I'm searching for flight tickets to fly to Xi'an from London. Geographically, Xi'an is closer to London compared to Beijing to London. However, it takes less than 10 hours to fly to Beijing while almost 11 hours to fly to Xi'an. Does anyone know why?
As Nate Eldredge points out, the distances are about the same. It doesn't look like that on a conventional world map in cylindrical projection, but is less surprising if you look at a polar projection instead.
Some of the difference in scheduled flight times is due to different aircraft. The single route from London to Xian is GS 7988 which seems to be timetabled for an Airbus A330, while the fastest flights to Peking are flown with A350 and Boeing 777, which have a slightly faster most efficient speed.
However, there's a daily flight LHR-PEK with an A330, CA 788. This is timetabled to take 10h15, compared to 10h50 for GS 7988. It looks like this is just a matter of Tianjin Airlines being more conservative in their scheduling than Air China is. In the flight history currently visible on Flightradar24 it looks like GS 7988 routinely arrives up to an hour early, whereas CA 788 typically arrives about half an hour early when departs London on time.
So the actual airborne time is about the same, but Tianjin Airlines has more of a buffer before they need to pay delay compensation.