Interesting! The aircraft from BRU would have been ours to LHR (thats what I read from the UA page flight status page beforehand) that night as we were meant to fly out of IAD. The flight was scheduled for 10pm departure and all looked good. We were at the UA Club in concourse C when at around 7.20pm the flight was cancelled.

At the UA desk within the lounge they mentioned due to maintenance and quickly rebooked us on UA to FRA and LH to LHR. The flight to FRA was then quite full, but not fully booked. We got "upgraded" to Eco Plus as well, which was a nice to have. The flight to LHR was then in Eco, booking class Y.

Wondering what would have been less expensive for UA, leaving us overnight in a hotel at IAD and catch another UA direct to LHR or rebook us via FRA and then FRA-LHR in Eco Y.

Anyway big thank you to UA as all our 6 suitcases made the connection as well. Great job UA !!

Btw, I prefer maintenance issue on ground over the ones in flight