United Airlines retired its last Boeing 737 on Wednesday, sending it off with a cross-country trip that was a retirement flight for one of its longtime pilots, too.

Capt. Bob Russo piloted the plane from Washington to Chicago to Denver to Los Angeles on Wednesday, with a final leg to San Francisco. Russo said that as he piloted the plane across the country, air traffic controllers noted that it was the last United 737 flight.

"Most said they understand this is the last one, and we are sorry to see the airplane go, and it was our pleasure to help," he said during the stopover in Los Angeles.

United was an early customer of the 737, taking delivery of its first one in 1968. The plane that flew on Wednesday was delivered in 1988.

United began phasing out the decades-old planes last year as fuel prices spiked. Fuel prices have come back down somewhat since then, but United is still shrinking its fleet because demand is lower.

Russo, 59, grew up in Chicago, where United is now based.

"I was a teenager near Midway airport in Chicago and I saw the first 737s take off in 1968 out of Midway," he said. "Who would have known that 41 years later I'd be flying the last 737 flight for United?"

Russo flew 737s for much of his 31 years with the airline, and said he figured he would retire whenever United's 737s did.

Boeing has delivered more than 6,000 of the planes, and the newer versions remain popular with airlines.