05/13/16
Overview
The engine nacelle anti-icing system does not let ice collect on the air intake. The anti-icing system uses direct, not pre-cooled, engine bleed air from the bleed air system. The temperature changes with the aircraft speed, the altitude, and the ambient temperature and is usually between LP 170 °F to 530 °F (77 °C - 277 °C), HP 271 °F to 764 °F (133 °C - 407 °C). Each anti-icing system takes the airflow from its related bleed air system.
The anti-icing system uses bleed air supplied by the high pressure (HP) compressor to make the front of the inlet cowl hot. Two ducts supply the air from the 5th stage of the HP compressor to the front flange of the low pressure (LP) compressor case. A cowl anti-icing valve which is installed between the ducts controls the supply of hot air. The duct system connects with the supply duct where the LP compressor case interfaces with the inlet cowl rear bulkhead. The supply duct is installed between the front and rear bulkheads in the bottom of the inlet cowl. It connects with a piccolo tube installed in the front part of the inlet cowl.
The airflow supplied to the wing anti-icing systems is adjusted by the anti-icing modulating-and-shutoff valves. These valves are controlled by the Bleed Management Controller (BMC) to keep the wing temperature at 239 °F (115 °C) to not let the ice collect on the wing slats and leading edge. The BMC receives data from temperature sensors installed on the inner side of the wing leading edge.
The flow control is duplicated by the monitoring channel of the BMC, which operates through the second probe found in the body of the anti-icing temperature sensor. One BMC channel does the control function. The other channel monitors, but also controls if the first channel is defective.
10/04/19
Cowl Anti-Ice Panel
The ANTI-ICE control panel is the lower part of the bleed air control panel. It has four three-position rotary switches, where two are L COWL and R COWL. The positions for each rotary switch are OFF, AUTO and ON.
Located on bleed air/air conditioning/anti-ice panel are two (left and right) cowl anti-ice switches. These rotary selectors (OFF-AUTO-ON) provide independent control of the left and right cowl anti-ice system. These positions perform the following functions:
Anti-Ice Panel
|
OFF |
The cowl anti-ice valve is forced closed by energizing the solenoid of the valve and having 5th-stage air available. |
|---|---|
|
AUTO |
The cowl anti-ice valve is automatically enabled when either ice detectors detect icing conditions. By removing power to the solenoid, the valve is spring-loaded to open. |
|
ON |
The cowl anti-ice valve is enabled to operate continuously providing sufficient bleed pressure is available from the engine. Also provides a discrete to the enhanced vision system (EVS) heater controller to activate the infrared window and fairing heaters. |
Bleed Air Synoptic
The cowl anti-ice synoptic page is combined with the bleed air and wing anti-ice synoptic. The cowl anti-ice synoptic displays:
Synoptic Displays
| Item | Green | Amber | White | Magenta | Cyan |
|---|---|---|---|---|---|
|
Cowl anti-ice valve outlines |
- - - |
Valve failed closed or open |
Normal |
Invalid data |
- - - |
Nose Cowl Ducting
Ducts supply the air from the 5th-stage of the compressor to the front flange of the compressor case. The duct system connects with the supply duct where the LP compressor case interfaces with the inlet cowl rear bulkhead. The supply duct is installed between the front and rear bulkheads in the bottom of the inlet cowl. It connects with a piccolo tube installed in the front part of the inlet cowl.
The hot air flows through holes in the piccolo duct directly on the inner surface of the inlet cowl. Used air is released through the outlet duct.
The engine mounted duct incorporates a venturi to limit total flow should any part of the engine mounted duct rupture. The venturi will also control total flow if any of the intake cowl components rupture with the control valve open.
The supply duct has a pressure transducer to sense system pressure.
05/13/16
Cowl Anti-Ice Valve
The cowl anti-ice (CAI) valve controls the flow of hot engine bleed air to the inlet cowl ducting. It is mounted on the lower right hand side of the engine adjacent to the starter motor. The valve can be accessed via a hinged access panel in the lower cowl door.
The cowl anti-ice valve is a spring-loaded-open, pneumatically-operated, electrically-controlled, pressure-regulating and shutoff valve. When the butterfly valve is open, compressor stage 5 air flows to the intake cowl spray ring.
