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Aircraft Ground De/Anti-Icing
- 1 Description
- 2 Effects
- 3 Defences
- 4 Typical Scenarios
- 5 Contributory Factors
- 6 Solutions
- 7 Additional Issues
- 8 Accident and Incident Reports
- 9 Related Articles
- 10 Further Reading
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 it begins flight with critical surfaces free from contamination by frozen or semi-frozen moisture (‘contaminant’). This is called the ‘clean aircraft’ concept.
Failure to remove contamination from an aircraft 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.
Intake duct deposits and engine blade deposits may detach and be ingested by the engine(s) during the subsequent application of high power settings for takeoff, with consequential adverse effects on engine operation, and possible flameout.
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 aircraft to determine if anti-icing is necessary.
- The correct application of appropriate 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.
- Detection of snow or slush within an engine nacelle may be difficult or even impossible using normal visual inspection; and removal of contaminants may be equally difficult. Therefore, every effort should be made to prevent the ingress of snow, rain, etc. by the use of engine inlet covers and plugs. 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 disappear inside the inlet of a turboprop engine to the extent that they are no longer visible, it will be evident that they have not been lost externally and that engineering assistance must be sought. Details of a fatal accident which highlighted the importance of this procedure can be seen at the accident report listed under 'Further Reading' below.
- In all respects, relevant aircraft manufacturer recommendations should be followed. Where appropriate guidance is not provided, 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.
- Failure to get airborne attributed to failure to ground de-ice beforehand.
- Loss of control shortly after an overweight take off in freezing precipitation and without ground de-icing of ice seen on the airframe prior to departure.
- Loss of control during flap retraction after take off attributed to failure to ground de-ice prior to take off.
- High speed Rejected Take Off (RTO) after a significant elevator split attributed to undetected ice in the elevator leading edge gap developed during the take off roll.
- Loss of Control shortly after take off after both engines failed, because ice was not removed from the wings before departure and was shed from the wings and ingested after take off.
- 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.
- 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. The best guides are those published by the specialist working groups of the Association of European Airlines (the European Focal Point for this subject, see below) and equivalent documentation produced for North America by the Society of Automotive Engineers (SAE).
- 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 Tables generated by SAE and AEA.
- 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 ground anti icing fluids has led to fluid residues accumulating in aerodynamically quiet areas of the external airframe structure and within the structure. When subsequently re-hydrated and then frozen in flight, control restrictions have been experienced on aircraft types such as the BAE 146/Avro RJ series and DC9/MD 80/90 series which have at least some unpowered flight controls. After a number of Serious Incident Reports, many Operators of the affected aircraft types have adapted their aircraft maintenance procedures to carry out appropriate inspections and residue removal.
Accident and Incident Reports
Accidents and Incidents resulting problems with de/anti-icing:
Failure to de/anti ice when facilities available
- 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.)
- CL60, Birmingham UK, 2002 (On 4 January 2002, a Challenger 604 operated by Epps Air Service, crashed on takeoff from Birmingham, UK, following loss of control due to airframe icing.)
Ground de/anti icing not available
- 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 stall and subsequent loss of control was attributable to 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 noted that the aircraft had been parked outside overnight and that conditions had favoured frost formation. The presence of a substantial quantity of cold-soaked fuel had favoured frost formation. The presence of a substantial quantity of cold-soaked fuel in the wing tanks overnight was also noted.)
Ground de/anti icing ineffective
- AT72, vicinity Tyumen Russian Federation, 2012 (On 2 April 2012, the crew of a UT Air ATR72-210 which had just taken off from Tyumen lost control of the aircraft and it crashed and caught fire killing or seriously injuring all occupants. The subsequent Investigation attributed the accident to the decision of the aircraft commander to take off without prior ground de icing when frozen deposits had accumulated on the airframe. However, a wide ranging systemic context for this was found, including ineffective regulatory requirements and a dysfunctional SMS at UT Air.)
