The Antonov An-10 Ukraina (; NATO reporting name: Cat) is a four-engined turboprop passenger transport aircraft designed in the Soviet Union. Design and development Development of a four-engined airliner intended for use on routes from began at the end of 1955. Inspired by the Izdeliye N (Izdeliye – article or product) passenger version of the Antonov An-8, the Antonov design bureau developed the Izdeliye U ("U" for "Universal"), a four-engined aircraft with a similar layout to the An-8, but with increased dimensions and a circular-section pressurised fuselage. Early in the design process the choice of engines was between the Kuznetsov NK-4 and the Ivchenko AI-20, and despite superior performance the Kuznetsov NK-4 was eliminated and the Ivchenko AI-20 selected, partly due to the Central Committee of the Communist Party of Ukraine which wanted as much as possible produced in Ukraine, where the Ivchenko factory was. The first prototype flew on 7 March 1957, revealing poor directional stability which led to a taller vertical fin, and later to hexagonal auxiliary fins at the tips of the tailplane. Entering production at Zavod (factory) No.64, Voronezh in 1957, the initial three aircraft were delivered with Kuznetsov NK-4 engines, due to non-availability of the Ivchenko AI-20 engines. From 1958, production aircraft were delivered with the Ivchenko AI-20A engines which boasted a longer service life and comparable performance compared to the Kuznetsov engines. The new aircraft was displayed to the public for the first time in July 1957; the design was approved for mass production after testing was completed in June 1959. Aeroflot began operations with the An-10 from 22 July 1959 on the Moscow – Simferopol route. Configured with 85 seats, the cabin was spacious and well-appointed with comfortable seats widely spaced, giving plenty of legroom, but due to the low cabin floor and wide diameter, there was much unusable space which limited baggage and cargo volume. The inefficient use of cabin volume contributed greatly to the low payload/TOW ratio which was much lower than that of the contemporary Ilyushin Il-18, but which was still higher than the Tupolev Tu-104. A later production version, the An-10A, addressed some of the efficiency concerns by increasing the number of seats from 85 to 89 and 100 (in the two versions of the An-10A), then to 117–118 and finally 132 through reducing seat pitch and changing the cabin layout. Powered by Ivchenko AI-20K engines the An-10A demonstrated