SYSTEM DESCRIPTION (cont)
BLEED AIR INPUT
AND FRONT FRAME
TO SWIRL FRAME
AntiIce and Start Bleed Valve Operation
(4) Engine Start Subsystem.
The starting system (fig. 417) uses air from the PAS and provides means
for starting each engine. When the pilot power quadrant MASTER IGN switch is set to ON, 28 VDC is supplied to
the ENG START switch. Setting the ENG START switch momentarily to START initiates an automatic start
sequence which sends a 28 VDC signal to the start relay in the engine start mode relay panel. The start relay
sends the following signals:
Regulator energize to the engine. The engine air pressure regulator opens, supplying PAS air to
the air turbine starter. The ECU/DECU sends a signal to the pilot power quadrant which lights the
ENG 1 or ENG 2 START indicators.
Interlock valve to the ENCU shutoff valve. The valve closes to ensure all PAS air is available to
drive the air turbine starter.
Ignition enable to the engine ignition system. The ignition system supplies electrical ignition to the
Speed control switch to the engine speed cutout switch in the electrical power distribution box.
This maintains the start sequence after the ENG START switch is released.
When the engine starts it sends speed sensor to the engine speed cutout switch. The switch
opens, ending the start sequence.