American, Delta and Icelandair have Seattle to Frankfurt at $436 to $476 for travel October to December.
Icelandair is the lowest regular fare at $436, but fewest travel dates.
Delta low fares start at $476.
Travel dates for Frankfurt sale begin around October 22 through first week of December.
British Airways AARP ticket
Seattle SEA – London LHR – Frankfurt – London LHR – Seattle SEA
Seattle SEA – Atlanta ATL – Frankfurt FRA – New York JFK – Seattle SEA
Seattle SEA – Keflavik KEF – Frankfurt FRA – KEF – SEA
Icelandair can be ticketed with a stopover in Iceland for about $15 to $25 more.