The pneumatic system of the UH-60 operates from bleed air furnished by the main engines, APU, or an external air source. The pneumatic system consists of the engine start system, the anti-ice system, the heating system, and the extended range fuel system.

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Bleed air supplied by a main engine, the APU, or an external air source can be used for starting purposes. The normal means of starting is through use of the APU as an air source. The APU can provide sufficient air pressure and volume to accomplish single engine starts throughout a wide range of ambient conditions and to accomplish a dual engine start when conditions permit. Chapter 5 of the operator’s manual lists engine start envelopes for given ambient conditions.

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Engine starts may also be accomplished by using an operating engine as an air source, and are known as cross bleed starts. Cross bleed starts can be accomplished providing the Anti-ice light on the source engine is off, NG for the source engine is above 90%, and NR is 100%. If an engine is to be used as an air source, the Air Source Heat Start switch must be placed in the engine position.

The heater system is pressurized by bleed air from any of the sources listed above. The heater system mixes ambient air with heated bleed air to provide warm air to the crew stations and to help prevent the overhead windows, and gunner’s windows from fogging. The heater will automatically disengage when the starter is engaged. Heater use will reduce max torque available by 5%.

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The engine anti-ice systems consist of the engine anti-ice and engine inlet anti-ice systems. Both anti-ice systems utilize bleed air from their respective engine only. The APU and external sources are not used for the engine anti-ice systems. The engine anti-ice system utilizes bleed air extracted from the compressor of the engine. This bleed air prevents ice formation on the vanes in the inlet. Anti-ice functions are controlled by the pilot through a switch labeled #1 Eng Anti-ice or #2 Eng Anti-ice. Placing the Eng Anti-ice switch to on, results in the anti-ice start bleed valve remaining open. This action directs heated air to inlet vanes. An advisory light labeled #1 Eng Anti-ice On or #2 Eng Anti-ice On will illuminate when the anti-ice start bleed valve opens.

These lights will also illuminate during low power conditions (88-92% NG), because the anti-ice start bleed valves open to dump excess compressor discharge pressure preventing the possibility of an engine flameout. Engine anti-ice use will reduce max torque available per engine by 20%.

The engine inlet anti-ice is controlled by the same switch listed above, but utilizes air from a separate bleed air tap. Bleed air is routed directly to the engine inlet anti-ice modulating valve. When the engine anti-ice switch is placed on, the anti-ice modulating valve samples ambient temperature through the insulated ambient sense port. If the ambient temperature is above 13ºC the modulating valves may not open. If the ambient temperature is between 4ºC and 13ºC, the modulating valves may open. If the ambient temperature is below 4ºC, the modulating valves must open. When the modulating valve opens, heated bleed air is forced through the airframe engine inlet and out the slits on the inlet. When the inlet temperature reaches 93ºC, an advisory light labeled #1 Eng Inlet Anti-ice On or #2 Eng Inlet Anti-ice On will illuminate. The illumination of the #1 and #2 Eng Inlet Anti-ice On light indicates proper system operation.