The Federal Aviation Administration approved the folding wingtips of the coming Boeing 777X on May 18, 2018. The same day, Boeing announced that the wingtips entered the assembly line in Everett plant.

 

 

The retracting wings should allow the new version of the 777 to fit in the same airport stands as its predecessor. The folding tips give the 777X an additional 23 feet of wingspan, increasing the aircraft lift capacity. The $2 billion assembly line was specifically created for this new technology.

As no similar technology exists on a commercial aircraft, the FAA agency had to create airworthiness conditions from scratch. One of the criteria is to guarantee the folding mechanism cannot trigger during a flight.  However, folding wing technology is applied on military planes operating from aircraft carriers, such as the Boeing F/A-18E/F Super Hornet. The mechanism is a practical way to reduce the space needed for parking the planes in the tight hangar of a carrier.
 

An F/A-18F Super Hornet with folded wings aboard the USS Dwight D. Eisenhower (U.S. Navy)

The 777X body was delivered in March 2018, and its custom GE9X engine is already flight tested on a Boeing 747. The massive engine radius is as wide as the body of a McDonnell Douglas MD-90. The 777X will be the first twin-engine jet to be able to carry more than 400 passengers. It comes as a serious rival of two most spacious models of Airbus: A350 and A380. Nine airlines already showed interest for the new 777X, with a total of 326 planes ordered. First flight is expected for 2019, with deliveries starting in 2020.