Airbus has indicated a schedule slip for A350 development, no longer identifying the third quarter of 2011 as the date for commencing final assembly, instead stating only that it will begin before the end of the year.
But the company is still pushing for a mid-2012 first flight, even as it maintains that this will need a nine-month assembly lead time.
The manufacturer had previously said it would begin final assembly in the third quarter of this year.
But during Airbus' annual briefing in Toulouse, chief operating officer Fabrice Bregier said the airframer would start assembly of the first A350's main components "around mid-year" and that it would be "ready for the final assembly line before the end of 2011".
Bregier says Airbus is still planning to allow around nine months for assembly and tests, and that the A350 would have undergone close to 18 months of tests by the time of its maiden flight - after which it would be subjected to another 12 months of flight testing.
Delivery of the first aircraft, he adds, will be in the second half of 2013. Late last year Airbus parent EADS had warned that the delivery would be pushed back from the early part of the second half, stating that the design-to-manufacturing transition was taking longer than expected.
Bregier says the airframer is "still very humble about this programme", that the manufacturer is making "reasonable progress" on the A350 but that the aircraft's development remains "very challenging".
He says processes which did "not perfectly fit on the A380" - in a range of areas, including system installation and customisation - are being changed on the A350.
"One lesson [learned from the A380] - when you're not ready, you don't move from one step to another," he says, adding that there should be no milestones before maturity.
Bregier says that hydraulic pressurisation of the 'iron bird' test-bed took place at the end of December, adding that it will be used to "debug all functions at system level".
Airbus executive vice-president for programmes Tom Williams says the airframer has needed to bring the research and technology aspect, as opposed to research and development, of the aircraft to "where it needs to be".
"We're keen not to repeat the A380 experience," he says, adding that Airbus has wanted to instil "more discipline". He gives the example of certain critical components being produced in-house in order to ensure "lots more transparency and visibility".
Bregier admitted to an EADS investor gathering in Toulouse last November that the previous caution over the service-entry schedule had been driven by a desire to avoid continuing enquiries as to precisely when, 2013, the twinjet would be delivered.
"In the next months we want to be able to have the detailed configuration of the aircraft, including [system] routings and bracket locations, included in the digital mock-up of the first aircraft," he said.
"Perhaps it's a bit too demanding but, if we do that, it will be much simpler, and I prefer to take a couple more months at this stage to avoid potentially big problems."
Airbus' single, integrated A350 digital mock-up has been part of a management strategy to increase information sharing, while manufacturing has been distributed to a reduced number of first-tier suppliers, each handling larger work packages.
Over the course of 2010 Airbus secured orders for 63 A350s, bringing its order backlog for the twinjet family to 583 from 36 customers.