Originally Posted by
rch4u
For the most part, LGA-IAD and LGA-ORD operate exclusive of each other. Only two aircraft pass through LGA from on their way to from one hub to another:
The morning UA 846 (IAD-LGA) aircraft continues to either DEN or ORD.
The evening UA 847 (LGA-IAD) aircraft originates in DEN or ORD.
Other than those two, aircraft turn from their hub points of origin. There's no stealing aircraft during irregular operations.
It makes sense to do it like this when you have multiple flights a day. The good thing is there are a lot of options to get to Chicago from the NY area or the DC area if there happen to be problems. Both AA and UA fly to ORD from DCA and IAD and CO flies to ORD from EWR.