Turbofan keeps running after pack is switched to off. 737-300/-400/-500

Sometimes the turbofan keeps running after the applicable packswitch is set to off and there is still bleed-pressure present in the duct. This is mostly caused by the packvalve and not the turbofan valve.  When the complaint is still there, remove the bleed-pressure and apply it back on, the valve will be closed and the turbofan will stop. So replacing the turbofanvalve will not help. It is often a stucked packvalve which is the troublemaker. It happens often after a long period of non-operation, for example a heavy maintenance visit.


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