the outer skin. Even thin frost on the wings or tail unit acts like sandpaper on the airflow, reduces lift, increases the stall speed and worsens the overall flight behaviour.
An aeroplane is aerodynamically dependent on a clean surface. Unlike a car, it is not just a single contact point that is relevant, but the entire structure around which the air flows. Lift, drag, stability and controllability depend directly on this.
Correct removal of snow and ice
Soft hand brushes, brushes or textile cloths are suitable for cleaning. Ice scrapers can damage the paintwork and especially the glazing. Special care should be taken on window surfaces, as scratches can impair visibility and structural strength.
The use of TKS liquid from a spray bottle has proven to be effective. Car de-icers should be avoided as they can attack materials. When cleaning, care must be taken to wipe snow and ice away from rudder and flap gaps to prevent penetration and subsequent freezing. The pitot tube and static openings must be carefully checked and completely clear.
A heated hangar or at least sunlight makes the work considerably easier, but requires time and planning.
Preparing for take-off in sub-zero temperatures
Cold temperatures have a direct effect on the engine and battery. Viscous engine oil increases the starting resistance, weak batteries make starting more difficult. Preheating the engine is recommended at the latest at temperatures below around minus six degrees. Warm air blowers, which are fed into the cowling via hoses, significantly reduce the load on the engine.
Batteries should be removed, stored in a frost-free location and charged regularly when not in use for long periods. An external jump-start may enable starting, but does not guarantee that all electrical systems are sufficiently supplied to safely start generator operation.
Carburettor fire and cold start risks
Several unsuccessful attempts to start the engine with excessive fuel supply can lead to carburettor fires. Typical signs are vaporising oil residues or smoke in the engine compartment. In this case, pull the mixture lever immediately and continue to operate the starter motor to draw the flames into the engine, where they lack oxygen.
Such scenarios emphasise the importance of clean starting procedures and patience during cold starts.
Rolling and take-off on slippery slopes
The journey to the runway should be made slowly and without unnecessary use of the brakes. Brakes can cause the wheels to lock on snow or ice and cause uncontrolled skidding. Particular care should be taken with low-wing aircraft, as snow drifts or piles of snow pushed up under the wings by snow clearing vehicles can become a problem.
On the runway, a track should be selected where both main landing gears have the same surface. Different coefficients of friction, for example between snow, ice and open tarmac, can lead to yawing and a tendency to break away. Gentle power build-up helps to keep the direction under control.
Realistically plan for longer starting distances
Snow, slush or standing water can increase the take-off distance considerably. If the flight manual does not state specific values, conservative allowances should be factored in. Depending on the type and condition of the surface, 25 to 50 per cent additional distance can be realistic. The point at which a take-off abort must be initiated is also shifted accordingly.
Aircraft with retractable landing gear should initially leave the landing gear extended after take-off so that any snow or ice adhering to it can be thrown off. Ice in the landing gear shaft can block sensors and lead to false readings.
Icing in flight and the carburettor as a weak point
In winter, even IFR pilots avoid areas with visible humidity at negative temperatures if possible. This is all the more true for VFR flights. Icing can often be recognised indirectly, for example on struts, antennas or external temperature sensors, if the wings themselves are not visible.
However, the engine can be affected even before structural icing occurs. Carburettor icing occurs in humid air even at surprisingly high temperatures. Erratic running, loss of engine speed or falling boost pressure are warning signs that require the carburettor preheater to be pulled immediately. Preventive activation at regular intervals can help to recognise ice formation at an early stage.
Conclusion: Winter flying requires discipline and knowledge
Flying in winter is not a question of courage, but of preparation, technical understanding and realistic decision-making. Those who are aware of the particular risks, have sufficient time, reserve and respect for them and are prepared to consistently cancel or postpone flights will also be safe when flying in the cold season.
Winter rewards those pilots who take it seriously - with calm air, outstanding performance and unique impressions from the cockpit.
Source references:
Aviation magazine
