FAA Proposes 787 Inspections for Manufacturing Shim Gap Flaws

The U.S. Federal Aviation Administration (FAA) has released a Notice of Proposed Rulemaking (NPRM) for an Airworthiness Directive (AD) that would mandate repetitive inspections on certain Boeing 787 aircraft. The proposed rule targets potential fatigue cracking resulting from oversized 'shim gaps'—a known manufacturing tolerance issue. According to the FAA's docket, the directive would directly affect 17 US-registered Boeing 787s.

The action addresses what the FAA describes as an unsafe condition related to oversized gaps at the lower Side of Body (SOB) splice plates. If not corrected, this condition could lead to fatigue cracking, reduced structural integrity, and potential loss of the airplane. The proposed AD is the latest development in a long-running saga concerning Boeing's manufacturing quality control, specifically related to fuselage section joins on its composite-body Dreamliner.

Directive Details and Requirements

The proposed rule, detailed in Docket No. FAA-2026-2295, stems from Boeing's discovery that certain structural joints were assembled with gaps exceeding engineering tolerances. To mitigate the risk of premature fatigue, the FAA's proposal would require operators of the affected aircraft to perform repetitive inspections. These inspections include both Ultrasonic Testing (UT), a non-destructive method to detect subsurface flaws, and a Detailed Inspection (DET), which is an intensive visual check.

The inspections specifically target the SOB splice plates, spar terminal fittings, chords, and jack pads for any signs of fatigue cracking. The proposed compliance timeline and inspection intervals would be finalized after a public comment period. This move formalizes actions that Boeing had previously recommended to operators. According to the FAA, Boeing issued an Alert Requirements Bulletin, B787-81205-SB570048 RB, on August 11, 2025, to address the issue.

Boeing's Position and Historical Context

Boeing has publicly supported the FAA's proposed mandate, stating that the root cause of the shim gap issue has been identified and corrected in current production lines. The manufacturer has also emphasized that the global 787 fleet can continue to operate safely. In a statement defending the aircraft's structural integrity, Boeing Functional Chief Engineer Steve Chisholm noted that the company conducted full-scale 787 fatigue testing equivalent to 165,000 simulated flights, which resulted in zero findings of fatigue in the composite structure.

This perspective frames the issue as a localized manufacturing non-conformance rather than a systemic design flaw. However, the problem of shim gaps is not new for the 787 program. Between 2020 and 2022, Boeing was forced to halt 787 deliveries for more than a year to address this and other quality control issues. The rework on dozens of undelivered jets created a significant backlog and financial strain for the company, placing its manufacturing processes under intense scrutiny from both regulators and customers.

Technical Analysis

The FAA's decision to issue a formal Airworthiness Directive represents a significant escalation in regulatory oversight, directly influenced by recent events. While the shim gap issue predates it, the current regulatory environment has been reshaped by the January 2024 mid-air blowout of a door plug on an Alaska Airlines Boeing 737 MAX 9. That incident led the FAA to ground the MAX 9 fleet, cap Boeing's production rates, and implement a far more stringent, hands-on approach to quality assurance at the manufacturer's facilities.

This proposed 787 AD can be seen as a direct consequence of that heightened scrutiny. While Boeing previously addressed the shim gap issue with a service bulletin, the FAA is now mandating compliance through a legally enforceable AD. This development indicates that the regulator is no longer willing to rely solely on manufacturer recommendations for issues tied to production quality. It follows a pattern of the FAA taking a more prescriptive role to ensure that manufacturing variations, even those not deemed to pose an immediate threat to flight safety, are formally tracked and corrected across the in-service fleet.

For airlines operating the 17 affected aircraft, the directive will necessitate scheduling operational downtime for the required inspections, incurring costs for labor and any potential repairs if cracks are discovered. For Boeing, it represents continued reputational damage related to its production systems, even as the company works to overhaul its quality management.

What Comes Next

The proposed rule is currently in a public comment period, which, according to the FAA docket, is scheduled to end on April 27, 2026. During this 45-day window, stakeholders, including airlines and maintenance providers, can submit feedback to the FAA. Following the comment period, the agency will review the input before publishing a final rule. The issuance of the final Airworthiness Directive is expected in mid-to-late 2026, after which operators of the affected aircraft will be required to comply with its inspection mandates.

Why This Matters

This proposed directive is significant because it demonstrates the FAA's new, less tolerant posture toward manufacturing non-conformities at Boeing. While the immediate impact is limited to a small number of aircraft, it signals that any deviation from design specifications, particularly those with long-term structural implications, will now likely trigger formal regulatory action. For the wider aviation industry, it reinforces the trend of intensified oversight on production quality, a direct legacy of the 737 MAX crises.