Lomapaseo, EPR engines have a bad habit of icing up the temperature portion of the inlet P2/T2 probe in ice crystal icing (the pressure is usually OK because there is a lot of heat applied - ~500 watts - but for obvious reason the T2 sensor needs to be separated from all that heat and ice crystals can foul it up). This can really foul up thrust setting with the EEC in "normal" mode because the inlet T2 will read right at freezing (0 deg. C) - well above the rating corner point at high altitude. As a result the EEC may calculate a max EPR below what's necessary for maintaining altitude/airspeed. So if inlet probe icing is suspected in ice crystal icing, the checklist says to select EPR engines to Alternate mode to restore proper thrust setting.