The Federal Aviation Administration is to mandate an airworthiness directive for specific models of the Boeing 787 Dreamliner, following an investigation that concluded that the shim gaps have exceeded engineering allowances. It affects 17 US-registered 787s, rather than the full US inventory, depending on their date of manufacture.

This directive would require repetitive ultrasonic inspections of splice plates, front and rear spar terminal fittings, lower cords, and jack pads for any found cracks, and detailed inspections on splice plates for any cracks as per the Federal Register airworthiness directive project identifier AD-2025-01361-T.

Investigation for Manufacturing Errors On The Boeing 787

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These findings come after the FAA received a report on Boeing that was investigated for errors in manufacturing related to excessive preload forces into the lower SOB splice plates. This is common to the lower outboard wing skins, which indicate that the shim gaps could have exceeded engineering allowances.

When operating, the high pull-up forces on these components resulted in fatigue cracks at the fastener holes. Following a structural assessment, it was found that the existing inspection program for affected aircraft was not adequate to detect the cracking in structural elements. This provided a poor limit load capacity. If this condition were not addressed, it would result in fatigue cracks that would go undetected and would result in a weaker primary wing structure.

Failing to address this issue could result in the loss of the Boeing 787’s ability to operate and land safely. The FAA issued the directive after determining that this unsafe condition was likely to exist or develop on other Boeing 787s. The fact that the AD is based on specific aircraft in the 787 family alludes to it being focused on a specific date of manufacture.

Total Cost For US Operators Exceeds $400,000

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For the 17 aircraft affected under the US register, the FAA estimated the total cost of compliance will amount to a total of $413,270 for US operators, or $24,310 per aircraft. There would be minimal costs for parts; however, up to 286 work hours per inspection cycle. Further details below:

While these costs are an estimate, some or all of the costs may be covered under the warranty for the airplane, reducing the financial burden on operators. The FAA has also confirmed that they have received no definitive data on which the estimates for the on-condition repairs were specified.

The FAA has requested comments on this directive no later than April 27, 2026, and relates to the 787-8, 787-9, and 787-10 certified in any category within a specific timeframe of manufacture. The AD also noted that the mandate would not have a significant overall economic impact due to the small number of aircraft affected.

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FAA To Require Inspections Of Boeing 787 Forward-Pressure Bulkheads

The FAA is proposing to issue an airworthiness directive on the 787 family of jets.

What Is A Shim Gap?

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An aircraft’s shim gap is a small unintentional space that sits between structural components or mating parts. These often occur during assembly and are filled with shims, a thin, precise piece of metal or liquid to ensure structural integrity. This limits vibration on the aircraft and ensures proper load distribution.

The purpose is to prevent stress points from fatigue on the aircraft, and any misalignment may compromise the airframe or components in the aircraft’s performance. Similar to wing-to-rib joints, these shim gaps are in fuselage sections and mounting areas where the materials are put under immense pressure, resulting in higher required tolerances.

Without proper shimming in these unintentional spaces, accelerated structural fatigue or failure can occur. The gaps themselves are commonly measured using a Gapman device. It is common on modern aircraft to have thousands of custom shims that then fill the gaps between unintentional structural components.