Boeing has delayed the delivery of its first 777-9 jet, a variant of its new 777X aircraft, by another year, and deliveries are now expected to start in 2025.
The US plane maker on Wednesday announced a temporary pause in the jet’s production until 2023, to avoid inventory build-up.
Boeing earlier said it expected to win certification for the 777X by the end of 2023.
The 777X, which has both the 777-8 and 777-9 variants, has been in development since 2013 and was anticipated to be released for airline use in June 2020.
However, the plane has been beset by delays as Boeing addresses certification queries from US air safety regulators.
The "delivery of the first 777-9 airplane is now expected in 2025, based on an updated assessment of the time required to meet certification requirements", Boeing said on Wednesday, as it announced a first-quarter loss of more than $1.2 billion.
"To minimise inventory and the number of airplanes requiring change incorporation, we’re ... adjusting the 777-9 production rate ramp, including a temporary pause through 2023."
It said this adjustment will enable it to add 777 freighter capacity starting in late 2023.
The plane maker, however, stressed the 777X programme is "progressing well in development and testing".
"We remain confident in the 777 programme and our customers continue to see the value in its compelling economics and sustainability benefits," it said.
"Airplane programmes serve our market for several decades, and it is important we take the time now to position for long-term success."
The 777X programme has faced a longer certification process after scrutiny over the 737 Max model, which had two fatal crashes.
Boeing's biggest customer of the 777X is Dubai's Emirates airline, with 126 aircraft on order.
Emirates president Tim Clark suggested last year that further delays were possible, saying: "It's unlikely that we're going to get it before 2023 or probably even 2024 and there are all sorts of hoops that they have to go through with regards to certification, build and all the other various regulatory requirements."
The Boeing 777X is equipped with two GE 9X engines that are smaller than those on the older 777ER variant, enabling it to perform 12 per cent better on fuel consumption and 10 per cent lower on operating costs than its competition, according to the US plane maker.
Its features include folding wing tips, allowing for an extended span of seven metres to maximise fuel efficiency.
The 777-8 will seat between 350 and 375 passengers, while the bigger 777-9 variant can carry between 400 and 425 passengers, both in a two-class configuration.
The 777-9’s cabin also comes with more room. It is four inches wider than that of the 777-8 variant, even though it has the same exterior circumference as the older aircraft. Boeing has sculpted interior walls for additional space, all the way to back of the cabin.
The plane has the highest payload and the lowest fuel use, emissions and operating cost per tonne of any large freighter, according to Boeing. It will offer a 25 per cent improvement in fuel efficiency while reducing emissions and operating costs by the same magnitude.