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.