United Airlines flies IAH → LHR — 2 flight numbers on record (UA880, UA5). No departures are in the next-48h assignment window yet; aircraft assignments publish about two days out.
Counted from live tail assignments over the next 48 hours. A route with no equipped departures today can still get one — assignments publish about two days before departure.
Want the reverse leg? LHR to IAH, or compare a full itinerary.