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.

Lighting strick on Aircraft

Lightning is a discharge of electricity between highly charged clouds, or between a charged cloud and the ground.
If an aircraft is operating in the vicinity of such clouds, a discharge may strike the aircraft.
This may happen during flight or on the ground and can result in very high voltages and currents passing through the aircraft structure.

All separate parts of an aircraft are electrically bonded together to conduct a lightning strike away from areas where damage may hazard the aircraft, eg fuel tanks or flying controls.
Metallic wires or filaments within the composite structure, allowing for conductivity, may protect composite or non-metallic structures such as wing tips and nosecones.
The use of metallic wires or filaments within nosecones radomes or dielectric panels is a design feature that will not interfere with radio and radar efficiency and effect transmissions.
Lightning strikes may have two effects on an aircraft:
• Strike damage where the discharge enters the aircraft.
• Static discharge damage after the strike.

Strike damage is usually found at the wing tips, leading edges of wings and tail unit, and at the fuselage nose.
On some aircraft types, other areas may be more likely to be struck by lightning; Information on this should be obtained from the aircraft maintenance manual.Static discharge damage is usually found at wing tips, trailing edges and antenna.
Strike damage is usually in the form of small circular holes and pinholes in the exterior skin. These may be in clusters or spread out over a wide area.Burning or discoloration, blisters or holes may accompany them on radomes and cracks in glass fibre.Static discharge damage is usually in the form of local pitting and burning at trailing edges.

Effect of Ice formation on aircraft

During flight in certain conditions, ice may accumulate on the entire forward facing areas of the aircraft.
The accumulations of ice have the following effects on an aircraft:



•A decrease in lift due to a change in shape of the wing aerofoil section and loss of the streamline flow of air around the leading edges and top surfaces.

•An increase in drag for the same reasons that cause a loss of lift. The rough surface produced increases skin friction.

•Decreased propeller efficiency because of the change in blade shape. There is also the possibility of damage to the fuselage as a result of ice being flung off the propellers.

•There may be loss of control due to ice restricting or preventing movement of the control surfaces.

•An increase in weight causing loss of height. A change in distribution of the weight can cause a change in the trim of the aircraft and possibly a loss of stability.

•Blockage of pitot heads and static vents.

•Loss of vision through the forward facing cabin windows or windshields.

Water Distribution System

A main water distribution line runs from the tank into the space above the cabin ceiling,from there individual supply lines go to the galleys and toilets.

The distribution lines are usually of reinforced plastic tubing enclosed in an aluminium shroud.The outer shroud prevents leaking water dripping on to the cabin ceiling.The shroud conveys any leaking water to the lower fuselage area via drain tubes.The water then drains out of the fuselage via the drains.

Liquid Flush Toilets

Flush toilets are the most common type of toilet found in passenger aircraft.

Each toilet is completely self-contained, its waste collection tank being mounted directly below the toilet bowl.Each toilet unit is installed above the toilet compartment.

It consists of:

1. A seat. 

2. Cover and surround.

3. Toilet bowl

4. Tank top and flushing system 

5. Waste tank and outlet bowl

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  Below diagram shows an overview operational characteristics of an liquid flush type toilet.the ground connections and the ground flushing and cleaning method is very clearly shown in it. 
  
   

Removavble Toilets

The number and type of toilets fitted in an aircraft cabin varies according to the size and type of aircraft.

Large aircraft can accommodate several changes to the cabin area including additional toilets.

The removable or ‘portable toilet’ is the simplest type of aircraft toilet and is usually fitted in the smaller types of aircraft.

Often called an ‘Elsan’ toilet, it is simply a bin containing a quantity of disinfectant and deodorant.  A seat is fitted onto the top of the bin and when the toilet is installed in the aircraft it is covered with a decorative laminate.

At the end of a flight the toilet is removed from the aircraft and emptied.  After refilling with the correct amount of disinfectant and deodorant it is replaced in the aircraft.

Toilets of this type are normally secured by a quick release method of attachment such as pip pin fasteners.

Lifting Bags

Lifting bags or elevators are used to raise aircraft, which have crash landed and have collapsed undercarriages.

The lifting bags are placed under the aircraft and then inflated with air, raising the aircraft.  The aircraft may then be moved to a more suitable position (clear of the runway).

The lifting bags are made from a specially woven nylon fabric coated with a neoprene compound.  This fabric has good weathering qualities and can withstand contact with aircraft fuels and oils.

The lifting bag sections maintain a slab shape when inflated.  Each section is fitted with inflation/deflation valves, positioned to allow access from both sides.  The lower section is fitted with a ribbed plastic cover.  This prevents it from slipping during the lifting operation.  Harness attachment points are provided to allow the bags to be moved and positioned.

The use of these bags for raising damaged aircraft is a specialized task.  The object is to raise the aircraft with minimum of additional damage, using a minimum number of personnel.  The bags are designed to raise the aircraft only, not to move the aircraft.

To move the aircraft a ‘Jury’, temporary undercarriage may be used.