2017, the business jet variant's additional fuel tanks were certified to carry 3,100 kg (6,800 lb) more fuel, increasing range from to . London City Airport is a major destination for Irish airline CityJet, which was to receive 15 SSJ100s, but its steep 5.5° approach required new control laws, wing flap setting and modified brakes: test flights were to begin in December 2017, with certification planned for 2018, and the modified aircraft to be available in 2019. A new "sabrelet" winglet, helping takeoff and landing performance and delivering 3% better fuel burn, will be standard and available for retrofit. Designed with CFD tools by Sukhoi and TsAGI, the "saberlets" debuted flight tests on 21 December 2017. They should improve hot and high airport performance and cut costs up to $70,000 per year. Parts of the wing are reinforced for the aerodynamic loads distribution change. They should reduce fuel costs by 4%, flight-testing was completed after over 140 flights by October 2019. The first aircraft with the composite winglets was delivered to Russian carrier Severstal Aircompany in December 2019. By November 2018, the TsAGI carried out wind tunnel tests on two modified wing designs to save structural weight: one with less wing sweep and the other with more relative thickness, also enhancing aerodynamics and load capabilities, and improving fuel efficiency by nearly 10%. Russified SSJ To resist the Airbus–Boeing duopoly pressure on regional jets through the Embraer E-Jet E2 and the Airbus A220, Sukhoi would upgrade the SSJ100 to the SSJ100B and the "Russianised" SSJ100R. Western content accounts for 55–60% of the original SSJ100's cost but sanctions against Russia are tightening. As of December 2018, the US authorities did not send any feedback to Sukhoi over exports to Iran. The SSJ100B would feature more powerful SaM146-1S18 engines, improved avionics software, enhanced high-lift devices controls and retrofittable "sabrelet" blended wingtip devices. After 2021 the SSJ100R would replace western components by Russian ones for government customers and countries subject to Western sanctions such as Iran Air Tours and Iran Aseman. SSJ100R could include a smaller variant of the Aviadvigatel PD-14 engine (Aviadvigatel PD-8); KRET electronic units to replace the Thales avionics; a Russian inertial navigation system and APU to replace Honeywell's; and the landing gear to replace one produced by Safran. Fuel burn would be reduced by 5–8% with a new composite wing. Russian content should double to 30% as US restrictions limit