GE90 - Boeing 777 Engine Start Procedure

Introduction

GE90: World's most powerful commercial jet engine
Boeing 777: Best-selling wide-body aircraft
Engine and airframe combination is an engineering marvel
Lecture focus: Building the engine from scratch and understanding components/functions

Two rotor shafts: High Pressure Shaft (N2) and Low Pressure Shaft (N1)
Stator and rotor form a single stage
N2 Shaft: 9 stages of high-pressure compressors, 2 stages of high-pressure turbine
N1 Shaft: 6 stages of low-pressure turbine, 4 stages of low-pressure compressors, massive fan ahead

Battery:
- Battery switch on: Provides power to start APU
APU (Auxiliary Power Unit):
- Rotate and release APU start switch
- APU generator online: Provides full electrical power
- APU generator switch on: EEC power
Fuel System:
- Left main tank selected: Two left tank pump switches on
- Two boost pumps: Transfer fuel to engine spar valve
Bleed Switch:
- Ensure in auto position

Pneumatic Pressure:
- Start valve receives pneumatic pressure
- Auto-start feature via EEC
- Turn engine start switch to start
- EEC commands start valve to open
- Pneumatic pressure to air starter
- Air starter drives accessories gearbox
Gearbox Components:
- Horizontal drive shaft connects to transfer gearbox
- Transfer gearbox changes axis of rotation
- Radial drive shaft rotates N2 shaft
Airflow and Rotation:
- Increased N2: Positive airflow through engine core
- Positive rotation of N1 shaft: Leads to fan rotation and bypass airflow

Fuel Control Switch:
- Opens spar valve, fuel rushes to main fuel pump
- Pump driven by gearbox: Increases fuel pressure
- Fuel travels to fuel-oil heat exchanger (heats fuel, cools engine oil)
- Filter screens fuel for debris
Hydromechanical Unit (HMU):
- Controls fuel to the engine for combustion
- Excess fuel bypassed back to the pump
- Waits for EEC command to open fuel shut-off valve
EEC and Ignition:
- EEC waits for N2 to reach 21% RPM
- Commands one of the two ignition exciters
- Ignition exciter: Converts input power to high voltage pulse for igniter plug
Combustion Process:
- At 21% N2, EEC sets up engine for combustion
- Fuel travels via fuel flow transmitter to HMU
- Fuel for combustion: Through manifolds, nozzles, to combustion chamber
- Swirlers ensure proper fuel-air mixture
Turbine Rotation and Thrust:
- High pressure turbine drives high pressure compressor
- Low pressure turbine drives low pressure compressor and fan
- Increases airflow and thrust

Idle Power:
- At 56% N2: EEC deactivates ignition system
- At 64% N2: EEC commands start valve to close
- Pneumatic pressure cutoff disables air starter
- Engine stabilizes at idle power
End of Procedure:
- EEC signals complete engine start
- Start switch latch returns to normal position