There are essentialy two types of compressor stalls:
1) Stall on engine acceleration, often caused by a malfunctioning variable stator vane actuator. The LPC
accelerates and the VSVs don´t open to let more air into the HPC, resulting in a pressure buildup between the LPC
and HPC, causing a reversion of flow in the LPC
2) Stall on engine descelaration, often caused by a VBV malfunction.
HPC spools down faster (it doesn´t have the inertia of the big fan attached to it) and can´t digest the air coming from the LPC
. Normaly bleedvalves at the engine station 2.5 (between the LPC
and HPC) will open to let the excess air escape. If this doesn´t happen, same result as above.
Stall might also be caused by a low pressure in the intake, e.g. during ground runs.
we have to use a closed run up hangar for power runs due to noise reasons. A 757 is about the limit what this hangar permits, because it limits the air going into the engine (not enough volume in front of the engines). Once we were testing a 767 with GE
CF6-80 engines and had to stop it after some moderate stalls. Thisd is also the reason why you should turn an engine facing the wind for starting it in high winds.