Aircraft de-icing
The aircraft de-icing (Engl. De-icing ) is a process in which a plane of ice and snow is freed. De-icing is necessary for safety reasons, because ice and snow increase the weight of the aircraft and have an adverse effect on aerodynamics .
De-icing on the ground
Before the start, existing or forming ice deposits are removed using de-icing fluid or hot air. The machine must then be started immediately.
In addition, a protective layer can be applied ( anti-icing ), which prevents renewed ice formation even when it rains . The deicing agent used is a mixture of water, alcohol ( glycol ) and additives. The mixing ratio of deicing fluid to water depends on the outside temperature, the type of precipitation and the time it takes to provide protection. It is ensured that the liquid is biodegradable and is collected. Reuse is usually not possible.
De-icing takes place with special devices with a large boom and a remote-controlled nozzle at the tip either on special surfaces ( deicing pads / deicing areas ) that are controlled by the aircraft via the runway ( remote de-icing ) or directly on the parking position (English gate de-icing ) on the building or on the apron .
De-icing must be carried out immediately before take-off in order not to exceed the protective effect time. In winter, therefore, even at well-organized airports, there are more delays in air traffic due to the need to de-icing the aircraft.
De-icing fluids
There are four types of fluids according to ISO / SAE . Types II, III and IV consist of about 50% glycol and 49% water and can be used at temperatures down to at least −25 ° C. They have thickeners added so that they adhere better. As a result, the aircraft deicing fluid (ADF ) stays longer on the surfaces of the aircraft and can even absorb a certain amount of winter precipitation and liquefy it like a sponge.
On the other hand, such swollen deicing agent residues can freeze again at greater heights and, depending on how much of the glycol content in the hygroscopic polymer (thickener) residues was replaced by water, then block the control surfaces in the rudder gaps and limit the controllability of the aircraft. The consistency of these residues then has a so-called pour point (at this temperature you could turn a beaker filled with the substance without anything flowing out) between -57 ° C (almost 100% glycol) and 0 ° C (then all glycol components would be replaced by water ). This phenomenon occurs mainly after prolonged winter dry periods with subsequent precipitation in the form of rain or inversion weather conditions. It is therefore important to thoroughly remove this residue on a regular basis.
The time in which the aircraft is protected against re-icing is, Derivative (Engl. Holdover time, HOT ) called. The HOT depends on the type of precipitation, the local temperature ( outside air temperature, OAT ) and the strength of the precipitation. Is an aircraft with z. If, for example, snow is contaminated, the pilot or someone authorized by him alone decides whether the aircraft is de-iced. The pilot also decides on the mixing ratio of the de-icing fluid. The three types II, III and IV are diluted with water in fixed proportions according to the required protective effect or remain undiluted: 100%, 75% or 50% are used.
Types II, III and IV differ in the thickeners used. Type III is for slow (<85 knots) take off aircraft (rarely used), Type II for faster machines and Type IV corresponds to Type II with a greater shear and heat resistance and a longer lead time.
The type I deicing agent does not contain this thickener and is therefore well suited for deicing or (to a limited extent ) anti-icing in freezing conditions without precipitation. It consists of about 80% glycol and 20% water and is diluted with water according to the respective weather conditions. It can therefore also be used at very low temperatures.
With the so-called "two-step de-icing", existing ice or snow is removed from relevant surfaces with hot water or a mixture of type I or type II and water, depending on the prevailing outside temperature, and then a protective layer (anti-ice) with type II, III or IV applied.
The use of de-icing fluids can pollute the cabin air. During examinations of a passenger plane which showed abnormalities, propylene glycol concentrations of up to 2.5 mg / m 3 were found in the cabin air .
Infrared de-icing
In Newark (USA) and, since January 2006, also in Oslo , an infrared de-icing system has been used. Here, aircraft up to the size of an Airbus A320 or a Boeing 737 are de-iced in a hangar using the heat from infrared lamps. They can then be protected against re-icing in the hall by applying an anti-icing liquid. This process is considered environmentally friendly and, depending on the contamination of the aircraft with winter buildup, is also quite quick.
Gantry
The gantry (English frame, portal) was a stationary de-icing system at Munich Airport (MUC). It was developed in the late 1980s and was used in eight winter seasons. The aircraft were towed into the machine and de-iced there.
In 2001 it would have had to be modernized because it was not suitable for aircraft with winglets and larger aircraft such as the Boeing 777 , Boeing 747 or the Airbus A380 . However, mobile de-icing vehicles nowadays require fewer staff and are more cost-efficient - so the modernization would not have been worthwhile. Today the plant is dismantled.
