CAUTION: To avoid damage to the engine start switch actuators, do not move the ENG POWER CONT lever from IDLE to OFF while pressing the starter button.
(2)
The pilot may abort the auto start by pulling down on the PCL. This actuates the abort start switch and closes the starter air valve. In the event of an auto start malfunction, the pilot may complete a manual start by pressing, and holding the starter button during the start process, and releasing the button when the Ng speed reaches a minimum of 52% Ng.
c.
Pneumatic System
(1)
The pneumatic system is comprised of a series of tubing and valves that distribute compressed air to bleed air dependant systems. Compressed air originates from four sources: the APU, No. 1 engine, No. 2 engine, or external. The pneumatic system routes the compressed air from the source,
generally the APU, to start the engines, cabin heater, pressurize the Extended Range Fuel System (ERFS), or to export air to another helicopter for buddy start.
(2)
Engine Start Valves-The engine start valves are located inside the oil cooler compartment, inboard of each respective engine's firewall. The engine start valves are electrically controlled, and air actuated to allow bleed-air to flow through to the engine starter.
When the starter switch is pressed, the engine start valve is electrically opened by the solenoid valve. Opening the engine start valve allows compressed air from the air source to motor the air turbine starter of the engine being started. The air entering the engine start valve is filtered to remove impurities from the air as it passes through the engine start valve.
(3)
Crossbleed Valves-The crossbleed valves are electrically controlled and air actuated to allow bleed-air to flow through to pressurize the entire pneumatic manifold. The actuation of the crossbleed valves is accomplished through the air source heat/start switch and the automatic start system.
The crossbleed valve is electrically actuated and pneumatically opened. An electric solenoid allows the crossbleed valve to open when air is being forced out. The start relays prevent the crossbleed valve and engine start valve from being opened at the same time. There is no cockpit indication of valve position; a mechanical valve position index mark is located on the valve shaft.
(4)
APU Start Bypass Valve-The APU start bypass valve is located on the lower left hand side of the APU combustion chamber on the Turbomach APUs. They are not required on the Garret APUs due to a better fuel control. The APU start bypass valve is an electrically actuated valve that allows excess air to be dumped overboard until needed for engine start. The valve, "armed" when the air source heat/start switch is in the APU position, opens to unload the compressor during the start sequence, preventing compressor stalls.
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