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BLOCK 14 ENGINE ELECTRICAL SYSTEMS LECTURE

Reference Materials

  • FAA-H-8083-AMP
  • FAA Written Materials
  • FAA Oral Questions

Starter-Generator Systems

  • Power Sources:

    • Power can be supplied to the bus from two sources:
    • Battery Switch
    • External Power
    • Both power sources cannot be active on the bus simultaneously.

  • External Power Receptacle:

    • Mechanically operated switch prevents battery power from remaining on the bus when external power is supplied.
    • Opens the external power receptacle switch and the battery relay.

  • Operational Capabilities:

    • The system can operate using either a battery or external power source.
    • When external power is connected, the battery cannot be connected to the bus.

Normal Start Sequence

  • Engine Master Switch:

    • Closing this switch allows current to flow to:
    • Ignition Switch (Wire 23)
    • Power Lever Switch (Wire 12)
    • Power Lever Lock Switch (Wire 21)

  • Ignition Switch:

    • Once closed, it sends current to the ignition relay contactor (Wire 11).

  • Start Switch:

    • Setting the switch to "start" energizes:
    • Ignition Relay (Wire 10)
    • Starter Relay (Wire 8)

  • Starter Relay Activation:

    • When energized, current flows through the contactors to the coil of the undercurrent relay, energizing the starter-generator (Wires 9 and 30).

Troubleshooting

  • Failed Engine Rotation:

    • If the engine fails to rotate after the starter switch is engaged, a likely cause may be a defective starter relay.

  • Master Switch Configuration:

    • Turning on the master, battery, and ignition switches while advancing the power lever allows current to flow to various components:
    • Fuel Pump Switch
    • Start Switch
    • Power Lever Switch
    • Fuel Solenoid Valve
    • One side of the Ignition Relay Contactor.

Current Flow After Engine Start

  • With the power lever advanced, current flows through:

    • Power Lever Lock Release Switch (Wire 21) to unlock relay lock.
    • Power Lever Relay activations after closing activates:
    • Fuel Heater (Wires 3 and 25)
    • Opens Fuel Solenoid Valve (Wires 3 and 19).

  • Current Supply During Engine Rotation:

    • When engine rotation starts, current flows through the Emergency Stop Relay Circuit (Wire 5) and the Undercurrent Relay (Wire 6).

Hung Start Situation

  • Hung Start Definition:

    • A condition where the engine fails to reach sufficient speed to stop starter rotation.
    • May require the start-stop switch to be set to the stop position.

  • Effects of Broken Wires:

    • If Wire 8 is broken after engine rotation starts, the current would be supplied through Wire 5 and the Undercurrent Relay (Wire 6), allowing starting to continue normally.

Undercurrent Relay Functionality

  • Purpose:
    • The undercurrent relay disconnects power from the starter-generator and ignition once sufficient engine speed is reached.

Ignition System Components

  • Ignition Sequence:

    • If power is already applied and engine master is closed, current is sent to the ignition switch.
    • Ignition Switch continues providing current to:
    • Ignition Relay Contactor (Wire 11)
    • Ignition Exciters Test Switch (Wire 14).

  • Wire Issues:

    • Breaking either Wire 14 or 15 allows normal operation of igniters but not during testing.
    • Breaking Wire 10 or the ignition relay would impede operation during a start attempt but allow ignitors to function when tested.

Examples of Component Operations

  • Operational Scenarios:
    • Components may still operate normally under certain conditions despite malfunctions in connected wires:
    • Wires 14 or 15 may break yet allow igniters to function during start.
    • Wire 10 or ignition relay issues may allow igniters to operate during test but fail during start attempts.