Everett - Engineers and mechanics at the Everett plant are preparing the Boeing's new jetliner for its first flight. The 777X is expected to carry out its maiden flight next month.

The plane has two versions, the 777-8, and the longer variant 777-9. The first prototype is the 252,6 ft (77 meters) long 777-9. It has a wingspan of 236.2 ft (72 meters) including the 11.1 feet-long (3.4 meters) foldable wingtips.

The airframe of the first flying prototype has already been assembled. The primary systems are installed and powered for the first time. The first of two GE9X engines was fitted under the left wing, and the second will be installed in the coming days this month. General Electric's GE9X is the largest engine ever produced for a commercial aircraft.

Update: On January 4, Boeing announced on social media that they have completed the installation of both engines.

It is now being equipped with the wires and sensors that will send every data to the computers during test flights.

The 777X program seems already to be on track. There is no deviation from the original plan. The development of the two airframes for static testing and the four prototypes for flight testing has been in progress as planned.

Boeing's new widebody is intended to replace the 777-300ER, an aircraft that has long been Boeing's flagship widebody, and the backbone of the airlines' long-haul fleets around the world such as Emirates and Singapore Airlines.

The 777-9 has three additional rows of seats compared to 777-8 and will be able to carry 400 to 425 passengers. Although it is similar to the 777-300ER in weight, the 777-9 is more fuel efficient and has a flight range of 7500 nautical miles (14,000 km) thanks to its new GE-9X engines and the new foldable wings. On the ground, these slender wings are folded to fit the aircraft in the parking lots and boarding gates.

The $426 million list price of the 777-9 makes it Boeing's most expensive plane ever.

Boeing has already modified its production lines over the past two years to prepare for the 777X while avoiding to disrupt the production of the regular 777. Boeing engineers switch all the flexible equipment so that one line could be both used for both 777 and 777X production.

The wings of the first two aircraft that Boeing will deliver to customers, are already being assembled. Once the wings are ready, Boeing uses a new method to install wing systems including the wiring, the hydraulics, and the control surfaces. They are installed on the wings before the wing structure is attached to the plane, rather than after.

At this stage, almost all work is done manually. Engineers and mechanics perform complex jobs, such as assembling the trailing edges of the wings to ensure they are perfectly fitted to provide smooth airflow.

The first 777 was introduced to the market in 1994. The 777X will enter into service nearly 25 years after its predecessor. Since then, The Boeing 777 has become a real success story for Boeing. Emirates took delivery of its 190th and the last 777-300ER last month. The Dubai-based airline will also take delivery of its first 777X as the launch customer next year.

Emirates to receive its 190th Boeing 777-300ER

Boeing plans to persevere its dominance in the large widebody airliner segment with the 777X against the Airbus's all-composite, slightly smaller Airbus A350XWB.