Originally Posted by
estrela
The EU regulation would cover the next available flight IAD-MAN whatever airline this is.
No, if the OP was offered the next same day flight IST-MAN (despite a long layover) TAP is under no obligation to rebook the OP to other airlines. Had there been no same day departure to MAN, the OP would be entitled to rebook as you suggest. Anyway, TAP is never going to accept to rebook to other airlines so the discussion is mute.