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Winter ops covers topics such as Types of Icing, Flight preparation, De / Anti-cing fluids and procedures, Hold Over Times, Braking Action, SNOWTAM Decodes, Altimeter Corrections and general precautions when operationing in winter time.
11 - Winter Precautions
It is important that flight crew are aware of the extra considerations needed when preparing and planning for flight.
Movement areas covered by slush, snow, water and ice create additional hazards. Typical reported incidents include vehicles colliding with parked aeroplanes, tugs sliding during pushback and aeroplanes encountering control difficulties during taxi.
THE CLEAN-AIRPLANE CONCEPT
The YouTube link above gives an interesting overview of the effects on Propellor driven aeroplanes / Icing induced stalls
Visible moisture (e.g., clouds, fog, rain, snow, sleet, or ice crystals) as well as ice, snow, slush, or standing water on the ramps, taxiways, or runways.
Snow, frost, slush, and other ice formations can cause undesirable air flow disturbances or can restrict air and fluid vents. Mechanical interference can also occur, resulting in restricted movement of flight controls, flap and slat operation, landing gear mechanisms, etc. Ice formation on turbine engine and carburettor air intakes can cause power loss. If the ice dislodges a turbine engine may ingest it, and engine damage or failure can occur. Ice on external instrumentation sensors (pitot/static ports, angle of attack sensors) can result in improper indications on cockpit instrumentation or improper operations of certain systems.
The presence of any of these contaminates MUST be removed prior to flight
The wings of an aeroplane are said to be “cold-soaked” when they contain very cold fuel as a result of having just landed after a flight at high altitude or from having been re-fuelled with very cold fuel. Whenever precipitation falls on a cold-soaked aeroplane when on the ground, clear icing may occur. Even in ambient temperatures between -2 C and +15 C (28 °F and 59 °F), ice or frost can form in the presence of visible moisture or high humidity if the aeroplane structure remains at 0 C (32 °F) or below. Clear ice is very difficult to be detected visually and may break loose during or after takeoff.
The following factors contribute to cold-soaking: temperature and quantity of fuel in fuel cells, type and location of fuel cells, length of time at high altitude flights, temperature of re-fuelled fuel and time since re-fuelling.
The presence of any of these contaminates MUST be removed prior to flight
The presence of any contaminates MUST be removed prior to flight
Normally applied hot under high pressure
This fluid 'shears' at 100kts therefore used on most jet aircraft
This fluid 'shears' at less than 100kts therefore used on smaller aircraft
This fluid provides a longer holdover time than type II and III fluids
Holdover time will have effectively run out when frozen deposits start to form/accumulate on treated aeroplane surfaces.
Due to their properties, Type I fluids form a thin liquid wetting film, which provides limited holdover time, especially in conditions of freezing precipitation. With this type of fluid no additional holdover time would be provided by increasing the concentration of the fluid in the fluid/water mixture.
With a one-step de-icing/anti-icing the holdover time begins at the start of the treatment and with a two-step de-icing/anti-icing at the start of the second step (anti-icing)
With this type of fluid additional holdover time will be provided by increasing the concentration of the fluid in the fluid/water mixture, with maximum holdover time available from undiluted fluid.
The table opposite is extracted from the FAA document ' HOLDOVER TIME GUIDELINES'. The times given give an indication as to the time frame of protection 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.
For a more detailed description of this procedure please consult your Operations Manual.
This pre-step process may be performed with various means (e.g., brooms, forced air, heat, heated water, and heated fluids with negative buffer freezing point). If the pre-step procedure is used, make sure that the subsequent de-icing process removes all frozen contamination including the contamination that may have formed on surfaces and or in cavities due to the pre-step process.
In some cases a full or complete de-icing is not necessary. When the presence of frost and/or ice is limited to localised areas on the surfaces of the aeroplane and no holdover time is likely to be required, only the contaminated areas will require treatment.
It is the responsibility of the De-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 Commander: “Local Area De-icing only. Holdover times do not apply”
Underwing frost and ice are usually caused by very cold fuel in the wing tanks.
Use a fluid/water mixture with a higher concentration of glycol than is usually required by the OAT to prevent re-freezing.
No holdover times apply to underwing treatments.
For light deposits of both wet and dry snow, similar procedures as for frost removal may be adopted.
Heavy accumulation of snow will always be difficult to remove from aeroplane surfaces and vast quantities of fluid will invariably be consumed in the attempt. Under these conditions, serious consideration should be given to removing the worst of the snow manually before attempting a normal de-icing procedure.
Non-metallic surfaces (e.g. composites) have a lower heat transfer than metallic surfaces. De-icing may take longer and more fluid may be needed.
aircraft manufacturer's instructions.
Fuselage, spray along the top centre-line and then outboard. Ensure that it is clear of snow, slush or ice in accordance with aircraft manufacturer's documentation. Hoarfrost may be allowed.
spray from the leading edge to the trailing edge. Do not spray from the rear. Start at the highest point of the surfaces and work to the lowest parts, i.e. on most aeroplanes start at the wing tip and work towards the wing root.
Nose/Radome Area and Flight Deck Windows - Type I fluid/water mixture or manual methods of removal (such as squeegees or brushes) are recommended.
When thickened fluids are used, avoid spraying near flight deck windows, as fluid can cause a severe loss of visibility during flight.
For Commercial Air transport flights an entry must be made in the aircraft technical log to record the process, even in the case of an interrupted or failed application (see EASA Part-M, AMC M.A.306(a), Section 3(vi)). EASA Part-M requires the time the de-icing commences, in the case of a one step process or the time at which the anti-icing process is commenced in a two step process, to be recorded in the aircraft technical log.
The commander should continually monitor the environmental situation after the performed de-icing/anti-icing treatment. Prior to take-off the commander should assess whether the applied holdover time is still appropriate and inspect the aircraft, to the extent possible, to ensure critical surfaces are clear of frozen contamination, especially any surfaces that have been de-iced/anti-iced. This check is normally done from inside the aircraft.