- B463, en-route, South of Frankfurt Germany, 2005 (On 12 March 2005, a BAe-146-300 climbing out of Frankfurt experienced a loss of elevator control authority and an uncommanded descent at up to 4500 fpm whilst in a nose high pitch attde which was eventually arrested and subsequently attributed to the freezing of re-hydrated ground de/anti-ice fluid residues. The crew decided to continue to their originally-intended destination since it offered the prospect of more favourable weather conditions for landing. The aircraft later landed at Stuttgart after using elevator trim to control pitch attitude.)
- B732, vicinity Washington National DC USA, 1982 (On 13 January 1982, an Air Florida Boeing 737-200 took off in daylight from runway 36 at Washington National in moderate snow but then stalled before hitting a bridge and vehicles and continuing into the river below after just one minute of flight killing most of the occupants and some people on the ground. The accident was attributed entirely to a combination of the actions and inactions of the crew in relation to the prevailing adverse weather conditions and, crucially, to the failure to select engine anti ice on which led to over reading of actual engine thrust.)
- B733, Birmingham UK, 2009 (On the morning of 6 February 2009, a Boeing 737-300 being operated by bmibaby was departing from Birmingham for Edinburgh on a scheduled passenger flight and the crew had had the aircraft de-iced on the gate prior to departure. The stabiliser trim was not set at the usual time due to the ongoing de-icing procedure and the omission was not noticed after start because the crew became preoccupied with the flap setting. The aircraft started its takeoff run with the incorrect stabiliser trim setting and the First Officer, the designated PF, was subsequently unable to raise the aircraft nose at VR. The Captain then decided to reject the takeoff. The thrust levers were closed at 155 kts, considerably in excess of V1, and the aircraft stopped on the runway without further incident.)
- C208, Helsinki Finland, 2005 (On 31 January 2005, a Cessna 208 stalled and crashed on take off from Helsinki-Vantaa following failure to properly de-ice the aircraft.)
Unintended side effects of ground de/anti icing
- A320, en-route, Kalmar County Sweden, 2009 (On 2 March 2009, an Airbus A320-200 being operated by Wizz Air Hungary on a scheduled passenger flight from Stockholm Vasteras to Poznan was in the cruise at night when the flight crew detected an unfamiliar smell on the flight deck and decided to guard against possible incapacitation by donning their oxygen masks from time to time for the remainder of the flight. There was some evidence of the same effect in the passenger cabin. The flight was completed without further consequences and none of the 85 occupants was affected except temporarily.)
Ground de/anti ice fluid residue effect on flight controls
- ATP, Helsinki Finland, 2010 (On 11 January 2010, a British Aerospace ATP being operated by West Air Sweden on a cargo flight from Helsinki to Copenhagen with only the two operating flight crew on board at night could not be rotated for take off on runway 22R. The ensuing rejected take off in normal ground visibility was achieved within the available runway length and the aircraft was undamaged and returned to the apron.)
- AEA Recommendations for De-icing/Anti-icing on the Ground: The two regularly updated AEA Guides on the subject are:
- "Recommendations for De-Icing/Anti-Icing Aeroplanes on the Ground" and
- "Recommendations and Background Information for De-Icing/Anti-Icing Aeroplanes on the Ground"
- Transport Canada Guidelines for Aircraft Ground Icing Operations
- The NASA “Pilots Guide to Ground Icing” which reviews the problems caused by ground icing, when ground icing is likely to be encountered, the basics about aircraft de/anti-icing fluids and, in general, how to de-ice and anti-ice an aircraft. And also, especially for GA:
- The NASA “Pre Flight Icing Checklist”
- EASA Safety Information Notice (SIN) 2008-29 Ground De-/Anti-Icing of Aeroplanes; Intake/Fan-blade Icing and effects of fluid residues on flight controls
- EASA Safety Information Bulletin (SIB) 2010-26R1 Potential Performance Degradation of Anti-icing Fluids - Reduced Holdover Times
- FAA Advisory Circular Use of Liquid Water Equivalent System to Determine Holdover Times or Check Times for Anti-Icing Fluids