Airbus has given further details of the issues which led the airframer to push back the assembly schedule for its A350 twinjet.
Chief operating officer Fabrice Bregier, during an EADS investor presentation last week, said the rear spar manufacturing "took longer than expected", slowing the industrial process for the wing.
He admitted that controlling the quality and ramp-up of detailed carbonfibre parts presented "major difficulties".
Missing frames, clips and brackets had led to delays in the assembly processes with Airbus's risk-sharing partners, according to Bregier's presentation.
First fuselage barrel assemblies had been performed with "appropriate tolerances", it added, but more time was necessary to freeze detailed interfaces and drawings.
Airbus is aiming to start final assembly of the first airframe, the static example of the A350-900, early next year.
Latest A350 assembly efforts have involved transferring the first rear fuselage, section 19, from the Spanish manufacturing facility in Getafe to the centre at Hamburg, the airframer said through its official social media channel.