Cold Weather Operations SpiceJet- B737 The Company policy with respect to operations in ground icing conditions is “MAKE IT CLEAN AND KEEP IT CLEAN”. OM-A Chapter 15 : Ground De-Icing and AntiIcing Operations Introduction • Aircraft Icing is continuous threat in all regimes of flight. It is insidious hazard that particularly occurs during Take-Off, Climb, Descent, Holding, Approach and Landing. • Most incidents/accidents have taken place during: • Take-Off • Approach • Landing Effects of Aircraft Icing • A very small amount of roughness, in thickness as low as 0.36mm, caused by ice, snow or frost, disrupts the air flow over the wings and control surfaces of the aircraft. This can lead to: • • • • • • Severe Lift loss Increased Drag Increased Stall Speed Abnormal Roll and Pitch Characteristics Interruption to movement of aircraft control surfaces Significant addition to aircraft weight • Aircraft Takeoff performance is based upon clean surfaces. An airplane is designed using the predictable effects of airflow over clean wings. – Clean Airplane Concept “There is no such thing as an insignificant amount of ice on an aircraft ” De-Icing and Anti-Icing • If contamination checks determine that the aircraft has ice, frost or snow, the aircraft must be de-iced before takeoff. De-icing procedures ensure that all the contaminants are removed from aircraft surfaces. • If the outside conditions may lead to an accumulation of precipitation before Takeoff, the aircraft must be anti-iced. Anti-Icing procedures provide protection against the accumulation of contaminants. Icing Conditions Icing conditions exist when OAT (on the ground) or TAT (in flight) is 10°C or below and any of the following exist: • visible moisture (clouds, fog with visibility of one statute mile (1600m) or less, rain, snow, sleet, ice crystals, and so on) is present, Or • ice, snow, slush or standing water is present on the ramps, taxiways, or runways. CAUTION: Do not use engine or wing anti–ice when OAT (on the ground) or TAT (in flight) is above 10°C. Contamination Checks • Flight Crews and Ground Crews should conduct a Pre-Flight Aircraft Contamination Check. Any contamination found shall be removed by deicing treatment. • If anti-icing is also required, De-icing and Anti-icing may be accomplished using a one-step or a two-step method. • Contamination check shall include a visual inspection of complete aircraft paying close attention to the control surfaces. Contamination Checks • The PIC, the Maintenance Organization for base activities or the contracted agent shall determine whether aircraft de-/anti-icing are required. • The final decision rests with the PIC. His request will supersede the ground crew member’s judgment and may include additional instructions than already identified by the ground crew. • A PIC shall not commence take-off unless the external surfaces are clear of any deposit which might adversely affect the performance and/or controllability of the airplane except as permitted in the AFM. • For this reason, prior to departure, the PIC or an authorized person shall perform a contamination check to ensure that frost, snow, slush or ice adhering to any part of the aircraft which might adversely affect its performance is removed. SP.16.2 Exterior Inspection SP.16.3 Exterior Inspection Pre Takeoff Contamination Check • Pre take-off contamination check is a check of the critical surfaces for contamination. This check shall be performed when the applied holdover time has been exceeded. • This check must be completed as close to the take-off time (within 5 minutes before take-off) and normally from outside the aircraft. • If the check is unsatisfactory, de/anti-icing operation must be repeated. Types of De-Icing/Anti-Icing Fluids Type I fluids Type II Fluids Type IV Fluids Type III Fluids • Orange Colour • Yellowish Colour • Yellowish Colour • Green Colour • Low viscosity, • High viscosity (contains a • Used for slower • High viscosity (contains Unthickened thickening agent) a thickening agent) aircrafts with • Longest holdover time • Blown off before • Limited holdover time • Long holdover time • Blown off quickly • Blown off before rotation • Used mainly for de- at around 100 Kts due to rotation at around 100 icing shear stress Kts due to shear stress • Used for de-icing and anti- icing rotation speed less than 100 Kts • Used for de-icing and anti-icing Hold Over Time Performance of Anti-Icing Fluids is measured by Hold Over time. • Holdover time is the estimated time anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the protected surfaces of an aircraft, under (average) weather conditions mentioned in the guidelines for holdover time. • The start of the holdover time is from the beginning of the anti-icing treatment. • Hold Over Time is influenced by ambient temperature, Winds, Precipitation, Humidity, Aircraft Skin temperature and other factors. • Type I fluids have hold over time of 5 to 15 mins. whereas type II and IV fluids have hold over time of 30 to 80 mins. One Step and Two Step De-Icing/Anti-Icing Process • Some contaminants like frost can be removed and the surface protected from refreezing all at the same time using the same fluid and same mixture. This is called a ONE STEP PROCEDURE. This is generally performed with a heated unthickened fluid. • TWO STEP DE-ICING AND ANTI-ICING is a procedure performed whenever the contamination demands a de-icing process separately. After de-icing a separate over spray of anti-icing fluid shall be applied to protect the relevant surfaces thus providing maximum possible anti-ice capability. • With a one-step de-icing/anti-icing operation the HOT begins at the start of the operation and • With a two-step operation at the start of the final (anti-icing) step. • The ground personnel will advise the captain of the time when the process began so the holdover time can be properly monitored by flight crew. Exceeding the holdover time means that the anti-icing fluid has failed and lost its effectiveness, i.e. frozen precipitation is no longer absorbed by the diluted antiicing fluid, making the protection ineffective. The precipitation accumulates Clean aircraft concept not fulfilled Danger!!! When an aircraft has been anti-iced and returns due to the Hold over time expiration or the conditions warrant, the aircraft has to be de-iced again before receiving another coating of anti ice fluid. “Proper communication is as important as proper de-icing/anti-icing. There cannot be any doubt of the procedure, fluid used, hold over time, areas covered etc.” Hold Over Time Charts • Each Fluid has a documented Hold Over Time that is listed in a hold over time chart. • The HOT Charts give a range of HOT that could reasonably be expected under conditions of precipitation. However, due