For those of you who are “flying” home for the New Year, please check out the “Safety Guide for Flight Attendants in Cold Weather”!

The annual grand "human migration" - Spring Festival travel has begun. According to forecasts, my country's civil aviation passenger volume during this year's Spring Festival travel will exceed 80 million, which is expected to set a new record.

Safety is the eternal first theme in air transportation. Now in the coldest days of winter, rain and snow may occur at any time in most parts of the country, which really puts considerable pressure on the take-off and landing and flight safety of civil aviation aircraft, and also brings a lot of troubles to passengers who are eager to return home.

The adverse effects of low temperatures in winter on civil aviation flight safety are mainly reflected in two aspects: one is the impact on the aircraft itself, and the other is the impact on the flight environment.

1. Impact of ice accumulation on aircraft and solutions

(1) Where on an airplane is ice likely to form? What effects will ice formation have?

In the severe winter environment, the biggest challenge facing aircraft is ice accumulation. When an aircraft is parked outdoors, if it encounters rain, snow or high humidity at night, it is easy for ice to accumulate on the surface of the fuselage. If the ice is not removed in time, it will have many adverse effects on flight safety.

Failure to remove ice in time will bring many disadvantages to flight safety (Source: Xinhua News Agency)

1) Wing ice accumulation

Ice can change the aerodynamic shape of an aircraft. When the wings and tail are covered with ice, the surface roughness increases, which increases the flight resistance and reduces the lift. Experimental analysis found that even if the thickness of ice accumulation on the leading edge of the wing is only one millimeter, the flight resistance of the aircraft will increase by 40% and the lift will drop by 30%.

In addition, wing ice accumulation also has a serious impact on the aircraft's maneuverability. For example, once the control surface is iced, the mass distribution of the fuselage will change, and the force on the control stick will also change accordingly, greatly reducing the control efficiency. The ice accumulation hidden in the gaps between the control surfaces is even more dangerous, which can cause the control surface to get stuck, and even completely make the aircraft lose its control performance.

Workers at Guiyang Longdongbao International Airport are de-icing the wings (Source: Xinhua News Agency)

2) Engine ice accumulation

When the ambient temperature is below 5°C, the aircraft's engine air intake, compressor and other parts are very likely to freeze. On the one hand, ice accumulation in the air intake will greatly deteriorate the engine's aerodynamic performance, and on the other hand, ice accumulation on the compressor blades may fall off due to vibration, causing structural damage to engine parts. These will reduce the engine's operating efficiency and effective thrust, and in severe cases may even cause engine damage or shutdown, threatening flight safety.

3) Ice accumulation in other parts

In addition to the two most critical parts, the wings and the engine, the low temperatures in severe winter may also cause ice to form on other aircraft devices exposed to the environment. For example, ice accumulation may cause the antenna used to send and receive radio waves on the aircraft to malfunction, and the wireless navigation equipment on the aircraft may not work properly; if there is ice accumulation on the pitot tube, it is likely to distort the readings of important instruments such as the airspeed indicator and the barometric altimeter, making it difficult for the pilot to judge the actual flight status of the aircraft; ice accumulation on the landing gear is even more dangerous. If the landing gear cannot be retracted or extended due to ice accumulation, it will directly affect the safety of the aircraft during takeoff and landing.

Staff at Changchun Longjia International Airport remove ice and snow from an aircraft (Source: Xinhua News Agency)

(2) How do aircraft remove ice?

1) Artificial de-icing

In order to ensure flight safety in winter, airlines will conduct ice inspections and de-icing operations before the aircraft takes off. If ice is found on the fuselage, ground staff will use a special de-icing vehicle to handle it. Ground staff first use a de-icing device to remove ice from the wings and other parts, and then spray antifreeze made from ethylene glycol or propylene glycol onto the fuselage at a high speed. This antifreeze needs to be heated before spraying, which can effectively lower the freezing point of moisture on the surface of the aircraft and will not freeze even at minus 16°C. However, manual operations will undoubtedly increase ground support time, which is likely to cause flight delays, and the number of flights that the airport can arrange each day will also be reduced.

Changan Airlines carries out winter de-icing work (Source: Xinhuanet)

2) Mechanical deicing

Modern aircraft have already taken anti-icing into account when they were first designed and manufactured. Heating devices are installed on the wings, tail, leading edge of the engine air inlet and other parts that are prone to ice formation to ensure that these parts will not ice up regardless of the weather conditions. For example, most passenger aircraft such as the Airbus 320 and Boeing 737 use the bleed air system to direct the hot air from the engine to the leading edge of the wing, while the Boeing 787 and others attach electric heating pads to the inner wall of the leading edge of the wing to achieve precise heating through electronic regulators.

