Refer to figure.
EASA LO 021.11.02.02.17: State the conditions that are possible causes of stall and surge.
EASA LO 021.11.02.02.18: Describe the indications of stall and surge.

Jet engine compressor blades are aerofoils, and like any aerofoil, they can stall if the angle of attack exceeds the critical angle of attack. This is due to the adverse pressure gradient created the the compressor blades → their entire purpose is to increase the pressure in the direction of airflow.

When the compressor blades stall, the airflow becomes disrupted, and the mass flow rate of air through the engine decreases until the blades become un-stalled.

Turbulence can cause a reduction in the airflow entering the engine inlet, leading to compressor stall.

Because compressor stall leads to a reduction of air flow through the engine, we get the following signs that this is occurring:

• Reduced thrust
• High Exhaust Gas Temperature (EGT) because fuel continues to be pumped into the engine and burned
• Fluctuations in RPM and fuel flow
• Banging or popping sound from effected engine

Compressor stall can also be accompanied by engine surging, where the airflow becomes low enough that some forward flow occurs back through the compressor stage. This can lead to fluctuations in thrust and rpm.

Erroneous engine throttle inputs due to the turbulence. → INCORRECT.

• Rapid changes to thrust would be considered unnecessary in turbulence, as the aircraft's stability will ensure that although the airspeed may oscillate, it should do so around a stable value. However, incorrect thrust inputs should not lead to an abnormally high EGT.

Vibrations in the engine drive shafts due to the aeroplane being buffeted by the turbulence. → INCORRECT.

• This should not occur in turbulence. In any case, engine vibrations themselves should not lead to a high EGT - but high EGT and engine vibration together would be a sign of engine damage.

Engine compressor stall due to disrupted airflow into the engine intakes. → CORRECT.

• Heavy turbulence can lead to engine stall, and the fluctuating thrust/rpm and high EGT support this

Reduced cooling and lubrication to the engines due to the oil flow being disrupted. → INCORRECT.

• Oil flow should not be disrupted by turbulence. If there was a problem with oil flow through the engine, we would likely see other symptoms of this such as low oil pressure or high engine oil temperature, not described in the question.