(3)
If the position of a wing's TAI valve disagrees with its commanded position, that wing's VALVE light illuminates.
(4)
EICAS computers monitor valve/switch disagreement. If valve position disagrees with commanded position for more than 2.5 seconds, a wing anti-ice message is shown on EICAS display P2 (AMM 31-41-00).
(5)
Engine bleed control cards (EBCCs) monitor TAI valve position. The EBCCs have outputs to the electronic engine control unit (EEC). The EEC readjusts engine trim to meet changing bleed air requirements (AMM 73-21-00).
(6)
A capped test port downstream of the TAI valve allows on-the-ground checking of duct pressure.
B. Ground Test
(1)
An air/ground relay prevents system operation on the ground. A ground test can be performed with the WING ANTI-ICE WINDOW/PROBE HEAT switch on the M10398 test panel. The switch is a three position, spring loaded, center off switch. Test indications depend on the position of the WING ANTI-ICE switch (on P5).
(2)
With the WING ANTI-ICE switch off, holding the test switch in the WING ANTI-ICE position will open the TAI valves. The VALVE lights will be illuminated as long as test switch is held up to a maximum of 12 seconds. A ground safety time delay relay automatically closes the valve after 12 seconds to prevent duct overheating. Retesting can only be performed by releasing and then holding the test switch.
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A
757
MAINTENANCE MANUAL
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28V DC WING
WING ANTI-ICE
ANTI-ICEWIND/
P11 PROBEHEAT WING ANTI-ICEAND WINDOW/PROBEHEAT SWITCH
WING ANTI-ICE
MASTER
DIM &
AA TEST PANEL
L/R EICAS COMPUTERTEST L/R VALVE LT
ENGINEBLEED AIR
NOT DISAGREE RELAYL/R WING
OFF CLOSED
CLOSED
CARD
