De-ice

The aircraft de-icing (English de -icing ) is a process in which a plane of ice and snow is freed. De-icing is required for security purposes, to increase snow and ice the aircraft weight and influence the aerodynamics unfavorable.

  • 2.1 Electric De -icing
  • 2.2 Mechanical De -icing
  • 2.3 Chemical anti -icing
  • 2.4 Thermal anti -icing

De-icing on the ground

The de-icing of aircraft on the ground must not be with the de-icing of the soil itself, the surface de airports, confused.

Before the start of existing or which forms Eisansätze be removed by de-icing fluid or hot air. The start of the machine must be carried out immediately.

In addition, a protective layer may be applied (English anti -icing ), which prevents re- icing even with precipitation. The deicing used is a mixture of water, alcohol ( glycol ) and additives. The mixing ratio of water to de-icing liquid is dependent on the outside temperature, of the type of precipitation and the time required for the protective effect. Care is taken that the liquid is biodegradable and is collected. Reuse is usually not possible.

De-icing takes place with a big boom and a remote-controlled nozzle at the top on special positions (English deicing pads / deicing areas), and building positions or on the apron using special equipment.

The icing needs to be done right before the start, so as not to exceed the period of protection. In the winter, therefore, also occur in well-organized airports frequent delays in air traffic due to the necessary de-icing of aircraft on.

Deicing fluids

There are according to ISO / SAE four liquid types. Type II, III and IV consist of about 50 % glycol and 49 % water and can be used up to at least -25 ° C temperatures. They are mixed with thickeners, so they adhere better. Thus, the de-icing remains longer on the surfaces of the aircraft and may even swam similarly take a certain amount of winter rainfall and liquefy.

Such swollen Enteisungsmittelrückstände on the other hand at higher altitudes freeze again and, depending on how much of the volatile glycol content in the hygroscopic polymer ( thickener ) residues was replaced by water, then into the rudder columns block the control surfaces and limit the controllability of the airplane. The consistency of these residues has then ( at this temperature could turn a container filled with the substance cup without anything flowing out ) between -57 ° C ( almost 100 % glycol ) and 0 ° C ( then would all glycol units replaced a so-called pour point by water ). This phenomenon occurs mainly after long winter dry periods on with the subsequent onset of precipitation in the form of rain or temperature inversions. Therefore, it is important to remove these residues regularly thoroughly.

The time at which the aircraft is being protected from refreezing is, derivative time (English holdover time ( HOT) ) called. The HOT depends on the nature of the precipitate, the local temperature ( engl. outside air temperature, OAT ) and the thickness of the precipitate. Is an aircraft with eg snow contaminated, decided solely by the pilot or one of his authorized representative, if the aircraft is de-iced. Also on the mixing ratio of de-icing the pilot decides. The three types II, III and IV are diluted to the required protection at fixed mixing ratios with water or remain undiluted: 100 %, 75 % or 50% will be applied.

The types II, III and IV differ in the thickeners used. Type III is starting for slow ( <85 knots ) Aircraft ( rarely used), type II and type IV for faster machines is of type II with a larger shear and heat resistance and a longer lead time.

The deicing type I does not contain this thickener and is therefore good for Deicing or ( restricted ) for anti -icing with pure frost conditions suitable without precipitation. It consists of about 80 % glycol and 20% water and is diluted according to the prevailing weather conditions with water. It can therefore be used even at very low temperatures.

In the so-called " two-step de-icing " is any ice or snow, depending on the prevailing outside temperature, with hot water or a mixture of type I or type II and water away from relevant areas and then a protective layer ( anti -ice ) coated with type II, III or IV.

Infrarotenteisung

In Newark (USA) and from January 2006 in Oslo a Infrarotenteisungsanlage is employed. Aircraft are de-iced up to a size of an Airbus A320 or a Boeing 737 in a hall with the heat from infrared lamps. After that they can be protected in the hall by the application of an anti - icing fluid against re-icing. This procedure is considered environmentally friendly and is subject to contamination of the aircraft with wintry buildup also quite fast.

