Yakovlev Yak-40TL

The Yak-40 first flew on 21 October 1966 and was built at the Saratov Aviation Plant from 1967 to 1981. It was the first Soviet-built airliner designed to Western airworthiness requirements, and more than a thousand left the factory. It was powered by three Ivchenko AI-25 turbofans of 1500 kgf each, two on pylons on either side of the rear fuselage and the third inside the tail. When the Soviet Union came apart, a fleet of that size, with a design already shaped by Western rules and exported to countries such as Germany and Italy, made re-engining with Western turbofans an obvious idea. The Yak-40TL was one of the projects born from it, and it never left the drawing board.

The available account names the well-known American engine maker Textron Lycoming as the firm behind the project. Lycoming had announced its LF500 family of geared turbofans in September 1988, beginning with the LF507-1H, which was certificated in October 1991; the family descended from the ALF 502 that powered the British Aerospace 146 and later the Avro RJ. The turbofan line later passed through AlliedSignal to Honeywell; the Russian account dates the sale of that part of Lycoming's business to Honeywell to 1999, which is why the engine is now usually catalogued as the Honeywell LF507.

According to the Russian account, the calculations showed that the ideal solution was to replace the three AI-25s with two LF507-1Hs, engines similar to those of the BAe 146. The pair would burn as much fuel as the three Soviet engines but deliver a third more thrust. With a swept wing, the aircraft could realistically cruise at Mach 0.74, and maximum take-off weight could rise by a quarter. The same author, sketching his own idea of a reborn Yak-40, describes a swept wing with a supercritical profile and two engines of about three tonnes of thrust each, and presents the TL as the precedent for that approach.

The sources do not agree. The English-language variant list, based on Yefim Gordon, Dmitry and Sergey Komissarov's book OKB Yakovlev (Midland Publishing, 2005), describes the Yak-40TL as a proposed upgraded version to be powered by three Lycoming LF 507 turbofans, and assigns the twin-engined layout, with LF507-1N engines and a slightly swept wing, to a different designation: the Yak-40L, a joint programme between Skorost and Textron Lycoming. Military Factory contradicts itself: its narrative gives the TL three AI-25T engines, while its variant list gives it three LF507s. The Russian account, for its part, describes the TL with two LF507-1Hs and a swept wing, which is exactly what the other sources attribute to the Yak-40L. The two designations may refer to stages of the same Lycoming study, but no available source confirms it, so this page records the disagreement rather than resolving it. The Russian-language Wikipedia, the richest source on Yak-40 sub-variants, does not mention the TL at all.

Where all the sources agree is on the outcome: the Yak-40TL remained a project. The Russian account says it did not survive the 1990s, like many others of the period, and that it is rarely remembered today. None of the sources consulted gives a date for the start or end of the work, or mentions a prototype, a registration or a flight.

Replacing the three AI-25s with two modern engines did not die with it. In 2012 the SibNIA research institute in Novosibirsk began, on its own initiative, to re-engine a Yak-40 with Garrett TFE731 engines, replacing first one and later two; that work produced the Yak-40MS and, later, the STR-40DT with a composite wing, on which SibNIA completed work in July 2019. Those aircraft have their own pages; the TL is their unbuilt forerunner from the Lycoming era.