Trondheim rewards the patient traveler, and after a decade of routing through Scandinavia's back doors, I can tell you there's no nonstop shortcut: business class from Seattle to Trondheim always means a connection, typically through Copenhagen with SAS, Frankfurt with Lufthansa, or Amsterdam with KLM. Total journey time runs about 11.5 hours of flying, but the real story is the layover strategy. SAS offers the most geographically logical routing, its A330 or A350 business class cabins on the transatlantic leg feeding into a short SK hop up to Værnes airport, Trondheim's compact, walkable terminal that rewards travelers who've minimized connection stress upstream.
My preferred build is Seattle–Copenhagen on SAS's long-haul business product, with its Nordic-minimalist flat-bed seating and genuinely good Scandinavian-inspired dining, then a same-alliance SK regional connection north. Lufthansa routes work well too, particularly if you want a stopover in Frankfurt to sample the Lufthansa First Class Terminal on the outbound (available if ticketed correctly, even connecting to business), before continuing on a Lufthansa A320-family business class hop toward Scandinavia and onward to Trondheim. KLM via Amsterdam is the third solid option, with Schiphol's efficient transfer process and KLM's World Business Class 787 or A330 seating making for a smooth mid-journey reset. My insider tip: book the Copenhagen or Amsterdam connection with at least 90 minutes buffer in summer, when Trondheim's airport sees a noticeable uptick in fjord-cruise-adjacent traffic that can slow immigration lines unexpectedly.
Seasonality matters enormously here. May through September is both the best weather window for Trondheim's fjords and midnight sun, and the sweet spot for business class award and revenue deals, as airlines compete for premium leisure demand before Norway's shoulder season quiets down. Given how fare buckets on these Scandinavian and connecting European routings fluctuate week to week, I'd strongly recommend setting up automated fare alerts rather than checking manually — the best business class fares on this route tend to surface briefly and disappear fast.
