Яковлев Як-42: Советский ближне-среднемагистральный авиалайнер

Soviet mid range jet airliner

{|Infobox aircraft type
|type = Narrow body airliner
|design group = Yakovlev
|builder = Saratov Aviation Plant
|first flight = 7 March 1975
|introduction = 22 December 1980
|retired =
|status = In service
|primary user = Izhavia
|more users = Jet Express AirlinesKosmos AirlinesKrasAviaRusJet
|produced = 1977–2003
|number built = 187

In 1972, the Yakovlev design bureau started work on a short to medium range airliner capable of carrying 100–120 passengers. It was intended to be a replacement for the Tupolev Tu 134 jet as well as the Ilyushin Il 18, Antonov An 24 and An 26 turboprop airliners. While the new airliner was required to operate out of relatively small airfields while maintaining good economy, as many Soviet airports had been upgraded to accommodate more advanced aircraft, it did not have to have the same ability to operate from grass strips as Yakovlev's smaller Yak 40. The requirement resulted in the largest, heaviest and most powerful aircraft designed by Yakovlev, until the even larger MC 21 took flight in 2017. Initial design proposals included a straight wing airliner powered by two Soloviev D 30 turbofans and resembling an enlarged Yak 40, but this was rejected as it was considered uncompetitive compared to Western airliners powered by high bypass ratio turbofans. Yakovlev settled on a design powered by three of the new Lotarev D 36 three shaft high bypass turbofans, which were to provide 63.90 kN (14,330 lbf) of thrust. Unlike the Yak 40, the new airliner would have swept wings. The first of three prototypes, which was fitted with an 11 degree wing and registered SSSR 1974, made its maiden flight on 7 March 1975. It was followed by the second prototype, (SSSR 1975) with the 23 degree wing and a cabin with 20 rows of windows instead of 17 in the first prototype, and a third prototype (SSSR 1976) fitted with improved de icing gear.

The Yak 42 is a low winged monoplane of all metal construction, with a design lifespan of 30,000 one hour flights. All of the prototypes had main landing gear with two wheels each, with the first serial production aircraft, four main wheels were introduced. The wing layout underwent considerable revision during the design process, with the first prototype being built with a wing sweep of 11 degrees and the second prototype with a sweep of 23 degrees. After evaluation, the greater sweep of the second prototype was chosen for production. Early aircraft had a clean wing leading edge with no control surfaces, and plain trailing edge flaps. This changed in later aircraft, which were fitted with leading edge slats, with the trailing edge flaps slotted. Two engines were mounted in pods on either side of the rear fuselage, with the third embedded inside the rear fuselage, fed with air via an "S duct" air inlet. An auxiliary power unit (APU) is also fitted in the rear fuselage. No thrust reversers are fitted. The aircraft has a T tail, with both the vertical fin and the horizontal surfaces swept. In its first year of operation Aeroflot's Yak 42s carried about 200,000 passengers, mainly on routes from Moscow, but also on international services from Leningrad to Helsinki and from Donetsk to Prague, with the type being planned to enter wider service throughout the Aeroflot fleet. On 28 June 1982, however, the tailplane detached from an Aeroflot Yak 42 in flight owing to a failure of the actuator screw jack, causing the aircraft to fatally crash near Mazyr. The type was grounded as a result, not returning to service until October 1984. An export order for seven aircraft was announced in 1982 by Aviogenex of Yugoslavia, but the contract lapsed. As of 1 January 1995 a total of 185 Yak 42 had been produced, including 105 Yak 42Ds.

As of July 2019, 22 Yak 42s remained in commercial airline service. Operators are Izhavia (8), KrasAvia (10) and Turukhan Airlines (4).