2.
  HMU-The hydromechanical unit has numerous functions, 3 main functions include: LDS (collective input), PAS (power control lever input), and the Torque Motor (ECU - engine governor) input.

   3.
  Starter-The pneumatic starter is powered by bleed air, typically from APU, it motors the Ng section via the AGB and PTO. It decouples (via internal clutch) from the AGB when the engine is running. Starter limitations exist because the bleed air powering it is hot (400oF) and can damage the starter if exposure time is excessive.

   4.
  IPS Blower-The Inlet Particle Separator (IPS) blower suctions dirty air from the collector scroll and blows it overboard, operates at high RPM's (30,000 rpm at 100% Ng) in a Foreign Object Damage (FOD) rich environment.

4. LEARNING STEP/ACTIVITY No. 4. Identify the operational characteristics of the engine start system.
a. Engine Start System-The UH-60 has an automatic start system that simplifies engine start by controlling various pneumatic and electrical systems during the engine start process.  The primary switches and controls associated with engine start include the PCL and the air source heat/start switch.  The PCL sets the fuel flow limits and houses the start override and abort switches.  The air source heat/start switch selects the air source to be used for the engine start.  Of the possible air sources available to start the engine, the APU is the most common.  Other available air sources used to start the engine include an external source, or the other engine.
(1)
Automatic Start System-The starter button on the PCL activates the automatic start system when the PCL is in the "OFF" position.  When the auto start is activated, a start relay controls and activates several functions.  They include:

.  
Main function: allows the engine start valve to open, illuminating the starter caution light. The engine start valve directs compressed air to the pneumatic starter and the starter motors the Ng section (AGB to the PTO) for engine start.  

.  
Additional functions: activation of the ignition and auto prime, deactivation of the cockpit heater and engine inlet anti-ice, closing the APU start/bypass valve (Turbomach APU only), and arms the override switch in the PCL.

b.
Engine Start Overview

(1)
While the Ng is being motored by the pneumatic starter, the PCL is advanced to "IDLE", which starts the fuel flow causing the engine to "light off" and accelerate up to idle speed (minimum 63% Ng).  During acceleration to idle, a speed sensor on the starter feeds the Ng speed information to the speed switch (auto start circuit).  The speed switch commands the starter valve to open until the Ng speed reaches a minimum of 52% Ng.  Between 52 - 65% Ng, the start valve will close extinguishing the starter caution light.
　
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