To be fair Ryanair actually predate most full service carriers, Lufthansa's first route was to Munich which was in response to Go flying there, Frankfurt followed but Ryanair at this point already flew to Hahn - this was one of Ryanairs earliest non Stansted-Ireland routes. SAS have had a number of stints but again first Oslo was started in response to Color Air, Copenhagen to Go. At points in the late 90's/early 00's some routes had 3 carriers competing (e.g Frankfurt, Oslo, Glasgow) which was never going to last. 9/11 put pay to SAS and Lufthansa. I think what may prevent a Stansted return KLM now is a decent London City frequency, not just from KLM but from British Airways cityflyer. The same could be said for Gatwick, Transavia flew to Amsterdam for years but aside from British Airways (if we count them as full service) there is a few non low cost european carriers feeding a hub, Air Europa, Aer Lingus, TAP, Turkish come to mind
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