more than 400 seats—whose orders have slowed in the mid-2010s, since there are widebody twinjets with similar range and greater fuel efficiency, giving airlines more flexibility at a lower upfront cost. Volga-Dnepr Airlines signed a memorandum of understanding (MoU) with Boeing for the purchase of 20 more 747-8Fs at the 2015 Paris Air Show. This acquisition was finalized at the 2016 Farnborough Airshow. On October 27, 2016, UPS Airlines announced an order for 14 747-8Fs with options for an additional 14. The 14 options were then converted to official orders on February 1, 2018. Deliveries are scheduled from 2017 through 2022. On September 7, 2017, it was reported that Turkish Airlines is in negotiations with Boeing for purchasing 8 747-8Is to strengthen its widebody fleet. In 2019, list-price unit cost of a 747-8I was US$418.4M and a 747-8F US$419.2M. By early 2019, the backlog and production rates were sufficient to sustain production until late 2022. On July 2, 2020, media reports stated that Boeing intends to end 747 production in 2022 after the 16 outstanding orders are built and delivered. The demand for four-engine airliners has been flat for several years, with most orders going to the freighter version. On January 12, 2021, Atlas Air ordered four additional 747-8Fs. These are to be the final four 747-8s built. The last aircraft, a 747-8F freighter for Atlas Air, rolled off the production line on December 6, 2022, and was delivered on January 31, 2023. Design The 747-8 is a development of the Boeing 747 that takes advantage of improvements in technology and aerodynamics. The two 747-8 variants feature a fuselage stretch of over the , bringing the total length to . The 747-8 is the world's longest currently-operational passenger airliner, surpassing the Airbus A340-600 by . With a maximum take-off weight of , the 747-8 is the heaviest aircraft, commercial or military, manufactured in the U.S. Compared to the preceding , the wing design was overhauled. The sweep and basic structure were retained, avoiding additional costs, but the revised airfoil is thicker and deeper. The new wing features single-slotted outboard flaps and double-slotted inboard flaps. The wing's trailing edge and raked tip are made of carbon-fiber composites. The increased wingspan makes the 747-8 a Category F size airplane rather than Category E size, similar to the Airbus A380. Raked wingtips, similar to the ones used on the 777-200LR, 777-300ER, and 787