Aircraft Ground De/Anti Icing procedures serve three purposes: removal of any frozen or semi frozen moisture from critical external surfaces of an aircraft on the ground prior to flight; and/or, protection of those surfaces from the effects of such contaminant for the period between treatment and becoming airborne; and/or, removal of any frozen or semi frozen moisture from engine intakes and fan blades and protection of external surfaces from subsequent contamination prior to takeoff. It should be noted that fan blade ice which may be accumulated after the pre-start visual inspection, including whilst the engines are running at low thrust prior to take off, is removed by following prescribed engine handling procedures.
First of all, the aircraft must be inspected for signs of contaminant already adhering to surfaces and where found on surfaces which must be free of contaminant, it must be removed using a suitable ground de-icing fluid.
Secondly, the prevailing weather conditions must be assessed. If further adherence of contaminant to the airframe surfaces is currently occurring or anticipated prior to the time at which it is expected that the aircraft will get airborne, then a suitable ground anti-icing fluid should be applied. In both cases, the time after the start of fluid treatment from which protection is provided by the fluids applied depends upon the prevailing conditions. The fluids are designed to shear off the aircraft surfaces to which they have been applied no later than the point at which the aircraft becomes airborne. This means that the ground application of fluids has no effect upon the risks which arise from the accretion of frozen deposits on the aircraft at any time after take off.
The aerodynamic effectiveness of an airframe requires that an aircraft becomes airborne with critical airframe surfaces free from contamination by frozen or semi-frozen deposits (‘contaminant’). This is called the ‘clean aircraft’ concept.
Failure to remove contamination from an airframe and/or to protect it from acquiring further contamination before it becomes airborne may result in sudden loss of control at or shortly after take off. In the case of aircraft with rear mounted engines, any ice on the inner wings of an aircraft at take off may be shed and ingested into the engines causing a partial or total loss of thrust.
In respect of engines, frozen deposits within the intakes including on the fan blades of jet engines may detach and be ingested by the same engine(s) during the subsequent application of take off power, with the attendant risk of adverse effects on engine performance during the potentially critical stage of initial climb, including the possibility of engine flameout.
- The difficulties of reliably ascertaining the contaminant status of the aircraft because of a lack of suitable access equipment and/or the absence of adequate external lighting at night.
- The need for flight crews to rely upon assurances from other persons that their aircraft is free of contaminant after treatment at 'off-gate' or ‘remote’ sites.
- Deterioration of the properties of de/anti-icing fluids due to failure to store them correctly.
- Inadequate de/anti icing service at smaller airports which do not regularly experience icing conditions. This may be because of the use of ground staff ‘multi tasking’ and their consequent infrequent application of the tasks for which they have been trained.
- Complacency by flight crews not routinely encountering conditions requiring ground de/anti icing in respect of frost on critical swept wing surfaces.
To protect against loss of control, the following precautions should be taken prior to flight in weather conditions which are or have recently been conducive to ice accretion:
- A thorough inspection of all the airframe critical surfaces to establish if any existing contaminant is present; the prevailing surface temperature of the aircraft skin is as important as the prevailing Outside Air Temperature (OAT).
- A consideration of the weather conditions which prevail - and are likely to prevail - after the start of any treatment of ice already on an airframe to determine if anti-icing is necessary.
- The correct application of appropriate airframe De-Icing Fluids and/or Anti-Icing Fluids and the correct use of the De/Anti-Icing Code to help prevent any mis-understandings.
- The determination and monitoring of the applicable Holdover Time by the flight crew so that take off is not attempted if it cannot be completed within that time. It is important to note that the applicable Holdover Time may change if prevailing conditions change.
- Not taking off if there is no applicable holdover time for the weather conditions which have prevailed at any time since the commencement of ground anti-icing (this applies for Heavy Snow, Hail (defined as ice pieces between 5 and 50mm diameter), Snow or Ice Pellets (defined as hail of less than 5mm in diameter) and Moderate or Heavy Freezing Rain.
- Care to reduce holdover times if the effect of either jet blast or high wind speeds indicate that this would be prudent.
- If an turbine-engine aircraft has been exposed to frozen deposits whilst parked on the ground prior to intended fight without having blanks/covers fitted to engine intakes, detection of snow or slush within the engine is likely to be impossible using normal visual inspection and removal of contaminants equally difficult so qualified engineering assistance should be sought. For this reason, every effort should be made to prevent the ingress of snow, rain, etc. by the use of engine inlet covers and blanks. However, it is vital that these are both properly secured and that their fitment is recorded in the Aircraft Technical Log. Should they become dislodged and cannot be located externally or visibly inside the inlet of a turboprop engine, they may be out of sight within the engine and engineering assistance must be sought.
- In all respects, relevant aircraft manufacturer recommendations should be followed. Where appropriate guidance is not available, aircraft operators should liaise with manufacturers, regulators and other qualified entities to obtain advice which will enable them to develop suitable procedures. Such procedures should be described in Operations Manuals.
