Boeing says it has reached a configuration milestone and can now move into the detailed design stage for the 777-9X.

The 777-9X adds a longer, composite wing and General Electric GE9X turbofan engines, folding wing-tips and a stretched and updated fuselage to the current 777-300ER.

According to Boeing, the 777-9X’s wing area will be almost 20% larger and more flexible than the current version.

In the detailed design phase, Boeing's development team will focus on the aircraft at the part and assembly level, as well as all of the electronic, hydraulic, and pneumatic systems. Boeing will launch the production phase as the detailed design phase nears completion. The first 777-9X test aircraft is scheduled to fly in 2018, and will enter service in 2020.