787 programme as it moves to redesign this critical structural component.
Flight has learnt that testing revealed that the 787’s composite centre wing spars, that hold the structure of the wingbox together, buckle more easily than metal spars. The composite spars were originally designed within non-buckle tolerances, but as weight crept up subsequent design iterations saw their width reduced.
Sources inside the programme say the buckling was discovered after the wing boxes were manufactured, and as it is too late to increase the thickness of the spars on six airframes already under construction (four flight-test aircraft and two test specimens), they will be modified with stiffeners.
These have already arrived at the final assembly line at the Everett, Washington, factory and will negate the weight savings sought by reducing their width originally. At some point a redesigned wingbox will be introduced.
According to one source: “Similar design changes happened in 777. But the difference is that 787 was so far away from weight target that many weight-reduction ideas were adopted even though they were high risk due to lack of supporting test data or manufacturing experience.”
The first public indications of a wing box problem came from Boeing’s largest 787 customer, International Lease Finance. Chairman Steven Udvar-Hazy reportedly told a JP Morgan analyst last week that he does not expect the first delivery to occur until the third quarter of 2009 as a result of structural design changes that are needed to the centre wingbox, implying a six-month delay.
In response Boeing reportedly said: “While we respect Hazy and he is a valued customer, what he was sharing is his opinion.” It confirmed to Flight that it was “working with partners to address the need for design changes in some areas”.
Separately, Boeing is reorganising the lean manufacturing process designed for the 787 programme. According to sources, a system of “super mechanics”
who hold all the necessary certifications to self-check work to appropriate airworthiness standards is being abandoned in favour of a traditional quality-assurance system. The sources say over the past year of assembly the self-certification process had become an impediment to progress rather than an enabler of efficiency.
As a result, the 787 programme has begun to shift from a system of self-certificating staff to a more traditional system of quality assurance similar to Boeing’s legacy programmes.
The revised system is first being implemented for out-of-sequence travelled work and is expected to be expanded to the entire final assembly process.
Boeing sources attribute the slow pace of assembly work to what are known as “rejection tags”. Each rejection tag identifies a “non-conformance” in the design that must be checked through a quality certification process. But by using its traditional quality assurance system, Boeing is able to better control and group the number of rejection tags to reduce paperwork and solution time
Source: Flight International
