General Electric had been expected to start flight trials for the E9X engine in December (Reuters)

General Electric has begun flight trials of the world's largest jet engine after delays caused by technical problems, the U.S. conglomerate said on Wednesday.A special Boeing 747 test aircraft flew on Tuesday from Victorville, California, with the new E9X engine mounted under its left wing, dwarfing the plane's three other engines.The huge powerplant - as wide and tall as the fuselage of a Boeing 737 - is being built for the latest version of Boeing Co's long-haul 777, the 777X, which is due to enter service in 2020.During Tuesday's flight, engineers completed their test list and ensured key characteristics were working properly, GE said in a statement confirming the flight, reported earlier by Reuters.The flight marks the beginning of a flight-test campaign scheduled to last several months, before the aircraft itself takes to the skies in the first quarter of next year.GE had been expected to start flight trials in December, but announced in February it had found technical problems with both the engine and the test plane during preparatory work.The engine glitch will require the redesign of a part in the compressor, which is near the front of the engine and does not handle the hottest air flows.Despite the delay, GE feels "very confident" it will meet a 2019 target date for safety certification, a spokeswoman said.

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GE's partners on the engine include France's Safran, Japan's IHI Corp and Germany's MTU Aero Engines.