And so passengers on the flight were decked in 1970s garb, including bell bottoms and period flight attendant uniforms.
On board, they got a 1970s-inspired menu and, undoubtedly, some retro music.
In the economy section, the menu included a mai tai, cold shrimp cocktail, braised boneless short ribs or grilled shoyu chicken and a sundae or parfait.
"It was a very nice party. Everyone was up in the aisles and there was a constant chatter, everyone sharing stories. It was really amazing," said passenger Brian Engleman.
United officials said the flight sold out in 90 minutes after it went on sale in September.
"I saw that it was available and I jumped on it very quickly and was able to get a seat," said passenger Jason Schwartz.
Because the iconic jumbo jet changed the air travel game decades ago, United says saying goodbye to the "Queen of the Skies" is bittersweet.
"So many of our customers and our employees have flown on this plane, have serviced this plane, and they've served customers on this plane. So today was both an exciting day for us and a sad day for us," said Jim Olson, United's senior vice president of communications.
"It was the easiest airplane I've ever flown. You'd step out and you'd look at that airplane and say -- 'Did I bring all of that with me?' It's such a huge airplane," said Warren Phelps, retired United captain.
United made its first Boeing 747 flight on June 26, 1970. The airline is transitioning its 747s with more fuel efficient aircraft.
"There's a whole new generation of aircraft that's more modern and the in-flight experience is up-leveled," said Olson.
Delta Airlines is now the last U.S. passenger carrier to use 747s, but plans to retire the aircraft from its fleet by the end of the year.