Gantry

The gantry was a steady de-icing at the airport Munich ( MUC). It was developed in the late 80s and came in eight winter seasons used. The aircraft were towed it into the machine and de-ices there.

In 2001, she would need to be upgraded due to the lack of suitability for aircraft with winglets and larger aircraft such as the Boeing 777, Boeing 747 or the Airbus A380. However, mobile deicing vehicles today need less staff and are more cost efficient - thus the modernization would not have been worth it. Today the plant is reduced.

De-icing in the air

Also in the air between de -icing ( German ice removal ) and anti- icing ( German Eisverhinderung ) is distinguished.

Aircraft that are certified for IFR flights in icing conditions (ie, inter alia, the vast majority of passenger aircraft ), have mostly on the wing leading edges, engines and other areas where ice accretion may be more dangerous form, heated surfaces.

Electric De -icing

For propeller aircraft de-icing is done by heating by electricity or by boots ( see below). The energy requirement for a thermal de-icing by current is extremely high. Therefore, this method is used rather than emergency procedures. In order not to overwhelm the electrical performance of the airplane, only individual heating surfaces are always (in pairs, symmetrically ) and not all at once at intervals on ( eg 5 minutes). The problem is unbalanced de-icing of the propeller, which can then lead to strong vibrations ( at 2500 rpm, for example, 42 Hz), which can damage the engine, among others. For strong vibrations immediately is the speed to reduce as far as possible. Therefore, it is advisable to avoid the formation of ice (freezing ) completely. In case of electrical de-icing on the four- bladed propellers two opposite propeller blades must be de-iced at the same time.

Slices of the glazing be de-iced with embedded resistive layers or wires.

Forschungszentrum Karlsruhe and DaimlerChrysler Aerospace Airbus have a de-icing means of microwaves is described which is suitable for plastic and composite materials.

Mechanical de-icing

Smaller machines have still at risk points on rubber mats (English boots ) that are cyclically inflated by compressed air during the flight and so can blow off ice accumulation.

Chemical anti -icing

Alternatively, it is also de-icing systems, which expel at risk points deicing fluid ( isopropanol or glykolhaltig ) of fine holes. In this way, ice formation is prevented, but the maximum lifetime is limited by the tank size. This de-icing is used particularly for propeller.

Thermal anti -icing

For jets that deliver with their engines enough waste heat, the heating is done by bleed air from the engine (thermal anti- ice - TAI ). The very hot bleed air is blown through the hollow space behind the wing leading edge. The heat can weaken and damage the material (aluminum). Therefore, the temperature needs to be monitored in this sector. At the bottom thermal anti- ice may not be used, since the cooling air Wind is missing. For a start thermal anti- ice and off as possible so as not to deprive the engine starting power. In case of failure of an engine during start could the critical difference between "Start with an engine " and " accident during launch " make up because of the bleed air for thermal anti- ice the missing power. The same is true for landing because the pilot must always be prepared for a go-around.

For airplanes with reciprocating engines, often serves a carburetor heat to prevent carburetor icing.

Accidents

  • American Eagle Flight 4184 - Freezing rain which froze on the wings to ice and worsened the aerodynamic characteristics of the wing, could not be removed by the de-icers. As a result of ice formation and the disruption Profilumströmung there was an aileron torque reversal that brought the aircraft into an uncontrolled situation. The pilots it has not been possible to bring the machine back under control.
  • Air Ontario Flight 1363 - The machine had not been de-iced, as the engines because of a defect APU could not be turned off and the aircraft - a Fokker F-28 - could not be de-iced in accordance with the requirements of manufacturers and airlines with the engines running.
  • USAir Flight 405 - After start-up delays, the machine was not de-iced again, although this would actually have been necessary. The crew overlooked hazardous ice deposits on the wings and tail, and thus gave a more de-icing to be unnecessary.
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