Chapter 10

Ice & Rain Protection

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SYSTEM DESCRIPTION

GENERAL

The airfoil ice-protection system supplies hot engine bleed air to the wing leading edge, forward strakes, ram air scoop and horizontal stabilizer leading edge.

Engine ice protection is self-contained within each engine nacelle and also uses engine bleed air. 

Engine bleed air also provides fuel heat. See Engine Fuel System, Chapter 14, for a description of this system.

Electrical heating elements protect three pilot tubes on the nose, rudder limiter pitot on the vertical stabilizer, stall angle of attack vanes, static ports, and the ram air temperature probe.

Electrical heat to the outer ply of the three windscreens provides anti-ice protection. Electrical heat to inner plys provides anti-fog capability for windshields, sliding windows, and eyebrow windows.

 

AIRFOIL ICE PROTECTION

 

Two airfoil anti-ice switches on the ice protection panel control airfoil ice protection on the STEAM panel and a single switch controls the airfoil anti-ice on the other panels. The two systems operate similarly with differences described below.

 

Airfoil ice protection only operates in flight. The pneumatic crossfeed valve must be open for each engine that supplies bleed air. Placing airfoil switch(es) ON opens a pressure regulator valve allowing air flow from the pneumatic crossfeed duct into the airfoil system. Minimum pressure for effective system operation is 20 psi as shown on the pneumatic pressure indicator.

 

OPERATING MODES

There are two modes of airfoil protection: wing and tail. Wing mode is automatically selected at system turn-on, as indicated by the WING ANTI-ICE ON annunciator light. In wing mode, hot air goes to the wings, forward strakes and the ram air scoop. 

 

In tail mode, electric power closes the wing valve and opens the tail valve to reroute air from the wings to the leading edge of the horizontal stabilizer.

 

When the tail mode activates, the WING ANTI-ICE ON light goes out and the blue TAIL DE-ICE ON light comes on. At the end of the 2 1/2 minute cycle, electric power is removed from the wind and tail valves. The wing valve opens and the tail valve closes (normal position for the valves), switching the system back to wing mode. Wing and tail mode annunciator lights indicate timer selection, not valve positions.

 

TWO-SWITCH SYSTEM - STEAM

 

There are 2 switches labeled LSYS and RSYS. Placing either switch to ON opens the pressure regulator valve. Each switch arms its respective augmentation valve for temperature control. Placing either airfoil switch to OFF disarms temperature control of the associated augmentation valve. When both switches are off, the pressure regulator valve closes, removing air from the system. 

 

The system remains in wing mode except for pilot selected periods of tail de-icing. Pushing the tail switch on the ice protection panel starts a timer and shifts the system to tail mode for 2 1/2 minutes.

 

SINGLE-SWITCH SYSTEM - COMBO & GLASS

 

System operation is similar to the two-switch system except that the pressure regulator will not open unless at least one pneumatic crossfeed is open. The respective pneumatic crossfeed valve must also be open to arm temperature control of the augmentation valve. If a crossfeed valve is closed, temperature control of the augmentation valve on that side is disabled. 

 

The single-switch system automatically cycles tail de-ice during continuous operation and at system shutdown. The system turns on in wing mode and a 15-minute timer starts. After 15 minutes of wing mode, tail mode is automatically selected. When the 2 1/2 minute tail mode cycle is complete, the system switches back to wing mode and the 15-minute timer restarts.

 

The single switch system also initiates a tail de-ice cycle when the airfoil switch is turned off. Crossfeed valves must remain open until the tail de-ice cycle is completed. The single switch system has a tail switch for manual selection of tail mode.

 

SYSTEM ABNORMAL INDICATIONS

 

PRESSURE ABNORMAL SENSING

 

The AIRFOIL ICE PROT PRESS ABNORMAL annunciator light operates in three different ways depending on airfoil anti-ice mode. In wing mode, the pressure abnormal light indicates low pressure in the wing ducts. In tail mode, the light indicates low pressure in the tail duct. When the system is shut down, the light indicates pressure still present in the wing duct. This indicates the pressure regulator is still open.

 

 

ENGINE ANTI-ICE

 

Engine anti-ice switches control anti-ice valves for each engine. Each switch controls three valves: two low pressure valves routing air to the inlet guide vanes and bullet, and one high pressure valve routing air to the forward edge of the cowling. Amber and blue annunciator lights indicate valve status. The ENG ANTI-ICE ON lights indicate that at least one anti-ice valve in the associated engine is open regardless of switch position. The ENG VALVE annunciator lights are disagreement lights. They come on if any valve remains closed when the switch is ON, or remains open with the switch OFF.

 

 

PITOT AND STATIC HEAT

 

Ice protection for pitot tubes (including rudder limiter), static ports, ram air temperature (RAT) probe, and stall angle of attack vanes is provided by electrical heating elements. Power to these elements is controlled by the meter selector and heat switch on the ice protection panel. With the switch in any position except OFF, all components are hated in flight. On the ground, all components are heated except the RAT probe.

