Rain, snow, and ice are transportation’s longtime enemies. Flying has added a new dimension particularly with respect to ice, under certain atmospheric conditions ice can build rapidly on airfoils and air-inlets. On days when there is visible moisture in the air, ice can form on aircraft leading edge surfaces at altitudes where freezing temperatures start. Water droplets in the air can be supercooled to below freezing without actually turning into ice unless they are disturbed in some manner, this unusual occurrence is partly due to the surface tension of the water droplet not allowing the droplet to expand and freeze. However, when aircraft surfaces disturb these droplets, they immediately turn to ice on the aircraft surfaces.
Ice or frost forming on aircraft creates two basic hazards:
- The resulting malformation of the airfoil that could decrease the amount of lift
- The additional weight and unequal formation of the ice that could cause unbalancing of the aircraft, making it hard to control
Enough ice to cause an unsafe flight condition can form in a very short period of time, thus some method of ice prevention or removal is necessary.
- Ice buildup increases drag and reduces lift
- It causes destructive vibration and hampers true instrument readings
- Control surfaces become unbalanced or frozen
- Fixed slots are filled and movable slots jammed
- Radio reception is hampered and engine performance is affected
- Ice, snow, and slush have a direct impact on the safety of flight. Not only because of degraded lift, reduced takeoff performance, and/ or manoeuvrability of the aircraft, but when chunks break off, they can also cause engine failures if ingested and structural damage.
- Fuselage of the aft-mounted engines are particularly susceptible to this foreign object damage (FOD) phenomenon. Wing-mounted engines are not excluded however ice can be present on any part of the aircraft and, when it breaks off, there is some probability that it could go into an engine. The worst case is that ice on the wing breaks off during takeoff due to the flexing of the wing and goes directly into the engine, leading to surge, vibration, and complete thrust loss.
- Light snow that is loose on the wing surfaces and the fuselage can also cause engine damage leading to surge, vibration, and thrust loss.
Ice can be detected visually, but most modern aircraft have one or more ice detector sensors that warn the flight crew of icing conditions if installed. An Annunciator light comes on to alert the flight crew. In some aircraft models, multiple ice detectors are used, and the ice detection system automatically turns on the WAI(Wing Anti Ice) Systems when icing is detected. Several ice prevention means to prevent or control ice formation are used in aircraft today:
- Heating surfaces with hot air
- Heating by electrical elements
- Breaking up ice formations, usually by inflatable boots
- Chemical application
Equipment is designed for anti-icing or for deicing. Anti-icing equipment is turned on before entering icing conditions and is designed to prevent ice from forming. A surface may be anti-iced by keeping it dry, by heating to a temperature that evaporates water upon impingement, or by heating the surface just enough to prevent freezing, maintaining it running wet. Deicing equipment is designed to remove ice after it begins to accumulate typically on the wings and stabilizer leading edges.
Either hot air or electrical heating protects critical areas of the aircraft as follows:
- In flight, hot air from the pneumatic system heats the three outboard slats (3-4-5) of each wing
- Air is supplied through one valve in each wing. the wing pushbutton on the anti ice panel controls the valves
- An independent air bleed from the high pressure compressor protects each engine nacelle from ice
- Air is supplied through a two-position (open and closed) valve that the flight crew controls with two pushbuttons, one for each engine
Probe and Window heating
- The aircraft uses electrical heating for anti-icing each windshield and defogging the cockpit side windows
- Two independent Window Heat Computers (WHC), one on each side
For more on Airbus 320 specifics, click here.