Leeds- New York
Probably no logistical reason why United or another carrier could not fly this route with a 757. There are economic reasons against it however. The main one being saturation - north of England to USA is a limited market already well-served out of MAN by several US majors. Saturating long-haul capacity across thin overlapping catchments usually ends in tears. Bristol couldn't be sustained against LHR. Leeds city region and most of its catchment is an hour or so from MAN, too close and overlapping to be viable for dedicated long-haul, even to New York.