Yakovlev Yak-42

Work on the Yak-42 began in 1972, when Aeroflot needed a medium-range airliner to replace the Tu-134. The first proposals described a straight-wing aircraft powered by two Soloviev D-30 turbofans, in effect an enlarged Yak-40, but they were dropped as uncompetitive against Western airliners with high-bypass turbofans. Yakovlev chose instead a trijet layout related to those of the Yak-40 and the Tu-154: two engines on either side of the rear fuselage, the third inside the fuselage with its intake at the root of the fin, and a T-tail. The engines were to be three Lotarev D-36 three-shaft turbofans, whose development had started in 1971, with flight testing from 1974 and series production from 1977. With them the Yak-42 became the first Soviet airliner powered by high-bypass turbofans, with a bypass ratio of 5.4.

The prototypes were built between 1974 and 1976 and used to compare two wings: the 11-degree sweep of the first aircraft and the 23-degree sweep of those that followed. The Smolensk plant completed the first example at the end of 1974 and it began flight testing in 1975. The more swept wing won, and the configuration chosen as the basis for series aircraft, now designated Yak-42, also had a fully swept T-tail. The public first saw it at the 1977 Paris Air Show at Le Bourget, the same year series production started. The first production aircraft had a clean wing leading edge with no moving surfaces and plain trailing-edge flaps; later aircraft gained leading-edge slats and slotted flaps.

The aircraft is an all-metal low-wing monoplane with a pressurised semi-monocoque fuselage of circular section, the same width as that of the Tu-154. Each D-36 produced 6,500 kgf (about 63.7 kN) of take-off thrust. No thrust reversers were fitted: with a landing speed of 200 to 205 km/h, close to that of a turboprop such as the An-24, spoilers and wheel brakes were enough to stop it on the landing run. An auxiliary power unit was also installed in the rear fuselage. The cabin was designed for 120 passengers six abreast, or 100 on local services with more room for carry-on luggage and coats, and the flight crew was two pilots. Two built-in airstairs, one under the rear fuselage like the Yak-40's and one forward on the port side, and two underfloor holds for baggage, cargo and mail let it work from airfields with little ground equipment. The initial version had a maximum take-off weight of 54,000 kg, and the airframe was designed for 30,000 one-hour flights. The horizontal stabiliser was trimmable in flight, a detail that would weigh heavily on its story.

The application for an airworthiness certificate was filed on 5 July 1976, and the certificate was granted, after the required testing, on 18 December 1980. Meanwhile the first production aircraft had been completed on 28 April 1978. The first scheduled service, Moscow to Krasnodar, flew on 22 December 1980, and the build-up was slow: only about ten aircraft were flying by mid-1981. The Smolensk plant assembled 11 aircraft between 1977 and 1981; the Saratov plant, which had started in 1978, then took over manufacture. The original 120-seat, three-plus-three cabin soon gave way to a mixed layout with a two-plus-two first class and 96 economy seats, 104 in all. In their first year of operation Aeroflot's Yak-42s carried around 200,000 passengers, mostly out of Moscow, although international services were also opened, from Leningrad to Helsinki and from Donetsk to Prague, for which the ML variant was prepared. An Aeroflot Yak-42 was shown at the 1981 Paris Air Show, and in 1982 the Yugoslav carrier Aviogenex announced an order for seven aircraft that never materialised.

On 28 June 1982 Aeroflot Flight 8641, a Yak-42 registered CCCP-42529, lost control, entered a dive and broke up in mid-air before crashing near Verbovichi, in the Naroulia District of the Byelorussian SSR, not far from Mazyr. The jackscrew driving the horizontal stabiliser had failed through fatigue caused by design flaws, and the tailplane came away. All 132 people on board were killed; it remains the deadliest accident involving a Yak-42 and the deadliest in Belarus. The disaster halted production and operation of the type for two years. The fleet stayed on the ground until the defect had been rectified, in October 1984 according to the English-language Wikipedia; the Russian one places the interruption between 1982 and 1984, and the Spanish one dates the return to service to 1985.

Back in service, in September 1986 an Aeroflot Yak-42 (CCCP-42536) being used for security forces training burned out after a thunderflash set the interior alight; there were no casualties. In 1988 series production of the Yak-42D began, with greater range and a higher maximum take-off weight, and it replaced the initial version on the assembly line.

The original version set the pattern the whole family kept: three high-bypass engines, built-in airstairs and room for a hundred-odd passengers on medium-range routes. It was also the first Soviet airliner with modern turbofans, and its manufacture came to be shared between Smolensk and Saratov.