First, there are the fuel lines, which deliver fuel from the fuel inlet to the fuel injectors. Fuel quantity control is typically achieved by the engine's fuel regulator. This regulator needs to sense the engine's status, requiring connections to various sensors for air pressure, temperature, engine speed, etc. Most sensors are electronic, but some are hydraulic, resulting in a complex network of lines.
Second, there are the lubrication system lines. The engine has several large bearings supporting the rotor's rotation, requiring constant lubrication. The accessory gearbox also needs lubrication, making the lubrication system's lines quite complex.
Third, there are the lines for air intake control actuators or valves. Engines have actuators that control the air intake, such as the VSV (Variable Stator Vane) control. The controller adjusts the stator vane angle based on the engine's status, usually hydraulically controlled, thus also requiring numerous lines.
Fourth, there are the air intake pipes. The front half of the engine generally has a lower temperature, while the rear half (behind the combustion chamber) has a higher temperature. Air needs to be drawn from the front half to the rear half for cooling. Therefore, there are many different cooling air pipes. There are also starter air pipes; aircraft engine starters are generally pneumatic. They require bleed air from the APU engine to rotate the core engine and complete the start-up and ignition.
Fifthly, there are various cables, including those for sensors, igniters, controllers, power supplies, and electronic communication lines with the aircraft.
