Yak-46's underwing engine alternative and for the Yak-42M, which was already 35-40% more efficient than the Yak-42. At the time, airline interest but no orders were reported for the Yak-46, but Yakovlev was negotiating to sell 200 Yak-42M planes to Aeroflot, which was then the world's largest airline. By October 1990, the two versions of the Yak-46 were in competition with the 102-126 seat Tupolev Tu-334, which like the higher-capacity Yak-46 had an interim turbofan version and a final propfan version, to replace hundreds of aging Tu-134 airliners at Aeroflot. To prepare for Yak-46 development, Yakovlev created a joint venture with Ivchenko Progress and the Soviet Ministry of Civil Aviation. Aeroflot would help fund a prototype, which would be built starting early in 1991 if the Yak-46 were selected. Annual production would eventually be as high as 100 airliners and would run through 2005. On March 15, 1991, Yakovlev finally began flight tests of one D-236 propfan engine on a Yak-42E-LL aircraft testbed, making it the first propfan flight test program led by an individual Soviet aircraft design bureau. The testbed appeared on static display at the 1991 Paris Air Show in June. Like the D-27 engine, the D-236 was a contra-rotating system with an eight-bladed front propeller and a six-bladed back propeller. It had a fan diameter of , a power rating of , and a thrust rating of . The testbed engine was limited to a smaller thrust, though, because the D-236 was more powerful than the Lotarev D-36 engine that it replaced. Meanwhile, conflicting reports appeared about the Yak-46 power plant: one article stated that the D-236 would be the eventual engine, but another article said Yakovlev was deciding between a gearless unducted fan, which would yield a fuel consumption of , and a less-efficient, but now considered more realistic, ducted fan with an ultra-high bypass ratio between 20 and 27. In August, a report stated that the initial version of the Yak-46, now named the Yak-46-1, would have two Progress underwing power plants resembling the International Aero Engines (IAE) SuperFan engine, while the follow-up version, called the Yak-46-2, would again be aft fuselage-mounted D-27 engines. A Soviet aviation publication named the initial engine as the Progress D-627, a quiet, super-high bypass ratio turbofan. Derived from the D-27, the D-627 had ducted, contra-rotating fans and used a differential gearbox. The D-627 had a takeoff thrust of ;