A few months ago, we started to see United Express flights pop up on LGA-ORD and EWR-ORD. At least on LGA-ORD, they seemed to be placed "in between" the usual hourly flights that run 6am-8pm as part of the normal schedule.

However, on "special" travel days, the UX flights appear to be taking on the role of hourly flights. Tomorrow, Dec 24, on LGA-ORD for example:

Mainline: 6am, 7am, 8am, 9am ... 12pm, 1pm, 2pm, 3pm, 5pm
Express: 7:30am, 11am

There's a gap in mainline service from 9am until noon. There's no 10am flight at all, and a Shuttle America flight fills in for the 11am slot.

Tonight, at 7pm, one flight for tomorrow is already listed as canceled. Not surprisingly, it's the 11am UX flight.

We all know that UX flights are generally the first to be canceled and the last to make it out in irregular operations. Unfortunately for the passengers on the 11am UX flight, every other EWR-ORD and LGA-ORD flight on Dec 24 was already booked solid before their flight was canceled.

Obviously Dec 24 is not a typical travel day. But NYC-ORD isn't a typical route either. The only other route pairs I can think of with similar frequencies in United's network are DCA-ORD and SFO-LAX, and neither of those run any UX flights at all. I'm not sure what the reasoning behind this apparent experiment was, but I really hope the result is not a gradual replacement of mainline service on this route.