Why is Winter in Aviation so important? Aircraft are designed to fly optimum and effectively with an undisturbed and unaltered structure. In winter during cold icing conditions, snowfall, freezing rain and/or drizzle, moisture presence with cold temperatures close to zero degrees, it becomes extremely important for ground crew and pilots to assess the aircraft structure and engines. The most important parts include of course the wings, stabilisers, rudder tail, radome and engines. It is of primary importance that these parts are free of icing and obstruction prior to departure. Often very thin hoar frost is acceptable however if you notice conditions are such that icing will form on the aircraft, then it is better to coordinate and de-ice the aircraft before departure. This can also be quite a challenge assessing the conditions during the dark hours so if in doubt, it is always better to de-ice.
Why is it important? De-icing is important as ice formation on the critical aircraft surfaces like the wings deform the wing cross sectional shape and hence disturb the smooth airflow. This applies to the rudder and stabilisers as well. Formation of ice on engine intake and fan blades also cause disrupted air intake and could even lead to engine stalls and reduction in thrust effectivity. Further more turbulent disturbed airflow over the wings could result in loss of lift and therefore an increase in stalling speeds. Flying an aircraft intentionally anywhere near stalling speed is not recommended as it could further lead to loss of control and or even a crash if not recovered promptly and correctly. Disturbed airflow could also mean a higher lift off speed before you get airborne and this could lead to increased takeoff roll. When on a performance limited runway that is short, you could easily overshoot the runway and end the situation in catastrophe.
Best Practise? It is best to use the correct de-icing methods and fluids that can protect the aircraft from icing up until you can safely get airborne. Always pay attention to hold over times which depending on temperatures and type of precipitation can vary. This can be anything from 10 minutes to almost even 2 hours of protection. Also once de-iced and the engines are running, it is advisable to use the aircrafts built in icing systems e.g. engine anti-ice, window heating and so on. You every possible protection you have. Be aware to monitor your latest takeoff time possible before the icing protection expires as this could mean any further delays could mean you might have to de-ice the aircraft again. Also be aware of degrading external weather conditions as then the icing fluid protection times could be much lesser and this can easily go unnoticed. In icing conditions it is also best practise to calculate performance with maximum thrust using the maximum possible available runway. Once you are airborne, then use the aircraft anti-icing systems and try your best to avoid prolonged flight times in icing conditions.