Soviet design bureau Yakovlev is developing a family of derivatives of the Yak-42 tri-jet airliner with significantly improved payload, range and fuel-efficiency, for entry into Aeroflot service from 1994.

The derivative aircraft, using turbofan, ducted and unducted propfan powerplants, are designed to comply with US FAR Part 25 airworthiness regulations and, if offered for export to the West as planned, would pose new competition in the medium-range 150- to 170-seat market.

The first derivative to fly will be theYak-42M, a re-engined Yak-42 with supercritical-section wing, winglets, 'glass' cockpit and fly-by-wire flight controls. The aircraft will be capable of carrying up to 168 passengers, according to Vladimir Dmitriev, deputy chief designer at Yakovlev.

The Yak-42M will be followed by a more advanced derivative, the Yak-46. This will share many technical features of the Yak-42M but dispenses with its three turbofans in favour of two propfan engines to give a further improvement in fuel efficiency over the basic Yak-42 now in service.

An intermediate derivative with wing-mounted ducted propfan engines to bridge the gap between the Yak-42M and the Yak-46 may also be developed.

PROPFAN CONFIDENCE

The emergence of these new designs is doubly significant. Firstly, it signals continuing Soviet confidence in the propfan concept -shelved in the West, because of low fuel prices - with Yakovlev now the second Soviet bureau designing a propfan-powered airliner (Tupolev was first). A tractor version of the pusher-propfan engine to be used was run for the first time last month and is a production prototype, not merely an experimental engine, according to Yakovlev.

Secondly, it puts Yakovlev in the running to join the exclusive international club of design teams with digital fly-by-wire aircraft, today's icon of high-technology civil aviation. Only fellow Soviet bureaux Tupolev and Ilyushin, along with the West's Airbus Industrie, have fly-by-wire airliners flying.

The original Yak-42 entered service with Aeroflot in 1980, and typically carries 120 passengers in a tourist layout over sectors of up to 1,700km (1,030nm) although it can carry...