TM 1-1520-238-10 2-61 AIR DATA DC circuit breaker to the left wing pitot heater. Both circuit breakers are on the pilot overhead circuit breaker panel. The AIR DATA DC circuit breaker also pro- vides 28 vdc to the ADS control relay. When energized, this relay sends 115 vac from the No. 1 essential ac bus through the AIR DATA AC circuit breaker to the air data sensor for anti-icing. In addition, the CPG AUX panel ADSS switch, when set to on, energizes the ADS control relay to provide the air data sensor with 115 vac from the No. 3 essential ac bus through the AIR DATA AC circuit breaker. 2.43.3 PNVS and TADS Anti-Ice/De-Ice. Three posi- tion TADS/PNVS toggle switches on the pilot ANTI-ICE panel and the CPG AUX/ANTI-ICE panel control the op- eration of the TADS/PNVS window heaters. These switches receive 28 vdc from the No. 1 essential dc bus through the CANOPY ANTI-ICE CONTR circuit breaker. Window heating is automatically controlled by a thermal control sensor in the respective heater power return cir- cuits. a. In Flight TADS/PNVS Anti-Ice/De-Ice. With the helicopter in flight and the pilot or CPG TADS/PNVS switch set to ON, the squat switch relay closes to provide 28 vdc from the pilot or CPG TADS/PNVS switch to the MRTU. This causes the MRTU to send a signal to ener- gize anti-ice relays in the TADS power supply and PNVS electronic unit. The TADS and PNVS anti-ice relays then provide the TADS and PNVS window heaters with 115 vac from the No. 1 essential ac bus through the TADS AC on the CPG circuit breaker panel and the PNVS AC circuit breakers on the pilot overhead circuit breaker panel. b. On Ground TADS/PNVS Anti-Ice/De-Ice. When the helicopter is on the ground, the squat switch opens re- moving power from the TADS/PNVS switches and the TADS and PNVS window heaters. When either TADS/ PNVS switch is set to GND, a signal is sent to the MRTU which energizes the TADS/PNVS anti-ice relays. These relays then provide the TADS and PNVS window heaters with 115 vac from the No. 1 essential ac bus through the TADS AC and PNVS AC circuit breakers. 2.43.4 Engine Inlet and Nose Gearbox Anti-Ice. En- gine bleed air is used to heat the engine air inlet, and heat- er blankets are used to anti-ice the nose gearbox. Engine anti-ice protection is controlled by a ENG INLET ON/OFF toggle switch on the pilot ANTI-ICE panel. In the ON posi- tion, ENG 1 and ENG 2 advisory lights located above the switch will illuminate when the system is functioning prop- erly. The engine anti-ice valves and engine gearbox heat- er blanket controller receive 28 vdc from the No. 1 essen- tial dc bus through the ENG ANTI-ICE circuit breaker on the pilot overhead circuit breaker panel. The ENG INLET switch in the OFF position energizes both engine anti-ice valves to the closed position. In the ON position, the ENG INLET switch deenergizes the anti-ice valves thus allow- ing them to open and furnish hot air to the engine inlet for anti-icing. It also energizes the engine gearbox heater blanket controller. The energized controller allows 115 vac to be supplied from the No. 1 essential ac bus through the NOSE GRBX HTR circuit breaker on the pilot overhead circuit breaker panel for the nose gearbox heater blan- kets. 2.43.5 Rotor Blade De-Icing System. The rotor blade de-ice three-position ON, OFF, and TEST toggle switch, located on the pilot ANTI-ICE panel receives 28 vdc from the No. 3 essential dc bus through the BLADE DE-ICE CONTR circuit breaker on the pilot overhead circuit break- er panel. In the ON position, the switch will provide 28 vdc power to the main rotor and-tail rotor de-icing controller and turn on the controller. When the controller is turned on, it collects data from the signal processor unit, ice de- tector/rate sensor, and the outside air temperature sensor. If icing conditions are present, the controller will energize the blade de-ice control relay. The energized blade de-ice control relay provides a ground to the blade de-ice contac- tor control relay that receives 28 vdc from the No. 3 es- sential dc bus through the BLADE DE-ICE circuit breaker. With the blade de-ice contactor energized, 115 vac, 3 phase power is furnished from Gen 2 through the blade de-ice contactor to the de-ice controller. (Gen 1 will only furnish power when an overload is sensed on Gen 2, and the contactor is caused to trip). The de-ice controller recti- fies the 115 vac to 268 vdc ( 134 vdc) for the rotor blade heaters. The main rotor blades receive 134 vdc through slip rings at the main rotor distributor. The main rotor dis- tributor provides a sequential delivery to the blade heater elements. In the TEST position, the rotor blade de-ice switch provides that the controller will complete one full cycle of the blade anti-ice circuits. The tail rotor blades re- ceive 134 vdc from the de-icing controller through tail rotor slip rings. Power to the tail rotor blade elements and main rotor blade elements is controlled by the de-icing controller which times the amount of current allowed to the blades for heating. The de-icing controller will detect faults within the system. When a fault occurs, the controller shuts off power to the blades and illuminates the BLADE ANTI ICE FAIL segment on the pilot caution/warning pan- el.