Yakovlev Yak-40 Yak-40TL

The AI-25 made the Yak-40 possible and then held it back. It was noisy, thirsty, and the smoke from the centre engine earned the aircraft the nickname 'cigarette butt' among Soviet crews. When fuel prices rose, the German operator General Air watched fuel go from twelve to thirty-six per cent of its costs and went bankrupt. With more than a thousand airframes built and plenty of structural life left, new engines were the obvious way to extend the type's career.

The Yak-40TL was the most conservative of the proposals: keep the trijet layout and swap the AI-25s for Lycoming LF 507s, a Western turbofan of the same class with far lower fuel burn and noise. The result would have been a recognisable aeroplane with familiar procedures and limits, but one able to meet the noise rules that were beginning to close airports to first-generation Soviet jets.

More ambitious schemes were examined alongside it. The Yak-40L went to two LF507-1Ns and, in its original form, to a slightly swept wing; the Yak-40P added large nacelles projecting ahead of the wing. The programme was a joint effort between the Russian firm Skorost and Textron Lycoming, later Allied-Signal, in the climate of former-rival partnerships that followed the end of the Soviet Union.

None of the three proposals materialised. Certifying a 1960s Soviet airframe with Western engines cost more than the residual fleet was worth, in a Russian market with no money and a regional network in free fall. The idea survived the programme, though: two decades later the SibNIA institute picked it up on its own initiative with Honeywell TFE731 engines, and that time the aircraft flew.