Ice & Rain Protection
Revised 28-Feb-2001
 
Back To Index

Ice protection is the prevention and removal of ice accumulation (anti-icing and de icing respectively) The pneumatic and electrical systems supply the required heat.

Engine bleed hot air for:
Wing anti-icing
Engine nose cowls and inlets and center engine inlet duct
The upper VHF antenna
Fuel filter de-icing (more under power plant)

Electrical power provides heat for:
Pitot tubes
Static ports
Temperature probe
Cockpit windows
Stall warning heater
Lavatory and galley drains

WING ANTI-ICING 
For wing anti-icing, bleed air from engines 1 and 3 flows through ducts in the leading edges of the wings and is the discharged overboard.
Air is passed through the leading edge slats, leading edge flaps (2 thru 5), fixed inboard wings above the leading edge flaps and the upper VHF antenna this is a mix of high and low pressure air. There is a automatic trip off system installed as a safety measure against a ruptured wing anti-ice duct in the pressurized area of the fuselage which would result in a rapid pressurization of the cabin (increase). If this occurs the wing anti-ice valves close automatically and the WING ANTI-ICE AUTO TRIP OFF light illuminates. (located on the flight engineers panel) There is a test switch installed to allow a check of the system before flight. Overheat protection is provided by temperature sensors located in the wing anti-ice ducting. When it gets too hot the DUCT OVERHEAT light illuminates. It's value is different depending whether you are in flight or on the ground. If you are on the ground is setting is less, and the anti-ice valves will close. In flight it has a higher value and the valves do not close. You can verify and locate the source of the overheat by looking at the DUCT TEMP indicator and using the anti-ice temp selector at the co pilots overhead panel. The wing anti-ice shutoff valves are overridden closed by pulling the fire handle. Valves are electrically operated.

ENGINE ANTI-ICING
Each engine supplies it's own anti-icing air and is separate and independent of the other two engine anti-ice systems. The engine nose cone, EPR port and inlet guide vanes are anti-iced by engine low pressure bleed air. The air is ducted through the left and right engine anti-ice valves, to the inlet guide vanes and nose cone, and vented into the engine intake.  When operating engine ant-ice you will see a drop in engine EPR. 
POD ENGINES. Nose cowls and CSD oil cooler scoops are anti-iced by engine high pressure bleed air ducted through the nose cowl anti-ice valve and mixed with ambient air. The mixed air is directed against the cowl and CSD scoop leading edges, exhausted overboard the a opening in the bottom of the engine cowl.
CENTER ENGINE. The inlet leading edge, part of the surface of the inlet duct, and the CSD oil cooler inlet are anti-iced by a combination of high and low pressure bleed air. Air is vented into the rear fuselage section and exhausted overboard through an opening in the left hand side. Bleed air is also used to anti-ice the vortex generators installed on the bottom of the inlet duct, this is vented into the engine intake.

COMPONENTS OF INTEREST
Thermostatic Modulating Valves. Control the volume of flow in relation to the temperature of the air, Higher the temperature the lower the flow.
Left Hand and Right Hand Engine Anti-Ice Valves. Left and right anti-ice valves on each engine control the bleed air flow through the guide vanes to the nose cone which also contains the EPR port. Valves are electrically operated.
Nose Cowl Anti-Ice Valves. Control high pressure bleed air flow to the pod engine nose cowls and center engine inlet duct. On the No2 engine, low pressure bleed air is also used for inlet duct anti-icing. A mixed air shutoff valve controls the flow of both high and low pressure bleed air to the inlet duct. The No 2 engine mixed air shutoff valve is overridden closed when the engine fire handle is pulled, it is electrically operated.

Window Heat
Cockpit windows, except No3 are electrically heated to provide anti-icing, defogging and impact resistance. Power to a electrically conductive coating within the laminated window is controlled by switches on the overhead panel above the co pilot Window heat is regulated by, The window heat controllers, Temperature sensors and thermal switches. 

Window Overheat Protection. An overheating window will not cause damage during flight. Due to the cooling airflow however when this is lost after landing damage could quickly occur if it was not for the protection system. At first overheating appears as small bubbles (like water droplets) this does not affect the structural integrity, but may cause problems with visibility. If the overheat condition persisted the window would splinter and crack. 
Don't assume the system overheat protection is working as I've hand a window fail. 
Windshield Anti-Icing. Anti-icing is provided for the No1 and No2 windows, control is through two switches on the control panel. marked High, Low, Off these select high or low voltage to control the rate of heating. If an overheat condition is detected a window overheat light will illuminate of the flight engineers door panel. It locks out the control and removes power from the respective No1 and opposite No2. It may be reset by cycling the switch to off.
Window Defogging No 4 and No5. These windows receive heat for defogging only and are powered when the switch is in the high or low position, they have no controller or overheat protection. Control of the heating is by a thermal switch on the No5 Window. Note the No3 window is not heated. Click here to see more about the windows.

Pitot - Static Heat
The left and right pitot probes, auxiliary pitot probe, left and right static ports, total air temperature probe (TAT) and the left and right elevator feel pitot probes are heated to prevent ice formation which would affect sensing accuracy. The heat is controlled by two switches on the co pilots overhead panel. It supplies 115V AC, When the left switch is placed on heating is applied to:
Captains pitot probe
Left static ports
TAT probe
Left elevator feel pitot probe
The right switch controls in the same manner as the left but operates
Co pilot pitot probe
Right static ports
Auxiliary pitot probe
Right elevator feel pitot probe
Static port heating has been deactivated on some 100's but is required on the 200.
Stall Warning Sensor Heat
The attitude sensor of the stall warning system is anti-iced by an integral electric heater. it is available when the airplane is on engine generators. When external or APU power is on the sync bus the heater is off except when checked by the test switch.
Rain Protection
Consists of electrically operated windscreen wipers operated by a switch on the overhead panel, these are install on both the No1 windows. The switch has the following positions Park, Off, Low, 1/2, 3/4 and High. There is a rain repellant system also for the No1 windows which is controlled by two switches, two time control valves and a fluid container. When a switch is pressed it opens a valve letting a fixed amount onto the windscreen on application takes appox 1/2 second. The system is little used and may be removed., There's an SB on this.

Back To Index