OPERATING MANUAL
2A-73-00 PRODUCTION AIRCRAFT SYSTEMS
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HP Fuel Cock Positions
Figure 2
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-73-00
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2A-73-00 PRODUCTION AIRCRAFT SYSTEMS
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Engine Fuel System
Controls and Indications
Figure 3
OPERATING MANUAL
2A-73-00
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ENGINE IGNITION
2A-74-10: Engine Ignition System
1. General:
A. Description:
The ignition system, together with the cranking system, starts the engine
on the ground and independently in flight (to re-start the engine).
The function of the ignition system is to supply ignition to the fuel and air
mixture in the discharge of a series of sparks across the electrodes of the
igniter plugs (the igniters are in combustion liners No. 4 and No. 8 in each
engine). Combustion then passes between each liner through
interconnectors to complete the combustion cycle. The aircraft electrical
system supplies 28V DC to the high-energy ignition units, control is by the
start master switch and the individual start selector switches.
B. Operation:
During the start sequence (MASTER START and ENG START switchlights
to the ON position), the engine’s start relay energizes to supply 28V DC
power from the Essential DC bus to energize the respective ignition relay.
The ignition relay then closes to supply 28V DC bus to the ignition unit(s).
NOTE:
On aircraft SN 1000 thru 1143 with ASC 151 and 1144
thru subsequent, only one ignition unit and igniter plug
operate during ground starting, for example:
• Left Engine — No. 1 Ignition Unit
• Right Engine — No. 2 Ignition Unit
• With the ignition unit(s) energized, a green IGN
annunciation appears next to the engine’s HP RPM
display.
As engine RPM reaches approximately 38 to 45%, the starter’s centrifugal
cutout switch opens to de-energize the start and ignition relays. The
ignition unit(s) de-energize and the IGN annunciation clears.
Lifting the switch guard and pressing an AIR START IGN switchlight
supplies 28V DC directly from the DC bus to the corresponding ignition
units. With an AIR START IGN switchlight in on, the switchlight’s blue ON
caption illuminates and the green IGN annunciation appears next to the
engine’s HP RPM display on EICAS. When the ignition units are receiving
power through the AIR START IGN switchlight they operate continuously.
C. Subsystems, Units and Components:
(See Figure 2.)
The Engine Ignition system is composed of the following units and
components:
• Ignition Relay
• High Energy Transistorized Ignition Units (2 Per Engine)
• High Tension Leads (2 Per Engine)
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• Igniter Plugs (2 Per Engine)
2. Description of Subsystems, Units and Components:
A. Ignition Relay:
During ground starting, the ignition relay is energized when the starter relay
and pneumatic starter are energized. When energized, the relay provides
power from the Essential DC bus through the #1 IGN and #2 IGN circuit
breakers to the high energy ignition units. Each ignition unit is provided with
DC power from a separate circuit breaker.
B. High Energy Transistorized Ignition Units:
The ignition units change a low voltage DC electrical supply into a High
Energy (HE.) output. They can be energized independently of the engine
starting system if a re-start in flight is required. The components of the unit
are housed in a light alloy case. This case also carries a Light Duty (LD)
receptacle to connect it to the aircraft electrical supply and a HE receptacle
to connect it to the igniters.
C. High Tension Leads:
A high tension lead connects the ignition unit output to its igniter plug.
D. High Energy Igniter Plugs:
The engine has two HE igniter plugs, installed in the diffuser case at
numbers 4 and 8 combustion liner positions. The HE ignition unit supplies
power to the terminal connector of the plug. This electrical energy causes a
high intensity spark across the electrodes of each plug and supplies
ignition to the fuel and air mixture in the combustion chamber.
3. Controls and Indications:
(See Figure 1.)
NOTE:
A description of the Engine Instruments and Crew
Alerting System (EICAS) can be found in Section 5 of
Honeywell’s SPZ-8000 (or SPZ-8400) Digital
Automatic Flight Control System Pilot’s Manual for the
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