ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
ATA 74
IGNITION
For Training Purpose Only. 74-00-00 1| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
CONTENTS
DESCRIPTION ................................................................................................................................................................................................................................................... 3
COMPONENTS ................................................................................................................................................................................................................................................. 5
OPERATION...................................................................................................................................................................................................................................................... 7
Autoignition ................................................................................................................................................................................................................................................... 13
For Training Purpose Only. 74-00-00 2| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
DESCRIPTION
Each engine has an independent ignition system that consists of:
• Ignition unit
• Igniter plus and leads
• ENG IGNITION switch (Figure 74-1)
• IGN ON annunciator
For Training Purpose Only. 74-00-00 3| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
For Training Purpose Only. 74-00-00 4| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
COMPONENTS
The 731 engine has a high-energy ignition system consisting of a dual-circuit ignition unit (Figure 74-1) at the 1 o'clock position on the compressor
case. Power from the PE2 bus is supplied to the unit during engine starting. Ignition automatically occurs when the starting system is operating and the
associated HP lever is moved up to the ON position. Ignition may be selected for continuous operation by two ENG IGNITION 1 and 2 ON-OFF switches on
the roof panel. Power for the igniters is from the PE bus. An IGN ON annunciator on the roof panel illuminates whenever the ignition system is
operating in either the automatic (starting) or selective mode.
For Training Purpose Only. 74-00-00 5| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
For Training Purpose Only. 74-00-00 6| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
OPERATION
The ignition system operates in conjunction with the START PWR switch, the associated ENG 1 or ENG 2 starter switch, an HP leveroperated
microswitch, and the associated generator control unit (GCU). Automatic ignition is terminated by a 46% N2 speed sensor in the GCU which deenergizes the
start termination relay. The HP lever microswitch closes on engine start when the HP lever moves the power lever potentiometer through an angle of 6Q.
WARNING
The high-tension ignition system is lethal and may cause serious burns or death. A high-voltage charge may be stored for a period after the ignition is
turned off. Use extreme care when working on or near the ignition unit, high-tension cables, or igniter plugs.
Refer to Figure 74-3 for start control ignition switches.
Refer to Figures 74-4 for the No. 2 engine start schematic (with the ignition circuit energized). Figure 74-5 shows the engine ignition system in four
different conditions.
For Training Purpose Only. 74-00-00 7| P a g e
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ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
For Training Purpose Only. 74-00-00 8| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
For Training Purpose Only. 74-00-00 9| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
For Training Purpose Only. 74-00-00 10| P a g e
Jan 2024 ISSUE 01 REV 00
ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
For Training Purpose Only. 74-00-00 11| P a g e
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ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
For Training Purpose Only. 74-00-00 12| P a g e
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ATA 74 Hawker 750/800/800XP/850XP/900XP
IGNITION TRAINING MANUAL (B1/B2)
AUTOIGNITION
With ignition switches in AUTO, if there is uncommented deceleration of 500 rpm N1 for more than 0.2 seconds
and N2 deceleration of 70 rpm for more than 0.3 seconds, auto ignition occurs.
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