Ice and Frost Removing Methods

PRE-FLIGHT PREPARATIONS

Prior to flight the aircraft should be inspected to ensure it is free from deposits of frost, ice and snow and when necessary an approved de-icing fluid should be used.

The method of treatment will depend upon environmental conditions and whether the deposit is either ice, frost, snow or slush.

FROST DEPOSIT, METHOD OF TREATMENT

This is best removed using a product called Kilfrost ABC and can be either applied by spray or brush hand method, one application is usually sufficient and should be applied within 2 hours of flight.

Care should be exercised with glazed panels and new paintwork.

Alcohol based fluids are particularly prone to the ‘washing out’ of oils and greases from bearings resulting in an ingress of moisture which could subsequently freeze and jam controls.

ICE AND SNOW DEPOSIT, METHOD OF TREATMENT

Wet snow should be removed using a brush or ‘squeegee’ while light and dry snow can be removed using compressed air.

It is not advisable to use a hot blower owing to the possibility of wet snow freezing.

Moderate to heavy ice and residual frozen snow should be removed with a de-icing fluid and in some instances it may be necessary to spray the aircraft just prior to departure.

Care should also be exercised to prevent fluid from contaminating the aircraft windscreen and cabin windows.

COLD FLUID SPRAY METHOD OF DE-ICING

This is the simplest method, however in severe conditions several applications are sometimes necessary, making the operation less cost effective.

The fluid is normally sprayed by hand from a container either pressurised by air or fitted with a hand pump.

This method is used mainly in emergencies or at small airports.

HOT FLUID SPRAY METHOD OF DE-ICING

A static unit containing water and de-icing fluid is heated. This mixture is then pumped to a mobile unit which houses a tank, pump and a hydraulically operated boom mounted on a platform and several spray lances.

Hot fluid is pumped from the static unit to the insulated tank on the mobile unit, the proportions of water and fluid being adjusted to suit prevailing weather conditions.

Normal spray temperatures of 70'C and a pressure of 700 kN/mm2 are obtained.

This heat when transferred to the aircraft skin, breaks the ice bond and large areas of ice may be flushed away using the side of the nozzle. Fluid remaining on the aircraft skin being only slightly diluted is effective in preventing ice reforming.

HOT AIR METHOD

This consists of a hot air blower and is only suitable for frost deposits, care must be taken to ensure residual water is removed on completion of the defrosting.

Aircraft De-icing and Anti-icing

Aircraft de-icing and anti-icing systems are designed to remove or prevent the formation of ice on a limited area of the wings, tail and engine nacelles and would not normally be effective in removing deposits which have accumulated while the aircraft is stationary.
It is most important that all frozen deposits be removed from an aircraft before take-off otherwise its performance may be seriously affected.
This may be due to reduced lift and increased drag resulting from the disturbed airflow over the wing and tail surfaces, or it may be due to the extra weight of the frozen deposit over the whole aircraft.

In addition there could be freezing of moisture in controls, hinges and microswitches or the entry of ice into the engines.
Any measure taken to remove frozen deposits on the ground must prevent the possible re-freezing of liquid during the initial stages of flight when the flight de-icing or anti-icing systems are either not functioning or not yet fully effective.

There are two basic types of aircraft ground de-icing/anti-icing fluids:

• Type 1 unthickened fluids.
• Type 2 thickened fluids.

Type 1 fluids have a high glycol content (minimum 80%) and a relatively low viscosity, resistance to movement, except at very low temperatures. Their holdover time is relatively short. Holdover time is the length of time that the fluid will protect the wing from ice, frost and snow.

Type 2 fluids have a minimum glycol content of 50% and due to a thickening agent, enable the fluid to remain on the aircraft surfaces until take-off. These fluids have a good de-icing performance and significantly longer holdover times than Type 1 fluids, providing protection against refreezing and/or build up of snow.