The Boeing 747-8 is currently the world's longest commercial jet in history with a fuselage measuring 250 ft 2 in (76.25 m), eclipsing the Airbus A340, which was 247 feet (75.30 meters) long.

The exact cost of the jumbo jet isn't clear, but a new 747-8 can fetch a cool $400 million. It's also unclear what it may cost to retrofit with necessary communications and security features.

Today, with hindsight being 20/20, we know how the Boeing 747 revolutionized air travel. But that was anything but a sure thing back when it was still on the drawing board in the mid-1960s.

Once United's farewell 747 flight touches down in Honolulu today, Delta will be the only U.S. carrier flying passengers in the jet. Delta's final 747 flight is scheduled for later this year.