Defrosting in the air
In the air, too, a distinction is made between anti-icing (German ice prevention) and de-icing (German ice removal).
Airplanes that are certified for instrument flights under icing conditions (including the vast majority of passenger planes) usually have heated surfaces on the leading edge of the wing, engines and other surfaces on which dangerous ice can form.
Electric and electromagnetic de-icing
Propellers are usually de-iced by heating them with an electric current. The energy requirement for this is high. In order not to overload the electrical power of the aircraft, only individual heating surfaces are always switched on in pairs symmetrically at intervals (e.g. 5 minutes). The problem is asymmetrical icing on the propeller, which can lead to strong vibrations; the speed should be reduced as much as possible. With electrical de-icing on the four-blade propeller, two propeller blades opposite each other are de-iced simultaneously.
Panes of the glazing are de-iced with embedded resistance layers or wires.
The Karlsruhe Research Center and DaimlerChrysler Aerospace Airbus have described a de-icing process using microwaves with a frequency of over 20 GHz that is suitable for fiber composite materials.
Pneumatic de-icing
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Even today, smaller machines still have rubber mats ( boots ) in the endangered areas , which are inflated cyclically by compressed air during the flight and can thus break off ice accumulation. Aircraft types in commercial air traffic with this device are, for example, the De Havilland DHC-8 , ATR 42 / ATR 72 , Saab 340 / Saab 2000 , Fokker 50 and Dornier 328 series .
Chemical-physical anti-icing
Alternatively, there are also de-icing systems that press de-icing fluid ( containing isopropanol or ethylene glycol ) out of fine pores at the endangered areas . In this way, ice accumulation is prevented or removed. However, the maximum duration of use is limited by the tank size. This de-icing process is based on freezing point depression (FPD) and is used for discs, wings and propellers.
Such as inflatable rubber mats had porous fabrics of Dunlop, could exit the de-icing fluid, the disadvantage of the slippage of steel ropes of barrage balloons along the wing leading edge towards (more per leaf) pyrotechnics blasting cable cutters to obstruct. For the use of the low-flying British RAF bombers in the Second World War over the German Reich, an armored leading edge of the wing was to be developed that could allow deicing agent to escape.
TKS is the brand name of the process, developed by TKS (Aircraft Deicing) Ltd. At the instigation of the British government, this new cooperation was formed in 1942 from 3 specialist companies with the initials T, K and S:
- Tecalemit Ltd. Lubricating systems produced, in particular metering pumps .
- Kilfrost Ltd. manufactured deicing chemicals.
- Sheepbridge Stokes (now part of the GKN Group ) produced newly developed porous metal materials based on powder metallurgy .
The developed "de-icing strip" consists of a tube with about half an inch (1.27 cm) square cross-section, the front of which is formed by porous sintered metal and went into production towards the end of the Second World War (around 1945) . The Handley Page Halifax , Avro Lincoln and Vickers Wellington bombers were equipped with it .
Around 1950, TKS introduced more efficient porous panels for this function, made from NiRo steel powder and later rolled and sintered wire mesh. The latter is still produced today. A term for this is weeping wing .
In the 1970s the idea to use laser drilling came up, in the 1980s titanium sheet drilled in this way appeared. The following construction on the wing nose is still in use today: 0.7–1.2 mm thin titanium sheet with 124 laser holes per square centimeter with a 0.064 mm diameter, backed by a porous membrane for evenly distributing the de-icing fluid, which is supplied via nylon tubes of 14- or 28-volt pumps with 40–55 watts of power are supplied from a tank.
In 1994 TKS was acquired by Aerospace Systems & Technologies (AS&T).
Thermal anti-icing
In the case of jet airplanes, which generate sufficient waste heat with their engines, the heating is done by bleed air from the engine ( thermal anti ice, TAI ). The very hot bleed air is blown through cavities behind the leading edge of the wing. The heat can weaken and damage the material ( aluminum ). Therefore, the temperature in this area must be monitored. Thermal anti ice must not be used on the ground as there is no cooling air wind. At the start , thermal anti ice is also switched off as far as possible so as not to deprive the engines of take- off power . If an engine fails during take-off, the lack of power due to the bleed air for thermal anti-ice could make the critical difference between “start with one engine” and “accident during take-off”. The same applies to the landing , as the pilots must always be prepared for a go - around .
In aircraft with piston engines , carburetor preheating is often used to prevent carburetor icing .
Accidents due to missing or insufficient de-icing
In chronological order:
- Air Florida Flight 90 , January 1982 - The crew neglected their checklists and used the reverse (reverse thrust) to pushback to exit the gate.
