epitaxial layer (transistor construction). A layer of semiconductor material whose crystalline orientation is the same as that of the substrate on which it is grown.
epoxy. A flexible, thermosetting polyether resin that has wide application as a matrix for composite materials and as an adhesive that bonds many different types of materials. Epoxy is noted for its durability and chemical resistance.
epoxy primer. A two-component finishing material that is mixed and sprayed over a steel or aluminum alloy aircraft structure. Epoxy primer provides a tough, chemical-resistant covering for the metal to protect it from corrosion and to provide a good bond for a topcoat system.
Epoxy primers are not used in many of the high-volume production lines because of the time needed for them to cure properly.
epoxy resin. A flexible, thermosetting resin used as a chemical-resistant coating. Epoxy resins can be reinforced with fiberglass or filaments of boron or carbon to make high-strength structural materials.
EPR (engine pressure ratio). The pressure measurement used as an indication of the amount of thrust being developed by an axial-flow gas turbine engine. EPR is the ratio between the compressor inlet total pressure and the turbine discharge total pressure.

EPR rated engine (gas turbine engine rating). A gas turbine engine whose rated thrust is expressed in terms related to its engine pressure ratio (EPR).

EPS (engineered performance standards) (air traffic control). A mathematically derived runway capacity standard.
EPS’s are calculated for each airport on an individual basis and reflect that airport’s aircraft mix, operating procedures, runway layout, and specific weather conditions. EPS’s do not give consideration to staffing, experience levels, equipment outages, and in-trail restrictions as does the airport acceptance rate (AAR).