The flight passenger rights stated in the EU regulation (EC) 261/2004 apply if you are leaving the EU with any airline, or arriving in the EU with an airline registered in the EU (or Iceland, Norway or Switzerland).
For example, this itinerary will work:
28th May at 13.00: London - New York (with United Airlines flight UA18)
The reversed trip will only work if the air carrier is registered in the EU, Iceland, Norway or Switzerland.
Ifdelayed helps all air passengers from all countries who have experienced delayed, cancelled or overbooked flights that are subject to this EU regulation. If you have any doubts or questions about your disrupted flight’s eligibility, the fastest way to check is to use the Ifdelayed eligibility check and enter your flight details here.