- Air Ontario Flight 1363 , March 1989 - The machine had not been de-iced because the engines could not be switched off due to a defective auxiliary power unit and the aircraft - a Fokker F28 - was not allowed to be de-iced with the engines running according to the manufacturer and airline's regulations in order not to pollute the cabin air with vapors.
- Scandinavian Airlines Flight 751 , December 1991 - Before take-off, the McDonnell Douglas MD-81 aircraft was insufficiently de-iced because a thick layer of clear ice had been overlooked on the top of the wing. After take off, the ice detached from the wings and was sucked in by the tail engines, which led to both engines failing one minute after take off. During the subsequent emergency landing in a field, the fuselage broke into three parts; all occupants survived the accident.
- USAir flight 405 , March 1992 - After take-off delays, the machine was not de-iced again, although this should have been done. The crew overlooked dangerous ice deposits on the wings and the tail unit and therefore did not consider a further de-icing necessary.
- American Eagle Flight 4184 , October 1994 - Freezing rain, which solidified to ice on the wings and worsened the aerodynamic properties of the wing, could not be removed from the wing trailing edges because no heating mats were installed here. As a result of the ice build-up and the disturbed flow around the profile, a reversal of the aileron torque occurred, which brought the aircraft into an uncontrolled position. The pilots could not bring the machine back under control.
- Air France flight 7775 , January 2007 - The combination of a steeper angle of attack than usual and hoarfrost on the wings that had not previously been de-iced caused a Fokker 100 of the Régional to tilt to the side several times when it took off at Pau-Pyrenees Airport , then lose height. The machine eventually rolled past the end of the runway at high speed.
- Saratov Airlines flight 703 - The crash of an Antonov An-148 of Russia's Saratov Airlines in Moscow Oblast died on 13 February 2018 in which all 71 passengers, is from the interstate aviation authority MAK erstursächlich on the icing of one or more pitot tubes with subsequent transmission of incorrect speed data fed back to the cockpit. The loss of airspeed led to the aircraft sagging quickly and causing it to crash.
Others
De-icing vehicles are (2008, 2015) labeled "enteisair" at Salzburg Airport.
Web links
- Insights: aircraft de-icing | Nuremberg Airport Nuremberg Airport , youtube.com, February 24, 2011, video (1:53)
-
About TKS Ice Protection Systems caviceprotection.com, CAV Ice Protection, manufacturer
- TKS Ice Protection System De-icing in Icing Wind Tunnel CAV Ice Protection, caviceprotection.com, youtube.com, October 22, 2014, video (0:30)
Individual evidence
- ↑ Investigation report no. 5X007-0 / 05 of the BFU - investigation of an exemplary incident due to deicing agent residues ( memento of the original from October 4, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Deicing agent ( Memento of the original from March 9, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , nice-services.aero, accessed January 16, 2011
- ↑ Wolfgang Rosenberger, Renate Wrbitzky, Manfred Elend, Sven Schuchardt: Investigations on the emission of organic compounds in the cabin air after the de-icing of commercial aircraft. In: Hazardous substances - cleanliness. Air . 74, No. 11/12, 2014, ISSN 0949-8036 , pp. 467-475.
- ↑ De-icing of aircraft with microwave patent DE19750198A1, filed November 13, 1997, published May 27, 1999, accessed January 20, 2019.
- ^ TKS - de-icing of aircraft in the air ultrablue-deicing.de, WITTIG Umweltchemie GmbH, Grafschaft-Ringen, accessed January 20, 2019.
- ↑ History caviceprotection.com, CAV Ice Protection System (2017), accessed January 20 of 2019.
- ↑ TKS system / TKS de-icing proz.com, Vova, March 9, 2003, accessed January 20, 2019.
- ↑ About TKS Ice Protection Systems caviceprotection.com, CAV Ice Protection System, New Century, Kansas (since 2013, before Salina, Kansas) and Consett, United Kingdom (since 1994, before Annefield Plain Industrial Park), 2018, accessed January 20 2019.
- ^ ASN Aircraft accident Fokker F28 Fellowship 1000 C-FONF Dryden Municipal Airport, ON (YHD). In: Aviation Safety Network . Retrieved April 13, 2011 .
- ↑ Investigation report on the accident of flight SK 751 October 20, 1993 (English)
- ↑ "enteisAir" at her job on January 24, 2015 at Salzburg Airport;) Karl Roth, fotocommunity.de, 2015, accessed January 20, 2019.
- ↑ Business with ski vacationers orf.at, January 20, 2019, accessed January 20, 2019.
