First, the pre-start check — Page 226, Lesson 296

Let's pick this up with the ground operations side of the engine, because this is where a lot of real-world damage actually starts. I want to walk you through what happens before start, during turbulence, and after shutdown — because each phase has its own specific threat to the compressor. First, the pre-start check. Before you even think about starting the engine, you must give particular attention to the area on the ground in front of the engine intakes. You're checking that it's free of loose stones and other debris. Why the ground in front? Because that's the suction zone — the intake will pull air, and anything loose in that area, straight into the compressor. This is especially important for wing-mounted engines, because their intake sits close to the ground. The closer the intake is to the ground, the more likely it is to pick up loose material. And it's no coincidence that aft body-mounted engines — engines mounted at the rear of the fuselage, with their intake above the fuselage — suffer much less with foreign object ingestion. Their intake is simply farther from the debris source. Now, in-flight turbulence. Heavy turbulence can do more than spill your coffee — it can seriously disrupt the airflow into the engines. The fix here is to use the operating handbook turbulence penetration speed, and the correct rpm, or Engine Pressure Ratio — EPR. EPR is the ratio of engine exhaust pressure to intake pressure, and it's your power setting reference. Using the right speed and the right power setting reduces the possibility of compressor malfunction. And it may also be prudent, or even a requirement, to activate the continuous ignition — that's the ignition system running continuously rather than just at start — to reduce the probability of engine flame out. Flame out is when the combustion process stops, and continuous ignition helps relight or prevent that. Now the big one: ground operations. The vast majority of compressor damage is caused by Foreign Object Damage — FOD. When debris gets into the compressor, it damages the blades. And here's the chain of consequences: damage to the compressor blades leads to changes in the geometry of the system. The blades are shaped precisely to manage airflow, and once that geometry changes, you get performance deterioration, then compressor stall, and even engine surge — which is a violent reversal of airflow through the engine. So to prevent this damage, it's essential that operators of gas turbine engines take precautions that preclude the entry of debris into the area of the ramp — the ramp being the apron area where aircraft are parked and serviced. And the pilot's part is to ensure, during external pre-flight checks, that the engine intakes are free from any such debris. But the responsibility doesn't end there. After flight, you fit intake and exhaust covers. These prevent two things: ingress of contaminants — dirt, moisture, anything that could get in — and windmilling. Windmilling is when airflow spins the fan or compressor blades while the engine is shut down, which can cause damage or wear. So the covers stop both the contamination and the unwanted rotation. So the full picture: before start, check the ground and the intakes. In turbulence, use the right speed and power, and consider continuous ignition. After flight, cover the intakes and exhaust. Every one of those steps is protecting the compressor from damage that leads to performance loss, stall, or surge.