Boeing and General Electric are preparing the world’s largest engine for takeoff.

Earlier this week, the two companies mounted the gargantuan engine onto a Boeing 747-400 flying testbed in California, according to Aviation Daily. Test flights are scheduled to begin at the end of the year.

The gigantic engine will eventually be used on Boeing’s upcoming 777X aircraft.

The engine alone has been in development for more than five years — and those five years have been spent cramming in an impressive amount of technology.

The inside fans alone span 11 feet in diameter, and the outside measures 14.5 feet across. The engine is capable of producing 100,000 pounds of thrust.

Not only will the engine be the largest GE has ever built, it will also be the quietest and produce the lowest emissions. It boasts a host of other superlatives, including the thinnest fan blades, the most powerful compressor in aviation, and brand-new parts made from 3D printing.

The engines could be installed on the first 777X next year and Boeing hopes to test its first 777-9 aircraft (the first in the 777X series) in early 2019. The “mini jumbo” jet is predicted to enter service sometime in 2020.