American Airlines was the first of the major US airlines to install a true premium economy seat, starting in October 2016. And now AA is about to be the first to complete its premium economy retrofits.On Tuesday evening, the final aircraft to get a premium economy retrofit, a Boeing 787-8 Dreamliner with registration N816AA, was ferried from Dallas/Fort Worth to Everett. In a couple of weeks, this aircraft should return to service to complete the international retrofit process.Courtesy of Flightradar24.comBut just by pulling this last un-retrofit aircraft from active service, American Airlines is reaching an important milestone: American Airlines has effectively harmonized its international fleet. From now on, passengers can know for sure what aircraft configuration they’ll be getting when booking an American Airlines aircraft.However, this milestone comes almost an entire year behind the original retrofit plan. In May 2017, American Airlines shared its premium economy retrofit schedule indicating that it’d finish the project by June 2018. At the time, I noted that this was a “very aggressive schedule,” which proved to be true.In December 2018, AA surpassed 100 aircraft with a premium economy cabin, leaving 19 of its 20 Boeing 787-8 Dreamliners left to retrofit. Now, more than five months later, AA is finishing its 788 retrofit.Still, American Airlines is years ahead of its direct rivals Delta and United; the latter just launched its international premium economy product on March 30. Once the installation process is complete, AA will have 124 aircraft in its international fleet with premium economy installed for a total of 3,025 premium economy seats:Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.AircraftFleetSeats per AircraftTotal Premium Economy seatsAirbus A330-2001521315Boeing 777-20047241,128Boeing 777-300ER2028560Boeing 787-82028560Boeing 787-92221462TOTAL1243,025Those are some pretty remarkable numbers. But it gets better. Another positive of American Airlines reaching this milestone is the certainty that passengers will now have about the arrangement of their aircraft. These premium economy retrofits served to harmonize the seating arrangements on AA’s international fleet.AircraftFleetVersionsFirstBizPEMCEEconomyTotalAirbus A330-200151202154152247Airbus A330-300912816247291Boeing 757-200 (int’l)2411652108176Boeing 757-200 (Hawaii)1011238138188Boeing 767-3002212821160209Boeing 777-200472372466146273Boeing 777-300ER2018522828188304Boeing 787-8201202848143239Boeing 787-9221302134200285Now, the only differences are on AA’s Boeing 757-200s and 777-200s – and the 757s will be harmonized by the end of 2019. Currently, American Airlines has a sub-fleet of 10 Boeing 757s that are mostly used for flights to/from Hawaii and only have recliner seats in business class. As American Airlines’ new A321neo aircraft are brought into the fleet, the 757s will be retired.That will only leave one aircraft with two different interior arrangements: the Boeing 777-200. While the 772s have been harmonized with the same number of seats in each cabin, the difference is between the types of seats in business class. Some 772s have solid B/E Aerospace Super Diamond seats while others have the “rocking chair” Zodiac Concept D seats.While AA’s domestic fleet remains frustratingly inconsistent, American Airlines flyers can celebrate getting certainty on the international fleet.