Western and then Delta used to fly jets out of DCA which first stopped at IAD before heading out to SLC. Did the same on the way back, I think to avoid the limitations on the length of flights for planes out of DCA at the time. Flew that flight dozens of times headed from DCA out to SLC or various other locations in the intermountain West during the 80's, back when I was a federal prosecutor based in DC.

Djlawman