Originally Posted by mahasamatman
What aircraft type are you flying IAD-SFO? What time of day are you flying? Both of these have tremendous impact on upgrade chances.
You nailed it. ^
On this route, UA uses 319's, 320's, 757's and three-cabin 763's. Choosing flights on the latter two will greatly increase one's upgrade chances, assuming they have the flexibility...
I'm flying IAD-SFO next week Tuesday (17/10), and the flight is F7, on a 757. The next flight, a three-class 763 is F3 C5.