Airbus admits that it is experiencing difficulties with adapting its early A320 test airframe to fit the 'sharklets' wing-tips, due to enter service next year.
The manufacturer is equipping its MSN1 aircraft with the sharklets which will eventually be a key part of the A320neo airframe.
Speaking as Airbus prepared to inaugurate its new A350 wing facility at Broughton, executive vice-president for programmes Tom Williams said additonal work had been needed within the A320 wing.
"MSN1 has been heavily modified over the years," he said. "There's no data pack to tell you what it looks like."
The differences in the wing have required engineers to "hand make" components for interfaces, he added.
This work had been "tedious" rather than difficult, Williams pointed out, and while the flight-test programme has had to be re-jigged, the airframer is confident that there will be "no change" to the certification date.
Airbus had been hoping to start flying the sharklet-equipped MSN1 in October and Williams said it would certainly fly before the end of the year. Initial delivery to Air New Zealand is scheduled for 2012.