Just had a very frustrating rebooking issue on another UA ticket gone completely sideways. Booked DCA-EWR-xxx.

DCA-EWR booked for 430pm. UA swaps aircraft in DCA so now the delayed 3pm (mechanical issue) uses the plane that I was supposed to be on at 430pm. So I grab a seat on the 300pm now departing 430pm while the 430pm gets rolling delays. We depart and sit on the tarmac for a 526 wheels up time. I hear the pilots try to start the second engine and no-go. So we get an overhead from the pilot that we're going to a different runway for takeoff and we'll be departing shortly. Riiiiiight. Sitting at the end of runway 1 we get told there's a electrical issue with this plane and we're going back to the gate. LSS...I was never going to make my connection in EWR now. I call the 1K line...

Me: Hi, I'm stuck in DC. The flight has now returned to the gate, it's an electrical problem, it'll be hours before it's fixed (if ever). I'm trying to get to xxx.
1K Line: Ok, let me look. <Typing, humming, typing> Sorry, sir. The AA flight is booked full.
Me: Ok, I saw that. But I also found availability on DL through ATL. Can you please put me on that?
1K Line: No, sir. I can't do that. You must be rebooked on Star Alliance carriers only. (Total bull as it's a mechanical issue and not weather related)
Me: <Gasps as I'm about to point out>....
1K Line: oh, and American. I can put you on American but not Delta.
Me: Huh? AA isn't *A. What's the difference?
1K Line: Sorry, sir. It's *A or AA only.

HUCA.

Next agent I get understands the issue and told me that he would need at least one hour lead time to rebook me on DL.

Longer story short...on the fly I had to change the airport I was flying to. UA put me on the AA non-stop to the new airport and rebooked my return to be out of that airport. No change in fare although if I had booked to this city originally it was $70 cheaper. I didn't ask for a refund.

It's been a long time since IROPS has forced a change in carrier but this is new if DL "is a no go" and then "requires at least one hour" while AA ticketed immediately.

And to close the loop...
The 3pm DCA-EWR that I wound up on and was delayed to 430p and then returned to the gate was never officially cancelled. They delayed it until 0630am the next day.
The 430pm DCA-EWR that I was originally booked on ultimately departed at 830pm. I would never have made my original connection or the later one.
The AA flight I took was delayed due to crew rest. Interesting that I have this happen all the time on United and they at least tell you when/where the crew is coming from. AA simply said we're delayed waiting for the crew with absolutely zero clue on when they might be coming.
As I boarded the AA flight (group 8), the FA was doing full PDB service. I had to laugh as UA refuses to do this on 99% of flights and the first thing I see on AA is open cart.

Oh, and both UA flights on my return were also delayed for mechanical issues.

-RM