 

In addition to controlling power use, the selector switch and meter to monitor electrical current flow to each component. A loss of electrical power to one of the following: captain's, first officer's. auxiliary, or rudder limiter pitot tubes will cause the PITOT/STALL HEATER OFF light to come on. 

 

 

WINDOW AND WINDSHIELD HEAT

 

Window heat is controlled by switches on the ice protection panel. One switch provides power for windshield anti-ice while the other controls the anti-fog system.

 

 

OVERWING HEATERS

 

Each overwing heater covers approximately 45 square feet of the upper wing surface just outboard of the overwing walkway. The heaters operate on the ground to maintain the heated upper surface between 40F (4C) and 85F (29C). 

 

Three annunciator lights on the Captain's instrument panel display system status. A WARM light illuminates when both heaters are 40F (4C) or above. When a fault is activated, the WARM light goes out and the associated L FAIL or R FAIL light will illuminate.

 

SYSTEM OPERATION

 

The WARM light should illuminate whenever both panels have been 40F or above for 40 seconds. This normally should occur within 10 minutes of AC and DC power being applied to the aircraft on the ground with no system faults detected. After landing, there is a one-minute system power start-up delay to prevent crew distraction during landing rollout or initial taxing when warm light illuminates.

 

When there is only one generator in operation, the Overwing Heater system is completely disabled. This is done automatically and requires no action from the crew.

 

 

Ice & Rain Protection

 

CONTROLS AND INDICATORS

 

ICE AND RAIN CONTROLS

 

 

LOCATION: Overhead Panel

 

AIRFOIL ANTI-ICE SWITCH

(TWO-SWITCH SYSTEM)

 

    OFF - Closes pressure regulator valve to stop air to airfoil anti-ice system. Deactivates temperature control of augmentation valve.

 

    ON - Opens pressure regulator and augmentation valve to provide heat to airfoil anti-ice system.

 

AIRFOIL ANTI-ICE SWITCH

(SINGLE-SWITCH SYSTEM)

 

    OFF -  initiates tail de-ice cycle. Closes pressure regulator valve after tail cycle complete to stop airfoil anti-ice system.

 

    ON - Opens pressure regulator valve if at least one pneumatic crossfeed is open. Opens augmentation valve if respective pneumatic crossfeed

              is open. Initiates 15-minute wing anti-ice timer.

 

HEATER CURRENT METER

 

Indicates current flow to the selected heater.

 

HEAT AND METER SELECTOR

 

Moving the selector from off heats pitot and rudder limiter pitit tubes, stall probes, static ports, and RAT probe. RAT probe is not heated on the ground.

 

TAIL DE-ICE SWITCH

 

Push to de-ice horizontal stabilizer. Closes wing and strake anti-ice shitoff valve and opens tail de-ice valve. After approximately 2 1/2 minutes, wing and strake anti-ice is restored.

 

 

ENGINE ANTI-ICE

 

 

LOCATION: Overhead Panel

 

ENGINE ANTI-ICE SWITCH

 

When on, two low pressure and one high pressure bleed air valves open to heat compressor inlet guide vanes, nose, and bullet.

 

 

WINDSHIELD ANTI-FOG AND ANTI-ICE

 

 

LOCATION: Overhead Panel

 

WINDSHIELD ANTI-FOG SWITCH

 

Controls anti-fog heating power to remove condensation on inside surface of windshields, clearview and eyebrow windows.

 

WINDSHIELD ANTI-ICE SWITCH

 

Controls anti-ice heating power to the three windhields.

 

 

OVERWING HEATER

 

 

LOCATION: Main Panel

 

L/R FAIL - Indicates a fault detected in respective system. Power is removed from affected heater and the WARM light is deactivated.

 

WARM - Indicates both heaters are operating between 40F and 85F.

 

 

ICE PROTECTION ANNUNCIATOR LIGHTS

 

 

L (R) ENG ANTI-ICE ON - Indicates engine anti-ice valve is open and engine anti-ice is on regardless of switch position.

 

WING ANTI-ICE ON - Indicates an airfoil anti-ice switch is on.

 

TAIL DE-ICE ON - Indicates de-icing heat has been selected for leading edge of horizontal stabilizer.

 

PITOT/STALL HEATER OFF - Indicates heat and meter selector switch is off, or in any other position indicates loss of electrical power to 

                                                       one or more pitot tubes or stall angle of attack vane heaters.

 

L (R) ICE PROTECT TEMP HIGH - Indicates air to crossfeed manifold is above normal operating temperature.

 

AIRFOIL ICE PROT PRESS ABNORM - Indicates low pressure to wing leading edge, forward strakes, horizontal stabilizer with airfoil 

                                                                        anti-ice switch on.

 

ICE PROTECT SUPPLY PRESS HI - Indicates duct pressure high downstream of ice protection pressure regulating valve.

 

L (R) ICE PROTECT TEMP LOW - Indicates air to pneumatic crossfeed manifold is below normal operating temperatures.

 

L (R) ENG VALVE - Indicates disagreement between engine anti-ice valves and switch positions. With switch on, at least one valve is closed.

                                    With switch off, at least one valve is full open. Normally will illuminate momentarily when turning on or off the engine 

                                     anti-ice.

 

 

SCHEMATICS