Are there cheap flights to LHR to EWR?

Why do domestic airline flight numbers often change from day to day?

• A lot of the international and some domestic flight numbers are well-established. For example: BA 001 is LCY -> SNN -> JFK UA 930 is SFO -> LHR AA 001 is JFK -> LAX Domestically, things are often different, and the flight number refers to completely different flights from day to day. Some examples: UA 234 Dec 7: IAH -> EWR -> MCO Dec 8: CLE -> EWR -> BOS Dec 9: CLE -> EWR -> MCO Dec 10: CLE -> EWR -> MCO AA 345 Dec 7: DFW -> MIA Dec 8: LGA -> ORD Dec 9: LGA -> ORD Dec 10: LGA -> ORD What is the method to this madness?

• Answer:

  It only looks like madness when somebody (a) doesn't have the actual airline schedule or doesn't bother to display it, (b) doesn't know how to read and understand the real airline schedule, or (c) is only looking at one week's schedule or a part thereof.  Usually, it's because consumers are looking at flights from their local airport, which is trying to simplify the schedule for the poor consumer.  The real data is collected for the OAG (ex Official Airline Guide), which used to be a telephone-book-sized, frequently-modified, small-print book and is now available on-line only by subscription. Take your last example, from American Airlines. AA 345 Dec 7: DFW -> MIA Dec 8: LGA -> ORD Dec 9: LGA -> ORD Dec 10: LGA -> ORD The key to the pattern is the day of the week, not the date. December 7 is Saturday.  December 8 is Sunday. December 9 is Monday December 10 is Tuesday. AA 345 flies DFW -> MIA every Saturday, 2013-11-23 through 2014-03-01, using a Boeing 737-800. AA 345 flies LGA -> ORD daily except Saturday, 2013-11-22 through 2014-02-10, using a McDonnell Douglas MD-80. Source: http://info.flightmapper.net/flight/American_Airlines_AA_345 BTW, some international trunk flights' itinerary may also vary, probably only slightly, according to the day of the week.