System and Components Flashcards
Main Components
Main Engine Control Unit (MEC)
Power Management Control (PMC)
Autothrottle
Thrust Reversers
Starting System
Ignition System
Oil System
Fuel System
Fire System
Low Pressure vs High Pressure
The two independent rotor systems inside the engine are the low and high pressure systems (N1, N2)
Low Pressure system includes a:
- Fan
- 3-Stage Booster
- 4-Stage Low Pressure Turbine
High Pressure system includes:
- 9-Stage Compressor
- Single-Rotor-Stage High Pressure Turbine
How Does the Engine Operate (Normally)?
Inlet air passes through the fan in the low pressure system then is split into two parts. Most of the air is exhausted through the fan duct (and reverser, if operating). The remaining air enters the booster stages and continues through the high pressure compressor to the burner and turbines. N2 turbine drives the accessory gearbox through reduction gears.
MEC Main Purpose
Main Engine Control Unit, governs core engine speed N2 by regulating the fuel flow to the engine, based on throttle or reverse lever position.
Controls the inlet guide vanes and the first three sets of stator vanes in the high pressure compressor, the variable bleed valves, and the high pressure turbine clearance control system.
Variable Bleed Valves Main Purpose
Regulate the bleed air between the booster and the compressor sections to prevent compressor stalls during engine acceleration and deceleration.
Can also open during reverse thrust to reduce reingestion of exhaust gases.
PMC Main Purpose
Power Management Control system sets the fan N1 Speed by trimming the MEC to maintain constant thrust as airspeed and altitude changes.
Powered by the control Alternator (N2 Tachometer generator)
Adjustments are made based on N1, fan inlet temperature, and static air pressure.
Do throttles need to be aligned to set the same N1?
No, there is a tolerance with the N1 Tachometers, throttle linkage, and variations in bleed air valve operations.
Should be aligned within one-half knob width when PMCs are on, N1 within +/-1 Percent
Autothrottles
Part of the flight guidance system, the computer is connected to a throttle servo for each throttle and a synchro and N1 sensor at each engine.
Thrust Reversers
Hydraulically operated (Utility), located on each fan nozzle. Core engine exhaust is not reversed.
Mechanically interlocked with the throttles so they cannot be operated until the throttles are in the idle position.
Interlocked with the landing gear squat switch to prevent in-flight deployment.
Starting System
Each engine has an air turbine starter mounted on the transfer gearbox.
Starter operates on low pressure air from the bleed air manifold.
Air for starting can come from the APU, another engine, or ground starting unit.
Ignition System
Two low energy ignition systems on each engine. Ignitor 1 operates the left ignitor and #2 the right.
Controlled by the start switches. Used for ground and flight starts as well as to prevent flameouts in turbulence, precipitation, or flight at high angles of attack.
Ignition is cut off automatically with the pull of the fire switch.
