Lightning protection prompts major 787 fastener joint re-work

Washington DC
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As Boeing removes and reapplies sealant to the wings of each 787 in preparation for delivery, it will also have to remove and replace thousands of improperly coated fastener joints to ensure the majority-composite aircraft's protection from lightening strikes.

This requirement follows a design change discovered in the second half of 2009.

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 FAA 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 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 Section 954 and 981, obligate 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 mainly 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 to withstand lightning strikes.

Those directly familiar with the issue say the test fleet of six 787s has the same configuration as those jets currently requiring re-work, but did not need the fastener joint modifications prior to flying. This is because Boeing employs a fuel with anti-static additives for test flights, preventing any possible spark.

In fact, ZA001, Boeing's lead 787 test aircraft, was struck by lightning in May 2010, with no trace of damage to the aircraft beyond instrumentation inside the right wing where the bolt was believed to have been hit.

The issue was first discovered in autumn 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 delay the wing fastener joint re-work until after assembly. However, wings with this design issue continue to arrive in Everett from Japan.

Today, more than 35 787s already delivered to Everett will require this re-work, including test aircraft ZA004, ZA005 and ZA006, which will likely be refurbished and delivered as business jets.

The airframer says it has "worked with MHI to develop a detailed plan to accomplish this work to ensure that airplanes already in production are brought up to standard and that future wings are delivered to Everett without the need for re-work".

The Seattle Times reported on 26 April 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.

The company is conducting 787 re-work operations at Boeing ATS "Factory South", the 40-24 building inside the main Everett factory, as well at its Global Service & Support site in San Antonio, Texas.

Boeing says "the overall resealing work is well understood and already a part of the programme's plan".

It adds that "this work was identified and planned for prior to the announcement of the programme schedule" in January, which slid first delivery to Japan's All Nippon Airways from early 2011 to the third quarter, following a fire aboard test aircraft ZA002 in November.