reduced the empty weight of the aircraft, while maintaining a similar maximum take-off weight to the Su-27M. While the Su-27M design had the avionics to give the aircraft the nominal designation as a multi-role fighter, flight tests with the Russian Air Force revealed difficulties in efficiently deploying the aircraft's armament. According to Aviation Week & Space Technology, air force pilots described weapons trials with the aircraft in Akhtubinsk and Lipetsk as a "negative experience", with a particular emphasis on the layout of the cockpit and its adverse impact on the workload of the single pilot. Designers, test pilots and avionics software specialists therefore worked together to redesign the cockpit and its attendant systems and improve the human-machine interface. The information management system of aircraft's avionics suite had been changed so that it now has two digital computers which process information from the flight- and weapons-control systems. The information is then displayed on two multi-function liquid crystal displays, which replaced the smaller multi-function cathode-ray tube displays found on the Su-27M. The pilot can also view critical flight information on the head-up display, and is equipped with Hands On Throttle-And-Stick (HOTAS) controls. The Su-35 employs the powerful N035 Irbis-E ("Snow Leopard") passive electronically scanned array (PESA) radar, which is a further development of the N011M radar that had been evaluated on Su-27M test-beds and constitutes the core of the Su-35's weapons-control system. It is capable of detecting an aerial target up to away, and can track thirty airborne targets and engage eight of them simultaneously; in addition, the multi-function radar is capable of providing high-resolution images of the ground using synthetic aperture mode. The aircraft is equipped with an OLS-35 optoelectronic targeting system ahead of the cockpit to provide other forms of tracking including infra-red search and track. For defences against enemy tracking, the Su-35 is equipped with the L175M Khibiny-M electronic countermeasure system, while engineers have applied radar-absorbent materials to the engine inlets and front stages of the engine compressor to halve the Su-35's frontal radar cross-section and minimise the detection range of enemy radars. The multi-role Su-35 can deploy air-to-air missiles of up to range, and can carry the heavy Oniks anti-ship cruise missile, as well as the multitude of air-to-ground weaponry. The Su-35 is powered by a pair of Saturn AL-41F1S turbofan engines, formerly known as izdeliye (Product) 117S. A highly upgraded variant of the AL-31F, the AL-41F1S is