One of the most anticipated roll-outs in recent aviation history will take place on March 13 when Boeing unveils its giant twin - the 777X. In a tweet, Boeing has just announced the date. Boeing is building two models of the 777X family: the 400-seat -9, which will be the first to roll out and the longer range -8, which can seat 350 passengers and has a range capability of more than 17,220 km. SEE Video 777X takes to the sky in Germany SEE Greenpoint’s luxury 777X interior.  The driving force behind the 777X is Emirates' President Sir Tim Clark, whose airline is the lead buyer with an order for 150. Sir Tim describes the 777X as “an absolute peach”. Key to his enthusiasm is the aircraft’s economics and greater space — it is 20 percent more efficient per seat than the industry’s long-time benchmark the 777-300ER and its cabin is wider with bigger windows. The Boeing 777X combines the best features of the current 777 with a longer fuselage, new engine and the composite wing design from the Boeing 787. The photo below shows three 777X aircraft in the main production bay and the first rollout aircraft in the adjacent bay. Other airlines that have ordered the 777X are Lufthansa, Etihad Airways, Qatar Airways, Singapore Airlines, Cathay Pacific Airways, All Nippon Airlines and last week British Airways. Downunder Qantas and Air New Zealand are also evaluating the 777X along with its arch-rival the A350-1000. Qantas’s competition, called “Project Sunrise” demands Sydney to London non-stop capability with 300 passengers. Both Airbus and Boeing say they can meet the airline’s demands or "close to it." Qantas plans to add underfloor bunks to the winner of its competition because on ultra-long-haul flights the aircraft will carry virtually no cargo, just passenger’s bags. Air New Zealand is going to accelerate the redesign of its interior offering at its Hangar 22 seating project after it decides on either the  Boeing 777X or A350 in April. Air NZ chief executive Christopher Luxon told AirlineRatings.com at the inaugural of the airline’s first service to Chicago last year that the airline had been bringing customers through to experience mock-up cabin spaces in an attempt to learn their thinking about space, storage, and privacy. “We’ve been running customers through a number of mock-ups that at this stage are quite primitive and quite conceptual but are giving them a feel about what they want to play back to us around that,” he said