- All flight crew and all other persons involved in the inspection of aircraft for contaminants and the application of ground de/anti icing fluids should receive initial and recurrent training on the subject.
- Every AOM or POH should contain comprehensive and up to date information for flight crew on ground de/anti icing, with special attention being given to incorporation of the latest Holdover Time (HOT) Tables.
- Effective Quality Control procedures should be in place to ensure that proper procedures for the delivery of ground de/anti icing by service providers exist and are followed. In addition, Aircraft operators should ensure that Quality Assurance procedures cover Ground De/Anti Icing.
- The De/Anti-Icing Code should be used at all times to communicate and record the details of the aircraft treatment carried out to avoid any mis-understandings.
- Regarding engine intake de/anti-icing, operators are recommended to follow the advice contained in EASA SIN 2008-29.
Use of thickened Type 2 and Type 4 ground de/anti icing fluids has sometimes resulted in fluid residues accumulating in aerodynamically quiet areas of the external airframe structure, in particular between in the gap between the leading edge of the elevator and the horizontal stabiliser and also in the gap between the leading edge of the ailerons and the wing structure. When subsequently this residue is subsequently re-hydrated and then exposed to sub zero temperatures in flight, it freezes and can then result in primary flight control restrictions on aircraft types such as the BAE 146/Avro RJ series and the DC9/MD 80/90 series which have at least some unpowered flight controls. After a number of Serious Incident Reports, many Operators of affected aircraft types have adapted their aircraft maintenance procedures to carry out appropriate inspections and residue removal when these fluids have been applied.
During winter operations, the aircraft brakes and the open wheel well/bay may be exposed to alkali-organic salt runway de/anti-icing substances during taxi, take-off and landing. A slush mixture of snow and alkali-organic salt de/anti-icing substances could freeze onto the landing gear and the interior of the wheel well/bays. If, after landing gear retraction, such frozen deposits begin to melt, the resulting liquid is liable to flow into the core of the brake unit, If the brake discs are made of carbon rather than steel, the presence of the alkali-organic salt creates a catalytic condition which lowers the oxidation temperature of the carbon and leads to structural deterioration of the carbon disc material so that efficiency and ultimately the service life of the brake unit is reduced. Aircraft Operators need to consider whether any special inspections are appropriate in the light of their operations.
Accidents and Incidents resulting problems with de/anti-icing:
- CL60, Birmingham UK, 2002 (On 4 January 2002, the crew of US-operated Bombardier Challenger lost control of their aircraft shortly after taking off from Birmingham and after one wing touched the ground, it rolled inverted, crashed and caught fire within the airport perimeter and all five occupants died. The Investigation found that the cause of the accident was failure to remove frost from the wings which reduced the wing stall angle of attack below that at which the stall protection system was effective. It was considered that the combined effects of non-prescription drug, jet lag and fatigue may have impaired crew performance)
- AT72, vicinity Manchester UK, 2016 (On 4 March 2015, the flight crew of an ATR72 decided to depart from Manchester without prior ground de/anti icing treatment judging it unnecessary despite the presence of frozen deposits on the airframe and from rotation onwards found that manual forward control column input beyond trim capability was necessary to maintain controlled flight. The aircraft was subsequently diverted. The Investigation found that the problem had been attributable to ice contamination on the upper surface of the horizontal tailplane. It was considered that the awareness of both pilots of the risk of airframe icing had been inadequate)
- C208, Helsinki Finland, 2005 (On 31 January 2005, the pilot of a Cessna 208 which had just taken off from Helsinki lost control of their aircraft as the flaps were retracted and the aircraft stalled, rolled to the right and crashed within the airport perimeter. The Investigation found that the take off had been made without prior airframe de/anti icing and that accumulated ice and snow on the upper wing surfaces had led to airflow separation and the stall, a condition which the pilot had failed to recognise or respond appropriately to for undetermined reasons)
- CL60, Montrose USA, 2004 (On 28 November 2004, the crew of a Bombardier Challenger 601 lost control of their aircraft soon after getting airborne from Montrose and it crashed and caught fire killing three occupants and seriously injuring the other three. The Investigation found that the loss of control had been the result of a stall caused by frozen deposits on the upper wing surfaces after the crew had failed to ensure that the wings were clean or utilise the available ground de/anti ice service. It was concluded that the pilots' lack of experience of winter weather operations had contributed to their actions/inactions)
- AT72, vicinity Tyumen Russian Federation, 2012 (On 2 April 2012, the crew of an ATR72-200 which had just taken off from Tyumen lost control of their aircraft when it stalled after the flaps were retracted and did not recover before it crashed and caught fire killing or seriously injuring all occupants. The Investigation found that the Captain knew that frozen deposits had accumulated on the airframe but appeared to have been unaware of the danger of not having the airframe de-iced. It was also found that the crew had not recognised the stall when it occurred and had overpowered the stick pusher and pitched up)