Schematic diagram of the principle of electric heating anti-icing (Source: "Current Application Status and Technical Difficulties of Electric Heating Anti-icing/De-icing for Civil Aircraft Wings")

In recent years, aviation engineers have also found new anti-icing inspiration from lotus leaves. In life, we often see that when water drops fall on the surface of lotus leaves, they do not adhere to the lotus leaves, but gather into balls and roll down. This is the lotus effect. If we can create an aircraft structure surface that does not stick to water droplets like lotus leaves, it will undoubtedly be the most direct and effective anti-icing method. However, this anti-icing technology currently only exists in the laboratory, and it will take some time before it can be maturely applied in engineering.

2. Impact of low temperature weather in winter on the flight environment and solutions

( 1 ) Low temperatures in winter may also affect runways and visibility

Under the power of strong cold air in winter, the surface temperature drops sharply. If there is a lot of rain and snow, the airport runway will inevitably freeze. Snow or ice on the runway will cause the friction between the aircraft tires and the ground to drop sharply, and the take-off and landing distance will increase greatly, which may easily cause the aircraft to deviate from the direction or run off the runway.

In addition, rain and snow will seriously reduce visibility and affect the pilot's sight. In this regard, foggy weather is no less serious. Visibility is one of the main bases for the crew to judge whether it can take off normally, and it is also one of the key factors for the normal operation of the airport. The most dangerous stage of the aircraft during the entire flight is the take-off and landing stage, during which the aircraft's maneuverability will decrease. Due to the slow temperature rise in winter, the fog dissipates more slowly, and the low visibility it brings will undoubtedly hinder the pilot from seeing the surrounding objects and runway markings clearly, further threatening the safety of aircraft take-off and landing.

In November 2021, Harbin Airport was closed due to ice (Source: Webpage screenshot)

( 2 ) How to deal with runway icing and foggy weather?

For snow and ice accumulation on runways, major airports have comprehensive snow and ice removal solutions, such as using de-icing vehicles equipped with snow scrapers, snow brushes and de-icing agents to clean the runways, using high-temperature hot air to melt the snow and ice, or using high-pressure water to wash away the snow and ice on the runway surface.

However, if rain and snow continue for a long time and the ice and snow on the runway cannot be cleared in time, or if rain, snow and fog make visibility too low, the flight can only be canceled or postponed and released after the weather improves.

Airport staff clearing snow on the apron (Source: Xinhua News Agency)

3. Tips for safe flying in winter

At present, civil aviation has already perfected its measures to deal with rain, snow and fog in winter. Flights will be released only when flight safety is ensured, so passengers do not need to worry too much. Here are some tips for safe flight in winter. I hope everyone can return home safely and have a happy New Year.

(1) Pay attention to the weather conditions at the departure and destination locations on the day of your flight . If it is raining or snowing, the speed of public transportation will inevitably slow down. It is recommended to take the subway as much as possible. If you drive or take a special car to the airport, you must leave earlier than usual. If it is raining, snowing or foggy, you must also be prepared for flight delays or even cancellations.

Dalian Metro Line 5 Dalian Station (Source: Xinhua News Agency)

(2) Passengers need to board the plane before de-icing, so the waiting time in the cabin will be longer than usual . This is because although antifreeze will be sprayed after de-icing, the validity period of antifreeze is short. After de-icing, the plane needs to take off as soon as possible and cannot wait for passengers to board. It is also necessary to say that the air conditioning in the cabin will not be turned on during the de-icing period. The temperature in the cabin may be low while passengers are patiently waiting, so be sure to bring spare clothes with you to keep warm.

Please keep warm in the cabin (copyright image of the library, reprinting may cause copyright disputes)

(3) Winter has always been a high-incidence season for respiratory diseases and sudden illnesses among passengers on board. Currently, a variety of respiratory diseases are rampant. The terminal is crowded, the temperature difference between indoor and outdoor is large, and the aircraft is in a high-altitude low-pressure zone during the cruising phase. Passengers may feel unwell while flying. It is recommended that you wear a mask and prepare some common medicines.

During the peak period of respiratory diseases, it is recommended to wear a mask when taking an airplane (copyrighted image from the gallery, reprinting and using may cause copyright disputes)

(4) When walking on the road or getting on or off shuttle buses or bridge elevators in rainy or snowy weather, passengers must hold the railings tightly and walk slowly to avoid slipping . Ladies should try not to wear high heels.

(5) There are more strong winds in winter, and the aircraft may experience turbulence during flight. Passengers should secure their luggage and clothing immediately after boarding the aircraft , and be sure to fasten their seat belts to prevent damage caused by sudden turbulence.

Author: Zhu Lei, PhD in Aerospace Propulsion Theory and Engineering, Nanjing University of Aeronautics and Astronautics

Reviewer: Deng Xiaotao, Senior Engineer, AECC Hunan Power Machinery Research Institute

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.