Originally Posted by
goldstj2
UA uses a similar convention on ORD-BOS (520s through 540s) and ORD-LGA (668 through 694), to name two.
However, I know ORD-BOS isn't as consistent as DCA (there's an 881/882 thrown into the ORD-BOS schedule), and of course ORD-LGA has the much-loved Shuttle America flights interspersed throughout the day.
881/882 are extensions of ORD-NRT-ICN flights, which explains the 8XX numbers. Never knew you could go BOS-ORD-NRT-ICN on a single flight number. I've only been on the ORD-NRT-ICN part.