Anti-Ice
Thermal anti-ice uses bleed air from the pneumatic system to heat:
- Engine cowl lip
- 3 inboard leading edge slats
Electrical power is used to heat:
- Pitot probes
- Auxiliary pitot probe
- Alpha vanes
- Temp probe
- Elevator pitot probe
- Flight deck windows
Note that the static ports are not heated.
Additionally, the forward flight deck windows are equipped with windshield wipers. Conditioned air can also be used to defog the windshield.
Most controls are on the overhead panel, including:
- Window heat panel
- Windshield wiper select panel
- Probe heat panel
- Wing and engine anti-ice panels
- FOOT AIR and WINDOW AIR panels
Anti-ice bleed air
Engine cowl anti-ice
Engine cowl anti-ice valves control the flow of hot bleed air to the engine inlet cowl. They are located upstream from the engine bleed air valves. This location allows the operation of engine anti-ice regardless of bleed air valve position.
The inlet cowl valves are electrically controlled and pneumatically operated, and spring loaded into the closed position. The engine anti-ice system controls the respective anti-ice valve either open or closed - with the requirement that pneumatic pressure is available to open the valve. With the anti-ice switches set to ON opens the valves and allows the engine inlet cowl to be heated.
This also reconfigures other other systems for possible aircraft icing:
- the EECs reset to Approach Idle,
- the stall warning logic adjusts stick shaker,
- and minimum speed bars on airspeed indicator
These system return to normal when the ENG ANTI-ICE switches are selected OFF if wing anti-ice has not been used in flight.
ENG ANTI-ICE must be ON for all flight operations when icing conditions exist or are anticipated, except climb and cruise where the temperature is >-40 C SAT.
The blue COWL VALVE OPEN status lights indicate that the cowl anti-ice valve position disagrees with the related switch position, or that the valves are in transit. Thus when selecting engine anti-ice on, the lights will illuminate bright momentarily. Once the transit period is over, the lights illuminate dim.
Simultaneously, green TAI indications appear on the N1 display.
An amber COWL ANTI-ICE light may illuminate. This indicates an over pressure condition in the duct downstream of the engine cowl anti-ice valve. Note: this is NOT temperature related.
Wing Anti-Ice
On the ground, this system can be used as deice or anti-ice.
It uses hot air from the pneumatic system to heat the three inboard leading edge slats of each wing. It does not include the leading edge flaps or outboard leading edge slats.
Selecting the system on opens the wing anti-ice valves and allows bleed air into ducts connected to the leading edge. The air then exhausts through holes in the bottom on the slats. The system allows hot bleed air to enter the wing’s pneumatic ducts through two AC motor-operated valves.
Note that the valves are electrically controlled.
While on the ground, if either distribution duct thermal switch is activated the control valves close to protect the slats from overheating. This is only available on the ground.
Blue L & R VALVE OPEN status lights on the WING ANTI-ICE panel function is much the same way as the COWL VALVE OPEN anti-ice lights.
Wing anti-ice will be automatically shutoff during take-off to preserve thrust on both engines. This will occur as the thrust levers are advanced beyond the thrust warning setting. Note, however, that if thrust on both engines is below takeoff warning setting and temperature inside both distribution ducts is below thermal activation temperature, the wing anti-ice valves will open.
Once the PSEU transitions into air mode, the WING ANTI-ICE switch will trip to off.
Like the ENG ANTI-ICE switch, the WING ANTI-ICE switch will reconfigure some systems:
- Stick shaker logic set for icing conditions
- Minimum maneuver speed bars on airspeed indicator adjust
Additionally, the stall warning logic will remain set for icing for remainder of flight, regardless of subsequent ANTI-ICE switch position. This is because the entire wing was not heated.
Window heat
Flight deck window heat prevents ice formation, fogging, and improves window impact strength.
When electrical power is applied to the selected windows, green ON status lights illuminate on the overhead panel. If a window temperature exceeds target temperature, the ON light will extinguish.
The OVHT PWR TEST can be used as a confidence test of a window when a window heat switch is ON and the corresponding green ON light is not illuminated.
Should window temperatures exceed a predetermined limit, an overheat is detected and the amber OVERHEAT light will illuminate and power will be removed from the respective window (green ON light should extinguish). Note that the light will also illuminate if electrical power to the window is interrupted.
Probe heats
During standby power, the auxiliary pitot probe (used for the standby airspeed indicator) is not heated.
The controls have two modes: AUTO and ON. In AUTO mode no electrical power is supplied to the probes until the first engine is started. In the ON position electrical power is supplied to all probes.
PROBE A switch controls:
- CA Pitot Probe
- Left Elevator Pitot Probe
- Left Alpha Vane
- TAT probe
PROBE B switch controls:
- FO Pitot Probe
- Right elevator Pitot Probe
- Right Alpha Vane
- Auxiliary Pitot Probe
Amber lights on the Probe Heat Panel indicate that the respective probe is not heated.
Which anti-ice systems use bleed air?::Engine cowl lip and inboard leading edge slats
Which anti-ice systems use electrical power?::Pitot probes, elevator pitot probes, alpha vanes, temperature probe, flight deck windows.
What systems are reconfigured with ENG ANTI-ICE on?::EECs reset to Approach Idle, stick shaker logic is adjusted, and minimum speed bars on airspeed indicators increase. When must ENG ANTI-ICE be on?::All operations where icing exists or is anticipated, except climb and cruise with temperatures >-40 C SAT.
What does an amber COWL ANTI-ICE light indicate?::An over pressure condition downstream of the engine cowl anti-ice valve (this is NOT temperature related). Are all anti-ice system valves pneumatically operated?::No, wing anti-ice valves are electrically controlled and operated.
Is there slat overheat protection for the wing anti-ice system?::Yes, but only on the ground.
After switching WING ANTI-ICE off, will stall warning logic return to normal?::No, once WING ANTI-ICE is activated the stall warning logic remains set for icing conditions regardless of any subsequent anti-ice switch position for remainder of flight. What causes window OVERHEAT lights to illuminate?::Exceeding predetermined temperature or interruption of electrical power. What is controlled by the PROBE A and PROBE B switches?::Probe A is left side pitot probe, elevator pitot, and alpha vane. Probe B is same for right side. Left side includes TAT probe while right side includes Auxiliary Pitot Probe.
How are the Engine Anti-Ice valves controlled?::Electrically controlled, pneumatically operated.
While in flight the wing anti-ice valves automatically close during an overheat.::False, auto-shutoff is only available on the ground.
What is the position of the Wing Anti-Ice valves after takeoff thrust has been set with the switch on?::The wing anti-ice valves automatically close. The static ports are heated when the PROBE HEAT switches are selected on.::False, the static ports are not heated.
What does an amber light indicate on the Probe Heat Panel?::That the respective probe is not heated.