Join Date: Jun 2001
Location: The road less traveled
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EconomyPlus is not technically a separate class of service. HOWEVER, you must purchase a full-fare economy ticket or hold elite status with United to pre-reserve a seat in EconomyPlus.
When you get to the airport, you can request an EconomyPlus at check-in and/or at the gate. (Sometimes EasyCheck-in Machines will offer to sell you a seat in EconomyPlus when you check-in for $25 or so.)
What equipment does United fly to GEG? If they are flights operated by United Express, then they will not have EconomyPlus.