Boeing says this is the result of a need to reinforce an area within the side-of-body section of the aircraft.

"Consideration was given to a temporary solution that would allow us to fly as scheduled, but we ultimately concluded that the right thing was to develop, design, test and incorporate a permanent modification to the localised area requiring reinforcement," said Scott Carson, president and CEO of Boeing Commercial Airplanes.

"Structural modifications like these are not uncommon in the development of new airplanes, and this is not an issue related to our choice of materials or the assembly and installation work of our team," he added.

The new schedule for first flight and first delivery of the aircraft will be announced in a few weeks time.

Structural reinforcement

In a Boeing webcast on 23 June company officials discussed this development further.

The problem was identified during routine testing involving bending of the aircraft wings where areas exhibiting higher than expected levels of stress were found.

According to Scott Fancher, vice president and general manager of the 787 Dreamliner programme, the issue involves 1-2 square inch areas in multiple locations (around 32 locations in total) along the upper portion of the wing to body join on both sides of the aircraft. These areas incorporate several materials – titanium, aluminium and composites.

The company says the localised reinforcement required is 'quite manageable', involving a small number of parts. These parts could be titanium or aluminium depending on the modification design chosen. Boeing will work with Mitsubishi (the wing supplier) and Fuji Heavy Industries (the supplier of the body part) to develop a modification, which will be applied to all aircraft in production.

Boeing stresses that there will be no impact on the weight or performance of the aircraft.