While removing and reapplying sealant to each 787 remains critical in preparing for delivery, the workmanship of its application is not the only item Boeing has identified for change inside the aircraft’s composite wings; a design change discovered in the fall of 2009 requires the removal and replacement of thousands of improperly coated fastener joints to ensure the majority-composite jetliner’s protection from lightning strikes.
The removal of the sealant will allow access to the thousands of wing fuel and hydraulic system fastener joints which were designed and installed with an improper coating, and have to be removed and replaced to meet US Federal Aviation Administration requirements for electromagnetic effects (EME) protection for lightning strikes.
Despite receiving wings from Japan’s Mitsubishi Heavy Industries (MHI) with the correct sealant application “for a while” now, Boeing says it will be required to conduct “a significant amount of resealing work that needs to be accomplished on all 787 wings” as a result of the fastener joint changes.
A fastener joint is anywhere a fastener is used to join two pieces of hardware together, and in the case of the fuel system for example, says one engineer, includes brackets to a structure or a tube clamp to a bracket.
FAA requirements for EME protection as part of Part 25 Secton 954 and 981 require all joints and fasteners to be installed in a way that prevents any sparking within the fuel that could lead to a catastrophic ignition.
Because the 787′s structure is majority composite, which does not conduct electricity like traditional metals, Boeing has had to meticulously design the metallic parts in the aircraft, including the incorporation of an elaborate current return network, to prevent sparks and arcing, as well as withstand lightning strikes.
Those directly familiar with the issue say the test fleet of six 787 has the same configuration as those jet currently requiring rework, but did not need the fastener joint modifications prior to flying, as Boeing employs a fuel with anti-static additives for test flights preventing any possible spark.
In fact, ZA001, Boeing’s lead 787 test aircraft suffered a lightning strike in May 2010, with no trace of damage to the aircraft beyond instrumentation inside the right wing where the bolt was believe to have hit.
The issue was first discovered in fall 2009, when barely a handful of production 787s had entered final assembly. Boeing has continued deliveries to final assembly, pausing several times in 2010 to allow shipsets to arrive at a higher level of assembly completion, but opted to push the wing fastener joint rework to change incorporation after assembly, though wings with this design issue continue to arrive in Everett from Japan.
The Seattle Times reported Tuesday that the process of removing and reapplying the sealant inside the wings of each 787 was “taking weeks per airplane” and was likely to slow the planned pace for 12 to 20 deliveries in 2011.