TM 1-1520-238-T-4
4–23
4–7
SYSTEM DESCRIPTION (cont)
4–7
(3) Engine Anti–Ice.
The engine anti ice system prevents icing of the engine air inlets and the NGB.
(a) Heater blankets in each NGB fairing (fig. 4–15) prevent ice from forming on the gearbox coupling fan
and air duct to the main transmission deck. The heater blankets operate as follows (fig. 4–15): ECS ENG
ANTI–ICE circuit breaker (CB67) supplies 28 VDC through the electrical power distribution box to the pilot ANTI
ICE panel. Setting the anti ice ON/OFF switch to ON sends a signal through the electrical power distribution box
to a heater controller in each engine NGB fairing. ECS R NOSE GRBX HTR circuit breaker (CB211) and ECS L
NOSE GRBX HTR circuit breaker (CB212) supply 115 VAC power to the heater controllers. When the heater
controllers receive the signal from the pilot ANTI ICE panel, they send 115 VAC to the engine NGB fairing heater
blankets. The heater blankets provide heat to warm the NGBs to approximately 225 to 235 F (107 to 112 C).
The heater blankets return sensor signals to the heater controllers. If a heater overheats or fails, the controller
sends an NGB HEATER FAIL signal to the caution/warning panels in both crew stations which lights the pilot
ENG 1 ANTI ICE or ENG 2 ANTI ICE indicators, and the CPG ENG ANTI ICE indicator.
(b) Each engine has an anti–ice and start bleed valve which is spring–loaded open. It can be closed
either mechanically by the HMU or electrically by the pilot ANTI ICE control panel controlled solenoid. The start
bleed valve controls anti–icing airflow to the engine and bleeds air from the compressor during engine starting and
low engine speeds. During starting and at low engine rpm, the HMU actuator positions the cam plate to open the
valve. The valve closes at 91% NG rpm or 60% torque, whichever occurs first (fig. 4–16). When energized, the
solenoid opens to allow fifth stage air to enter the servo and close the metering valve against spring pressure in
the servo. De–energizing the solenoid closes off the fifth stage air and vents the servo, allowing the servo spring
to open the metering valve. If power to the solenoid is lost, the valve opens. If the metering valve fails to open
when the solenoid is de–energized, the metering valve shaft closes a sensing switch. This lights the ENG 1 ANTI
ICE or ENG 2 ANTI ICE indicator on the pilot caution/warning panel and the ENG ANTI ICE indicator on the CPG
caution/warning panel.
PILOT ANTI ICE PANEL
PILOT AFT
CIRCUIT BREAKER PANEL
ECS ENG ANTI - ICE
CB67
28 VDC
ECS R NOSE
GRBX HTR
CB211
115 VAC
3Ø
28 VDC
ON
ELECTRICAL POWER
DISTRIBUTION BOX
ON
115 VAC
CONTROLLER
HEATER
BLANKET
115 VAC
SENSOR
ENGINE NGB FAIRING
(TYPICAL)
NGB
HEATER FAIL
PILOT
CAUTION /
WARNING
PANEL
CPG
CAUTION /
WARNING
PANEL
M58-211
ECS L NOSE
GRBX HTR
CB212
115 VAC
3Ø
Figure 4–15.
NGB Fairing Heater Block Diagram