- JS41, en-route, North West of Aberdeen UK, 2008 (On 9 April 2008, a BAe Jetstream 41 departed Aberdeen in snow and freezing conditions after the Captain had elected not to have the airframe de/anti iced having noted had noted the delay this would incur. During the climb in IMC, pitch control became problematic and an emergency was declared. Full control was subsequently regained in warmer air. The Investigation concluded that it was highly likely that prior to take off, slush and/or ice had been present on the horizontal tail surfaces and that, as the aircraft entered colder air at altitude, this contamination had restricted the mechanical pitch control)
- PRM1, vicinity Annemasse France, 2013 (On 4 March 2013, a Beechcraft Premier 1A stalled and crashed soon after take off from Annemasse. The Investigation concluded that the loss of control was attributable to taking off with frozen deposits on the wings which the professional pilot flying the privately-operated aircraft had either not been aware of or had considered insignificant. It was found that the aircraft had been parked outside overnight and that overnight conditions, particularly the presence of a substantial quantity of cold-soaked fuel, had been conducive to the formation of frost and that no airframe de/anti icing facilities had been available at Annemasse)
- C208, vicinity Pelee Island Canada, 2004 (On 17 January, 2004 a Cessna 208 Caravan operated by Georgian Express, took off from Pellee Island, Ontario, Canada, at a weight significantly greater than maximum permitted and with ice visible on the airframe. Shortly after take off, the pilot lost control of the aircraft and it crashed into a frozen lake)
- MD81, vicinity Stockholm Sweden, 1991 (On 27 December 1991, an MD-81 took off after airframe ground de/anti icing treatment but soon afterwards both engines began surging and both then failed. A successful crash landing was achieved after the aircraft emerged from cloud approximately 900 feet above terrain and only eight of the 129 occupants were seriously injured. The Investigation found that undetected clear ice on the upper wing surfaces had been ingested into both engines and caused damage which initiated the surging. Without training in the identification and elimination of engine surging, the pilots had not taken corrective action and so both engines had failed)
- ATP, Helsinki Finland, 2010 (On 11 January 2010, a British Aerospace ATP crew attempting to take off from Helsinki after a two-step airframe de/anti icing treatment (Type 2 and Type 4 fluids) were unable to rotate and the take off was successfully rejected from above V1. The Investigation found that thickened de/anti ice fluid residues had frozen in the gap between the leading edge of the elevator and the horizontal stabiliser and that there had been many other similarly-caused occurrences to aircraft without powered flying controls. There was concern that use of such thickened de/anti ice fluids was not directly covered by safety regulation)
- B463, en-route, South of Frankfurt Germany, 2005 (On 12 March 2005, the crew of a BAe 146-300 climbing out of Frankfurt lost elevator control authority and an un-commanded descent at up to 4500 fpm in a nose high pitch attitude occurred before descent was arrested and control regained. After landing using elevator trim to control pitch, significant amounts of de/anti-icing fluid residues were found frozen in the elevator/stabilizer and aileron/rudder gaps. The Investigation confirmed that an accumulation of hygroscopic polymer residues from successive applications of thickened de/anti ice fluid had expanded by re-hydration and then expanded further by freezing thus obstructing the flight controls)
- D328, Isle of Man, 2005 (On 28 November 2005, a Dornier 328 being operated by EuroManx on a scheduled passenger service departing from Isle of Man for an unspecified destination was unable to rotate at the speed calculated as applicable and the take off was successfully rejected. The Investigation found that the crew were unaware of the AFM 'Normal Procedures' requirement to use take off speeds after application of thickened de ice fluids which are typically around 20 knots higher than normal speeds)
- DH8A, Ottawa Canada, 2003 (On 04 November 2003, the crew of a de Havilland DHC-8-100 which had been de/anti iced detected a pitch control restriction as rotation was attempted during take off from Ottawa and successfully rejected the take off from above V1. The Investigation concluded that the restriction was likely to have been the result of a remnant of clear ice migrating into the gap between one of the elevators and its shroud when the elevator was moved trailing edge up during control checks and observed that detection of such clear ice remnants on a critical surface wet with de-icing fluid was difficult)
- A320, en-route, Kalmar County Sweden, 2009 (On 2 March 2009, communication difficulties and inadequate operator procedures led to an Airbus A320-200 being de-iced inappropriately prior to departure from Vasteras and fumes entered the air conditioning system via the APU. Although steps were then taken before departure in an attempt to clear the contamination, it returned once airborne. The flight crew decided to don their oxygen masks and complete the flight to Poznan. Similar fumes in the passenger cabin led to only temporary effects which were alleviated by the use of therapeutic oxygen. The Investigation concluded that no health risks arose from exposure to the fumes involved)
- SAE AS6286, Training and Qualification Program for Deicing/Anti-Icing of Aircraft on the Ground
- Although the AEA ceased to exist in 2016, the most recent of their AEA Recommendations for De-icing/Anti-icing on the Ground publications still contain some pertinent information. Readers are cautioned to validate the recommendations of these guidebooks using more current information sources.
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