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System Description
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(WARNING)
RED MESSAGE (CAUTION)
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WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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01/07/16

Overview

The function of the electrical power supply is to supply a very high voltage for an ignition of the fuel/air mixture in the combustion section.

Each engine has a dual-channel ignition system. Each ignition system has an ignition unit. The aircraft power sends a 28 VDC input voltage to the ignition unit. The ignition unit changes this 28 VDC input voltage to an 8 to 14 kVDC output voltage. This high voltage is sent through the ignition leads to give the sparks at the ignition plug tips at a rate of three sparks each second (0.5 joules each spark).

01/07/16

Ignition Unit

The ignition unit is installed at the bottom on the rear outer fan duct. The ignition unit is a dual-channel, capacitive discharge unit with three electrical connections. One connection is for a 28 VDC power input from the aircraft electrical bus through the engine control unit (ECU). The other two connections are for the outputs to the two ignition leads. The two channels in the ignition unit operates independently from each other. Each channel supplies the output voltage to its own ignition lead.

The ignition unit operates as an electrical power supply for the ignition system. The ignition unit has an internal power transformer to increase the low input dc voltage to a high output DC voltage. This high output DC voltage is necessary to start the sparks for an ignition of the engine.

Operation

The dual-channel ignition unit operates as the power supply for the ignition system. It receives its 28 VDC power from the aircraft through the ECU. The ignition unit changes the 28 VDC input voltage into a 8 to 14 KV output voltage that has a pulse. A power transformer in the ignition unit increases this voltage and supplies it to the unit's discharge section.

In the discharge section, a capacitor collects this voltage until it gets to the capacitor's voltage limit. The capacitor then releases this energy at a rate of three pulses for each second, through the two ignition leads. Two ignition plugs receive these pulses to make the electrical sparks.

01/07/16

System Interface

The power supply system has the interfaces with the component and system that follow:

  • Engine Control Units (ECU)
  • Ignition System

10/22/20

Component Location Index

Component Location Index
IDENT DESCRIPTION LOCATION IPC REF
     - IGNITION UNIT (LH)  ZONE(S) 432BB 74-10-01
     - IGNITION UNIT (RH) ZONE(S) 442BB 74-10-01

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