The heaviest fighter plane able to hover is Lockheed Martin's F-35 Joint Strike Fighter which has an empty weight of 27,000 lb (12,250 kg) and has a maximum take off weight of over 50,000 lb (22,700 kg). The first flight of the Lockheed Martin F-35 was on 24 October 2000 and features a vertically mounted 'lift fan' behind the cockpit, driven by a shaft off the engine, plus a vectored exhaust and two exhaust ducts, extending from each side of the engine to exit in the bottom of the wings. The lift fan minimizes hot exhaust ingestion back into the engine and provides up to 8,150 kg (80.1 kN/18,000 lb) of lift thrust. Each F-35 has about 5 million lines of software and has a combat range of 600 nautical miles (1,100 km). Lockheed Martin expects to build 3,000 JSFs with low-rate initial production to start in late 2006.