The new Boeing 777X jetliner, the largest twin-engine jet in the world, has recently completed its first two flights successfully entering the next phase of rigorous tests as it awaits regulatory approval.

The American planemaker said the first flight took off at Paine Field in Everett, Washington, for a three hour, 51 minute flight over Washington state before landing at Seattle's Boeing Field, while a second test flight occured on January 29 for 4 hours and 45 minutes from Boeing Field, according to reports.

The Boeing 777X builds off of the popular Boeing 777 product line offering greater capacity and efficiency aided by new engines. 

"The 777X flew beautifully, and today's testing was very productive," said Capt. Van Chaney, 777/777X chief pilot for Boeing Test & Evaluation. "Thank you to all the teams who made today possible. I can't wait to go fly your airplane again."

Capt. Chaney and Boeing Chief Pilot Craig Bomben worked through a detailed test plan to exercise the airplane's systems and structures while the test team in Seattle monitored the data in real time.

"Our Boeing team has taken the most successful twin-aisle jet of all time and made it even more efficient, more capable and more comfortable for all," said Stan Deal, president and CEO of Boeing Commercial Airplanes. "Today's safe first flight of the 777X is a tribute to the years of hard work and dedication from our teammates, our suppliers and our community partners in Washington state and across the globe."

The first of four dedicated 777-9 flight test airplanes, WH001 will now undergo checks before resuming testing in the coming days. The test fleet, which began ground testing in Everett last year, will endure a comprehensive series of tests and conditions on the ground and in the air over the coming months to demonstrate the safety and reliability of the design.

The newest member of Boeing's market-leading widebody family, the 777X will deliver 10% lower fuel use and emissions and 10% lower operating costs than the competition through advanced aerodynamics, the latest generation carbon-fiber composite wing and the most advanced commercial engine ever built, GE Aviation's GE9X.

The new 777X also combines the best of the passenger-preferred 777 and 787 Dreamliner cabins with new innovations to deliver the flight experience of the future.

Boeing said it expects to deliver the first 777X in 2021. The program has  so far won 340 orders and commitments from leading carriers around the world, including ANA, British Airways, Cathay Pacific Airways, Emirates, Etihad Airways, Lufthansa, Qatar Airways and Singapore Airlines.

The 777X is the latest new aircraft of Boeing to fly since the grounding of the 737 MAX.