Originally Posted by emcampbe

There may be additional factors that limit the use of some flight numbers as well. For example, unless something has changed, there used to be no flight numbers ending in 13. So that can take a whole wack of numbers out of the system. Also, not sure how the China flights are numbered, but I doubt they'd risk using something with a 4 in it since the Chinese generally consider it a bad luck number. So if they are trying to sequence flight numbers into PEK/PVG, there's another that might not get used.