Ice and Rain Protection

Table of Contents:

Normal Operations:

  • General
  • Nacelle Anti-Ice
  • Wing Anti-Ice
  • Rain Repellent


Alternate Operations:

  • Arcing/Delaminated/Shattered or Cracked Window
  • Window 1 Overheat Light Illuminated in Flight
  • Nacelle Valve Open Light Fails to Illuminate
  • Nacelle Valve Open Light Fails to Extinguish
  • Nacelle TAI Valve Light Remains Illuminated or Fails to Illuminate After Wing Anti-Ice Switched On
  • Wing Anti-Ice Valve Light Remains Illuminated or Fails to Illuminate After Wing Anti-Ice Switched Off
  • Probe Heat Power Off Light Illuminated
  • Stator Valve Open Light Fails to Illuminate
  • Stator Valve Open Light Fails to Extinguish


Controls and Indicators:

  • Wing and Nacelle Anti-Ice
  • Low Ni Light
  • Window Heat
  • Probe Heaters
  • Rain Repellent, Windshield Washer and Wiper


Schematics:

  • NAI

Supplementary Information:

  • Engine Anti-Ice
  • Wing Anti-Ice
  • Window Heat

Limitations.




Normal Operations

General:
Operation of the NACELLE ANTI-ICE and WING ANTI-ICE systems impose a heavy demand on the engine pneumatic air supply.
To assure adequate anti-icing during low thrust operation (descent or holding) the pneumatic duct pressure should be maintained at or above 15psig.

Duct pressure may be increase by using either of the following:
- Increase thrust to obtain higher pressure and flow from the low stage bleed.
- Reduce air condition bleed to TWO PACK OPERATION.

During holding, if any NACELLE VALVE OPEN light extinguishes, reduce thrust on two engines to 50% N1 RPM above 10,000 feet or 45% N1 below 10,000 feet and advance thrust on other engines to maintain desired flight path.
- The engines operated at 50% N1 will be afforded ice protection from hot bleed air from the high stage (HIGH STAGE light illuminated).  The engines operated at the higher RPM will receive sufficient hot bleed air from the low stage.

When penetrating or operating in Icing Conditions inflight, maintain a minimum of 50% N1 RPM at 10,000 feet and above, and 45% N1 below 10,000 feet except as required for landing.
Note:  The above minimum thrust settings must also be maintained when operating in clouds at temperatures below -40 C SAT with nacelle anti-ice ON or OFF to prevent ice forming internally in the engine.  Under these conditions, visible moisture will normally be in the form of ice crystals (cirrus clouds) which do not adhere to the nacelle or other airplane surfaces.
If the LOW N1 caution light illuminates, increase N1 RPM until light extinguishes.

Icing conditions exist when:
The OAT on the ground and for take off or TAT inflight is 10 C or below, and visible moisture in any form is present (such as clouds, fog with visibility of one mile or less, rain, snow, sleet and ice crystals).

Icing Conditions also exist when:
The OAT on the ground and for takeoff is 10 C or below when operating on ramps, taxiways or runways where surface snow, ice, standing water or slush may be ingested by the engines or freeze on engines, nacelles or engine sensor probes.

Caution:  The autothrottle should be monitored closely or turned off during icing conditions as it does not provide minimum N1 for wing and/or Nacelle Anti-Ice protection.
The autothrottle should be off priot to descent into icing conditions.


Nacelle Anti-Ice:
Nacelle anti-ice must be ON during all ground and flight operations when icing conditions exist or are anticipated, except during climb and cruise when the temperature is below -40 C CAT.
Nacelle anti-ice must be ON prior to and during descent in all icing conditions, including temperatures below -40 C SAT.

Caution:  Do not operate nacelle anti-ice when the TAT is above 10 C.

Erratic EPR indications or abnormal EPR relative to N1 may be an indication of engine icing.

When engine anti-ice is required:
Engine Ignitiion Switches (SYS 1 or SYS 2)...... FLT START
Nacelle Anti-Ice switches..... ON
Check Nacelle Valve Open lights illuminated.
When engine operation stabilized and flight conditions permit:
Engine Ignition switches ...... OFF
When engine anti-ice no longer required:
Nacelle Anti-Ice Switches ..... OFF
Check Nacelle Valve Open and Stator Valve Open lights extinguish.


Wing Anti-Ice:
Operate wing anti-ice system by turning it on following an icing encounter.
Caution:  Do not operate WAI when the TAT is above 10 C.
Wing Anti-Ice Switch..... ON
Check wing anti-ice VALVE lights illuminate, then extinguish.
Note:  If icing conditions exist, turn wing anti-icing on after retracting leading edge flaps or prior to extending leading edge flaps.  Anti-icing of leading edge flaps is not effective with flaps extended.


Rain Repellent:  Mainly deactivated - but information included here for information purposes.
Rain repellent may be used any time rain intensity requires the use of windshield wipers.  Apply repellent to one windshield at a time allowing fluid to spread and visibility to improve before applying to the other windshield.
Note:  Do not use rain repellent on a dry windshield and if inadvertently applied, do not use windshield wipers unless the windshield washer is activated first.


