A. The Wing Thermal Anti-Icing (TAI) System is subject to ground and flight
operation. The system may be operated continuously on the ground or in-flight.
During ground operation, with the wing TAI system on, the wing leading edge is
protected from overheat by two 125°C thermal switches which automatically close
the wing TAI system shutoff valves if the air temperature is greater than 125°C.
The wing TAI shutoff valves are automatically closed when the left or right
throttle lever angles exceed approximately 32 degrees. The system will
automatically recycle the wing TAI system shutoff valves to the open position
when the left and right throttle lever angles are less than approximately 32
degrees and the air temperature is less than 125°C. For ground operation, the
precooler control valves controlled by external solenoid valves, will actuate
wide open. Should the wing TAI switch be left in the on position during taxi and
takeoff, the switch automatically returns to the OFF position at airplane
liftoff. In flight operation requires manually switching of the system.
B. The wing thermal anti-icing (TAI) system removes ice buildup on the wing
leading edge slats. The system receives regulated hot air from the pneumatic
manifold. The flow of air is controlled by a shutoff valve for each wing. Both
valves are operated by a single control switch on the pilot's overhead panel.
When the system is in operation, the valves direct air through a distribution
system to the wing leading edge slats. The system consists of supply and
distribution ducting, two control valves, electrical control components, thermal
switches and indicating components.
2. Wing Anti-Ice Ducting
A. The pneumatic air duct is connected to each of the wing leading edge supply
ducts through a control valve located in the wing leading edge just inboard of
the wing strut closure rib on each side of the airplane (Fig. 1). The wing
supply ducts are connected to each of the wing leading edge slats by telescoping
ducts. The telescoping ducts consists of two tubes, one of which slides within
the other as the slats are extended or retracted, and are sealed by an O-ring
between them. The inner telescoping duct is connected to the wing TAI supply
manifold ducts by a swivel T-connection to allow rotational movement of the
telescoping duct around the wing supply duct. The T-connection is sealed by an
O-ring between each end of the T and the supply duct. The outer telescoping duct
is connected to a slat anti-icing spray duct by a swivel T-connection to allow
rotational movement of the telescoping duct about the slat anti-icing spray
duct. A support bracket in the slat leading edge supports the ends of the slat
spray ducts and the telescoping duct and prevents the TAI air from flowing back
through the telescoping duct cut-out in the slat beam. The slat anti-icing spray
duct runs the full length of the slat and has perforations to direct the air
towards the slat leading edge. The air then flows between the slat upper skin
and the slat beam where the air is exhausted overboard through openings in the
slat lower skin.
B. To compensate for wing flexing, duct misalignment, and thermal expansion, the
ducts inboard of approximate slat station 175 are rigidly held and duct movement
is absorbed by the swivel joints at each telescoping duct connection and by
expansion bends in the duct routing.
Wing Thermal Anti-Icing System Equipment Location
3. Wing Anti-Ice Control Valves
A. The flow of air into the wing TAI system is controlled by a wing TAI shutoff
valve for each wing supply duct. The valves are located in the wing leading edge
just inboard of each engine strut outboard seal rib (Figure above) and are
2-1/2-inch diameter electric motor-driven butterfly valves which operate on
115-volt ac power. Access to the valve is through an access door in the lower
fixed leading edge. The valves are equipped with limit switches to prevent
overrunning of the motor and valve position indicator switches which are used in
the valve position indicator circuits. Each valve is equipped with an external
valve position indicator to verify valve position and have manual override.
4. Wing Anti-Ice Control Components
A. The operation of the wing anti-ice control valves are governed by the
following electrical control components; main and nose landing gear safety
relays, a WING ANTI-ICE control switch, valve control relays, two ground
overheat thermal switches, two transistorized circuit cards and two throttle
position switches.
B. The safety relays are energized by the main gear safety sensor and nose gear
safety sensor when the airplane is on the ground. The relays are used to provide
a ground for operation of the system on the ground.
C. The WING ANTI-ICE control switch is located on the P5 overhead panel. The
switch is a two position magnetic-trip switch. During ground operation of the
wing anti-ice system, the WING ANTI-ICE switch remains in ON position but will
automatically return to OFF position at airplane liftoff. In-flight operation
requires manual positioning of the switch for system operation.
D. The relay directs 115-volt ac power from the WING A/I circuit breakers to
close the wing anti-ice control valves when de-energized and to open the valves
when the relay is energized. The relay is controlled by transistorized circuitry
in conjunction with the safety relays, the control switch, two throttle position
switches and the ground overheat thermal switches.
E. The transistorized circuitry controls the indicating lights.
F. The ground overheat thermal switches are located at the root end of each wing
leading edge distribution manifold. The switch is a temperature sensitive
bimetallic-type switch with normally open contact points which close at
approximately 125°C. Actuation of either switch, while the airplane is on the
ground, will complete a circuit to close both wing anti-ice valves.
5.Wing Anti-Ice Indicating Components
A. The wing anti-ice system is provided with a blue light for each control valve
to indicate valve position. The lights are of the press-to-test type and are
located on the overhead panel adjacent to the WING ANTI-ICE system control
switch. The L VALVE OPEN and R VALVE OPEN indicating lights glow dimly whenever
the respective valve is in the open position, and brightly whenever the
respective valve position does not agree with the control switch position due to
a system malfunction or during valve transit. The light may be tested through
the use of the master light test switch. Refer to Chapter 33, Control Cabin
Lighting, for the master test switch.
B. Each valve indicating light is controlled by transistorized circuitry. The
system control switch must be in ON position. The transistorized control
switches are on printed circuit cards mounted behind the overhead panel. The
transistorized light control switches are supplied 28-volt dc power from the A/I
control circuit breaker.
6. Operation
A. The wing anti-icing system is controlled manually by the WING ANTI-ICE
control switch on the overhead panel. The wing anti-icing system may be operated
continuously on the ground or in-flight. Actuating the WING ANTI-ICE switch to
the ON position opens the wing TAI control valves and allows pneumatic air to
flow through the wing leading edge anti-ice ducts. During ground operation, when
the WING ANTI-ICE switch is on, a solenoid valve in each engine strut will open
and vent the precooler control valve sensor line to ambient and will allow the
precooler control valve to move to the full open position. The wing leading edge
is protected from overheat by two 125°C thermal switches which automatically
close the wing TAI system shutoff valves. In addition, the wing TAI shutoff
valves are automatically closed when the engine throttle lever angle is 32° or
greater. The system will recycle the wing TAI system shut-off valves to the open
position when the engine throttle lever angle is 32° or less and the air
temperature is less than 125°C. During taxi and takeoff, the WING ANTI-ICE
switch may be left in ON position but will automatically return to OFF position
at airplane liftoff. In-flight operation requires manual switching of the
system.
B. The L VALVE OPEN and R VALVE OPEN indicator lights provide an indication of
the respective valve position. The light will glow bright if the valve position
disagrees with the control switch position. The light will glow dim if the valve
is open and the control switch position is in ON position. The light will not
come on if the valve is closed and the control switch is in the OFF position.
