Originally Posted by
woodenshoe101
That is not accurate.
It applies to European carriers at all times, but it also applies to non-European carriers on trips that depart from the EU. The fact that OP had a leg on both KL and DL on their ticket (and that KL was the original cause of the delay) is not relevant - when a EU261-qualified delay happens (on a single ticket with multiple carriers), you file with the operating carrier that got you to your final destination (DL may send the bill to KL for this one). If it had been a DL codeshare on a KL operated AMS-DTW, KL would have been the target to file with.
The EU261 applies to operating air carriers only. For example, you purchased your tickets from Lufthansa, an EU airline, for a flight to Europe from the United States. However, the operating air carrier is its codeshare partner, United Airlines. Since the flight is on a non-EU carrier and is terminating in the EU, it would not be covered under EU261. If your flight was operated by Lufthansa, regardless of whether you purchased your ticket from United Airlines or Lufthansa, your flight would qualify under EU261.
https://consumerrescue.org/guides/eu...e-europe-trip/
But I'm happy to be corrected, I do not live in the US and have only once in my lifetime used EU261
OP speaks about the RETURN trip, it's still a US originating flight on a non-eu airline. I do not know if that qualifies for EU261