to the many variables that can influence holdover time, these times should not be considered as minimums or maximums as the actual time of protection may be extended or reduced, depending upon the particular conditions existing at the time. • The lower limit of the HOT indicates the estimated time of protection during moderate precipitation and • The upper limit indicates the estimated time of protection precipitation. during light • The responsibility for the application of these data remains with the user. Sample – Type I Fluid Hold Over Time Charts Sample – Type IV Fluid Hold Over Time Charts Factors Affecting Hold Over Time Outside Air Temperature • Although the freezing point of anti-icing fluid is lower than that of pure water, it can freeze. As the air temperature drops, anti-icing fluids become less able to absorb and melt the freezing precipitation. • In addition, as the temperature decreases, the fluids become more resistant to shearing off the aircraft during the take-off roll. • It can get so cold that a fluid cannot be used safely on an aircraft either because it cannot afford any protection or because it may substantially interfere with the airflow over the lifting surfaces. A Lowest Operational Use Temperature (LOUT) is specified for every fluid. When the temperature is below the LOUT, that fluid should not be used. Precipitation Type and Intensity • Anti-icing fluids work by absorbing and melting precipitation. Conversely, precipitation dilutes the anti-icing fluid. The more dilute the anti-icing fluid becomes, the less protection it affords. Ultimately, the anti-icing fluid will fail. The more moisture present, the shorter the holdover time. • Both the type of precipitation and its intensity are key factors in determining HOT. Fluid Type and Concentration • • Type I must always be applied heated and diluted. It is essentially a de-icing fluid that can also be used for anti-icing in a two-step process. As the least viscous (thinnest) of fluids, it has the shortest HOTs. Types II, III and IV may be applied unheated or heated, full strength or diluted. The thickening agents added to these fluids to increase viscosity, and correspond to longer HOTs. In general, the more dilute the Type II, III or IV fluid, the shorter the holdover time. “No person may takeoff an aircraft when frost is adhering to wings, control surfaces, propellers, engine inlets or other critical surfaces of the aircraft.” This regulation is based on the clean aircraft concept which requires that critical aircraft surfaces are clean and any contamination not adhering to critical surfaces will blow off early in the takeoff roll. Considerations For De-Icing/ Anti-Icing • The De-/anti-icing process must be continuous and as short as possible to preserve holdover time. • The flight crew should ensure that the de-/anti-icing procedures are performed at the latest possible time before take-off in order to utilize maximum holdover time. • If holdover times for the prevailing weather conditions are not available, a take-off must not be performed. • The PIC may deviate from this rule, if the limiting weather conditions are no longer existing (i.e. weather information not yet updated). Removal Of Local Area Contamination • When no precipitation is falling or expected, a “local area” de-icing may be carried out under the following or similar conditions. • In some cases a full or complete de-icing is not necessary. When the presence of frost and/or ice is limited to localized areas on the surfaces of the airplane and no holdover time is likely to be required, only the contaminated areas will require treatment. • This type of contamination will generally be found on the wing and/or stabilizer leading edges or in patches on the wing and/or stabilizer upper surfaces. • Spray the affected area(s) with a heated fluid/water mixture suitable for a one-step procedure. Then spray the same area(s) on the other side of the airplane. • Both sides of the airplane must be treated identically (same areas, same amount and type of fluid, same mixture strength), even if the contamination is only present on one side. • A trained and qualified person must check that both the treatment was performed symmetrically and that all contamination has been removed. • It is the responsibility of the De-/anti-icing Operator to ensure that the treatment is performed symmetrically and that on completion all frozen deposits have been removed. • After this check has confirmed that the treated areas are clean, the following statement shall be given to the PIC: “Local Area De-icing only. Holdover times do not apply”. Supplementary Procedures Probe Heat Switches must be ON Engine Start Procedure Engine Anti Ice must be selected ON immediately after both Engines are started and remain on during all ground Operations when icing conditions exit or are anticipated An increase in control forces can be expected at low temperatures during Flight control Check Aircraft Configuration during De-Icing /AntiIcing After Landing Procedure Cold Temperature Altitude Corrections SP.16.12 Cold Temperature Altitude Corrections SP.16.13 Cold Temperature Altitude Corrections SP.16.14 Additional Considerations • For Approach to Land, Pilots must account for any Landing Weight penalties that may exist for ice on the aircraft structure or for ice on nonheated tail components. Additional Considerations • Since conditions can change rapidly, pilots should also be aware of the runway condition and weather changes since the last runway surface condition report. • Pilots should check the performance data to ensure the runway length is adequate for the conditions. PIC Responsibilities (a) The PIC is responsible for effective de/anti-icing. His request for treatment will supersede ground crew member’s decision and may also include additional instructions than already identified by the ground crew; (b) Establish that any aircraft surfaces that have been de-/anti-iced prior to arrival at the aircraft have remained free of frozen/freezing contamination; (c) Ensure that critical aircraft surfaces remain free of frost, ice, slush and snow until the start of take-off; (d) If at any time prior to take-off, the PIC requires confirmation of the ice-free state of the aircraft, he must carry out or order a visual inspection or return to the ramp; (e) Whenever de-icing/anti-icing has been performed on the aircraft, the PIC must make an appropriate entry in the Aircraft Technical Log showing the start time, stop time, type of Fluid, mix ratio and sign it. (f) Prohibition from operating an aircraft from any airport when conditions conducive to ground aircraft icing exist. (g) Before commencing de-/anti-icing treatment, the PIC shall ensure that both Cabin crew and passengers are advised.