Alternate Operations

Arcing/Delaminated/Shattered or Cracked Window
Window 1 Overheat Light Illuminated in Flight
Nacelle Valve Open Light Fails to Illuminate
Nacelle Valve Open Light Fails to Extinguish
Nacelle TAI Valve Light Remains Illuminated or Fails to Illuminate After Wing Anti-Ice Switched On
Wing Anti-Ice Valve Light Remains Illuminated or Fails to Illuminate After Wing Anti-Ice Switched Off
Probe Heat Power Off Light Illuminated
Stator Valve Open Light Fails to Illuminate
Stator Valve Open Light Fails to Extinguish


Controls and Indicators


Wing and Nacelle Anti-Ice:

Wing Anti-Ice Switch:
ON - Opens both valves and directs engine bleed air to wing leading edge areas.  Operative only in flight.
OFF - Closes both valves.
GRD TEST - Used for checking valve operation on ground.  The valves automatically close before the wing leading edge temperature becomes excessive.  Operative only on ground.


Low N1 Light:

Flashes if any Nacelle Anti-Ice is ON and N1 is less than 50% above 10,000 feet or 45% below 10,000 feet.  The light is inhibited on the ground and in the air with landing flaps positioned.


Window Heat:


Window Heat Switch
ON - Window heat controller applies heat to window as required for anti-icing and defogging.
OFF - Window heat not in use.  Resets trip circuits if an overheat has occurred.
OVRD - A reduced constant heat applied to window for anti-fogging only.


Probe Heaters:
Probe heat meter - Indicates current used to heat probes selected by probe heat meter switch.
Probe heat switch: 
On - Applies heat to Pitot-Static, Auxiliary and Temperature probe.
PITOT ONLY - Same as above except no heat to temperature probe.

Note:  With probe heat ON, TAT and SAT indicators will not give accurate indications on the ground and flags normally appear.



Rain Repellent, Windshield Washer and Wiper:


Windshield Wiper Switch:

As required during rain or with water fluid applied.

Limitation: Never use Windshield Wipers on a dry windshield
Repellant function removed/disabled on most aircraft

Schematics


NAI - See AOM

Supplementary Information


Engine Anti-Ice - JT9D Engines:

The engine inlet cowl and Pt2 EPR probe are anti-iced by engine bleed air from the pneumatic system through the nacelle anti-ice valve which limits the maximum pressure of the bleed air.  With low duct pressure, NAI valves close and NACELLE VALVE OPEN lights extinguish.  If a valve malfunction allows higher than normal pressure air into a NAI system, the NAC TAI VALVE light illuminates.
On -7R4G2 powered airplanes, the Pt2 probe is electrically anti-iced when the start lever is out of the cutoff position.
Icing of the Pt2 EPR probe is indicated by abnormal EPR indications.


Engine Anti-Ice - CF6 Engines:

The engine inlet cowl is anti-iced by pressure-regulated engine bleed air routed through the nacelle anti-ice valve to the inlet cowl area.  The anti-ice valve is electrically controlled from the overhead panel; and when activated maintains a constant limited pressure indicated by the VALVE OPEN light being illuminated.  If a valve malfunction allows higher than normal pressure air into a nacelle anti-ice system, the NAC TAI VALVE light illuminates.


Wing Anti-Ice:

The WAI system routes engine bleed air to the wing leading edge area.  To prevent possible damage to the leading edge flaps, anti-icing should be turned on prior to extending flaps.
When turning the system off, monitor the valve light until extinguished.  When the airplane is on the ground, the system is deactivated by the landing gear tilt switches.  A ground test switch position is provided to check valve operation.  During the ground test, the valve automatically closes when wing leading edge temperatures become excessive.


Window Heat:

The pilot's No. 1 windows are electrically heated using proportional heat controllers.  When turning on window heat, electric current is applied to the windows taking approximately six minutes to obtain full heating.  When an overheat condition existings, the controller cuts off power to the affected window. 
The pilot's No. 2 and No. 3 windows are electrically heated with a constant heating power.  A temperature controller thermostat in each window regulates power to the window.
The interior surfaces of the No. 1 windows are slow to heat.  Both the exterior and interior surfaces of the No. 2 and no. 3 windows are slow to heat.
Conditioned air may be used for internal surface defogging.  If operating at altitude after the loss of heat to a No. 1 window, anti-fog protection can be obtained by anticipating fogging during descent.  Thirty minutes priot to descent all pack valves should be operated in the full flow position and the recirculation fan for Zone 1 switched on to increase cockpit airflow.  For maximum defogging, cockpit conditioned air temperature should be increase to 17C (80F), affected windshield control opened and the respective foot-air control closed.

Note:  An anti-static coating is applied to the outer windshield layer.  With window heat voltage applied a shock hazard exists for personnel contacting the windshied from the outside.



Limitations

Min N1 RPM in Icing Conditions: 50% N1 at or above 10,000 feet; 45% N1 below 10,000 feet; 70% N1 with no Hi Stage bleed.

On the ground and for takeoff: Outside air temperature 50° F (10° C) or below, visible moisture in any form is present (clouds, fog with visibility of one mile or less, rain, snow, sleet, or ice crystals).

Ramp, Taxiway, and Runway conditions where surface snow, ice, standing water or slush may be ingested by the engine or freeze on engine, nacelle or engine sensor probes.           

In-flight: Total air temperature 10° C or below, visible moisture in any form is present (clouds, fog with visibility of one mile or less, rain, snow, sleet, or ice crystals

Comments