The valve has a regulator housing and a short section of duct. The regulator housing has a bleed pressure-regulator valve. The valve, which is activated through a solenoid, controls the movement of the pneumatic actuator through a pressure reducer. The pneumatic actuator has a piston and a cylinder assembly which keep the pressure in the actuator upper chamber at a constant level. The pneumatic actuator also keeps the butterfly plate closed to stop the airflow when it is more than the permitted limit.
The duct section has a flange at each end for connection to the anti-icing air ducts. The butterfly plate which controls the airflow is installed in the duct.
Caution:
When aircraft electrical power is applied, and cowl anti-ice is selected OFF, the valve solenoid will be energized and get hot.
Note:
It may be necessary to isolate the electrical power to the valve during maintenance to prevent the valve from getting hot.This can be done by selecting the cowl anti-ice selector ON or by locking the appropriate circuit breaker through the EMS CDU.
The valve will open under spring force when the duct is unpressurized. When the solenoid is energized and there is sufficient duct pressure the valve will close. Upstream air pressure to operate the valve is tapped off from the 8th-stage bleed port.
To open the valve the solenoid is de-energized and a vent on the valve opens. As the upper chamber pressure is released through the vent it becomes less than the pressure in the middle chamber. The piston in the middle chamber pressure then moves to open the butterfly plate. If the system pressure changes, the regulator valve senses it and the plate is automatically adjusted. This changes the pressure in the upper chamber and changes the position of the butterfly plate to keep the anti-icing airflow to the air intake in limit. The valve will pressure regulate to 25 + 3 psi. The valve incorporates a microswitch. Closed position information is provided to the DAU and BMC. The valve can be manually locked open to allow aircraft dispatch with an inoperative valve.
Cowl Anti-Ice Pressure Transducer
The cowl anti-ice pressure transducer is installed on the inlet cowl rear bulkhead. It measures,through a pneumatic sense line, the air pressure downstream of the cowl anti-ice valve and supplies the information to the bleed management controller to produce the flow tube indications and system status on the bleed/anti-ice synoptic page.
System Operation
The cowl anti-ice system is controlled from the L-R cowl switches on the anti-ice panel in the flight deck.
In the OFF position the CAI valve solenoid is continuously energized forcing the valve closed (provided aircraft electrical power is on and bleed air available), thus ensuring no cowl anti-ice is available.
In the AUTO position the CAI valve will open when ice is detected by either ice detector. Relays K1 and K2 (located behind the control panel) receive power from the SPDA and are energized when the ice detector detects ice. The energized relay removes 28 VDC to the cowl anti-ice valve and enables the CAIV to operate.
Once “ICE” signal 2 is canceled from the ice detector, relays K1 and K2 are de-energized. This reapplies 28 VDC to close the cowl anti-ice valves.In the ON position the solenoid is de-energized and the valve will open. Either of the cowl anti-ice switches in the ON position also provides a discrete to the enhanced vision system (EVS) heater controller to activate the infrared window and fairing heaters.
The CAI valve full closed position switch indicates valve position to the BMC. This information is supplied to provide the valve position and status on the bleed/anti-ice synoptic page.
System Monitoring
The cowl anti-ice system is monitored by the bleed management controllers. EICAS messages and CAIMS reports are generated by the BMC.
Power On Built-In-Test
The cowl anti-ice system is not tested during PBIT.
Continuous Built-In Test
The following cowl anti-ice components are monitored during CBIT by the BMC onside.
During continuous built in test (CBIT) the following components are tested:
- Cowl Anti-Ice Valve (pressure regulating CAIP >40 / < 10 psig, failed closed)
- CAI Pressure Transducer (out of range, internal BMC CHA/B comparison)
If a failure is detected a CAIMS report is generated and, in certain failure cases, a CAS message is also generated
Bleed Air Synoptic
The cowl anti-ice synoptic page is combined with the bleed air and wing anti-ice synoptic.
Bleed/Anti-Ice Synoptic Page Symbols
The following represents the EICAS symbols and logic for the bleed/anti-ice synoptic page. The symbols are shown in serviceable and failure conditions.
