evacuation (refrigeration system servicing). A procedure in servicing vapor-cycle cooling systems in which a vacuum pump is used to remove all of the air from the system. Evacuation removes all traces of water vapor that could condense out, freeze, and block the system.
evaporation. The physical change of state of a material from a liquid into a gas.
evaporative cooling. See steam cooling.
evaporator (air condition system component). The component in a vapor-cycle air conditioning system in which the refrigerant absorbs heat from the aircraft cabin.
The refrigerant in the evaporator coils is a liquid in the form of tiny droplets. Warm air from the cabin blows through the fins on the coils, and heat from this air is absorbed by the refrigerant, changing the droplets of liquid into a vapor. The heat used to make this change is taken from the air and as a result the air passing through the evaporator is cooled.
exceedance condition. A condition in which a parameter sensed by the EICAS exceeds the limits for which it is programmed. See EICAS.
exciter (electrical generator). A device used to generate DC electricity to produce electromagnetism in the field of an alternator or generator.
exclusive OR gate (logic gate). A digital logic device having two or more inputs and only one output. There is a logic high on the output when one and only one input has a logic high.

“Execute missed approach” (air traffic control instruction). An instruction issued to a pilot on an instrument approach, directing him to continue inbound to the missed-approach point and then to execute the missed-approach procedure, as described on the Instrument Approach Procedure Chart or as previously assigned by ATC.