• China Airlines ordered nearly $12 billion worth of Boeing and Airbus widebody aircraft.
• The deal is worth about $7.4 billion to Boeing, with China Airlines as its newest 777X customer.
• Boeing is still trying to certify the now at least six year delayed 777X.

Boeing has added another customer to its 777X backlog as the planemaker continues to work toward certification of the long-delayed widebody.

Taiwanese carrier China Airlines announced a nearly $12 billion order for 10 Boeing 777Xs, 10 Airbus A350-1000s, and four 777X freighters on Friday.

This is the first order Boeing has secured for the 777X since Korean Air and Qatar Airways announced deals for the jet in July.

According to a filing, the order is worth about $7.4 billion to Boeing at list prices and is likely a sign of relief for the struggling planemaker and its delayed 777X — a setback that has already put Boeing at least $1 billion in the hole.

The yet-to-be-certified 777X, which will come in two passenger variants, was already five years behind schedule when a labor strike halted production for over seven weeks this fall and further pushed the timeline back to at least 2026.

Quality control and 777X design issues haven't helped. Boeing finally restarted production of its 767 and 777 models on Wednesday.

The 777X is designed as a more fuel-efficient replacement for the classic 777. Thanks to its longer wings, more powerful engines, and revolutionary folding wingtips, the 777-9 variant China Airlines bought is designed to fly up to 426 people across nearly 8,400 miles.

Along with the 787 Dreamliner, the potentially lucrative 777X is key to Boeing's reputational and financial recovery.

However, the 777X's delays have forced airlines to fly older jets for longer. It has also opened the door for Airbus to sell its readily available rival A350.

"Emirates has had to make significant and highly expensive amendments to our fleet programs as a result of Boeing's multiple contractual shortfalls," Emirates president Tim Clark told Business Insider in October after the latest 777X delay.

Emirates received its first A350 in November. It was initially supposed to follow the 777X but will now lead the airline's long-haul expansion.

China Airlines joins a dozen other global buyers, like Emirates, Qatar Airways, and British Airways. No US airline has ordered the 777X because its size and range don't fit into the business models.

Data from the manufacturers shows about 1,350 global orders for the A350 and about 500 for the 777X.