CHICAGO -

Boeing has booked a big order for its planned 777X aircraft.

Hong Kong airline Cathay Pacific is buying 21 of the planes, which Boeing will build later this decade.

The 777X will be an updated version of Boeing's best-selling 777. That is Boeing's second-biggest plane, used by airlines for very long international flights. For the new version, Boeing plans to replace its aluminum wings with wings made from a lightweight, high-tech plastic, and make other improvements that will make the plane more fuel-efficient.

Boeing has booked orders for 259 of the planes, worth a total of $95 billion at list prices.

Boeing builds the current 777 in Everett, Wash., but it is still deciding where it will build the 777X.

Its shares rose $1.13 to $136.30 in morning trading.