b. Engine Modules-The four modules of the engine can be associated with two sections, Ng and Np. The Ng section (Gas Generator) is the part of the engine that makes the power:  the cold, hot, and accessory modules make up the gas generator. The Np section (Power Turbine) converts the Ng's gas pressure into rotational shaft energy that is transferred to the helicopter drive train. The power turbine is represented by it's own module. Keep in mind that operational knowledge of the engine and its instruments revolves around the understanding of the two main operational sections of Ng and Np, which operate within the four modules.
(1)
Cold Section Module-The cold section module includes the inlet particle separator, compressor, diffuser and midframe case (surrounds the combustion chamber), the output shaft assembly, and various Line Replacement Units (LRU). The cold section has mounting points: a forward support tube secures the engine in its fore-aft axis to an elastomeric gimble on the input module. Aft mounts secure the engine in its radial axis to the deck through spherical bearings that allow the engine to move fore and aft as the forward mount flexes. This mounting arrangement makes the engine to the airframe connection flexible, which dampens vibrations and compensates for the flex of the airframe.

(a)
Output Shaft Assembly-The output shaft assembly (highspeed shaft) is splined into the engine and bolted to the input flange of the input module. A flexible coupling and balance studs are attached to the highspeed shaft and input flange to minimize vibrations and provide centering of the shaft. The highspeed shaft delivers engine power (from the power turbine) to the helicopter. The highspeed shaft rotates at 20,900 rpm when Np is 100%, and there is no gear reduction in the engine.

(b)
Swirl Frame-The inlet section includes the components forward of the compressor. The components are the swirl frame, mainframe, output shaft, front frame, and scroll case. These, together with the inlet duct and blower, make up the engine inlet particle separator. Air enters the separator through the swirl frame. Swirl vanes direct the air into a rotating or swirling pattern to separate sand, dust and other foreign objects by centrifugal action. These particles are carried to the outer section of the main frame, through a series of scroll vanes and into the scroll case. The particles are sucked from the scroll case by the blower and are blown out through an airframe supplied overboard duct. Air that remains after particle separation is carried to the front frame deswirl vanes, straightened and directed to the compressor inlet. Relatively clean air (approximately 85% of total) from the center of the rotating air mass is directed into the axial compressor. The inlet particle separator blower (IPS) evacuates the remaining dirty air (15% of total) from the collector scroll and discharges (blows) it overboard.

(c)
Inlet Particle Separator Blower-The particle separator blower removes sand, dust, and other foreign material from the engine inlet air. Engine inlet air passes through the swirl vanes, spinning the air and throwing dirt out by inertial action into the collector scroll. The foreign material is drawn into the blower and discharged overboard around the engine exhaust duct. Pilot considerations about the IPS blower are: during start-up and shut-down, when the Ng speed is low, the IPS blower is not effective. Also, it is not effective against sheet ice shed from the windshield, which is due to the shape of the ice.
　
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