Boeing 737–9 Incident: A Tale of Neglected Procedures and Quality Control

In an eye-opening disclosure from an anonymous Boeing employee, the recent incident involving a Boeing 737–9 registered as N704AL, where a mid-exit door plug blew off has been attributed to a series of overlooked safety procedures and quality control failures within Boeing. This account, though unverified, provides a detailed insight into the internal operational challenges at Boeing, particularly in its 737 production line. This article is based on the assumption that the anonymous Boeing employee is truthful and factual, the data and facts presented here are not mine.

The incident involving the detachment of the left-hand (LH) mid-exit door plug on the Boeing 737–9, registered as N704AL, is attributable to a series of systemic failures and oversights in the production and quality assurance processes. The underlying cause was the absence of four critical bolts, which are integral to securing the mid-exit door plug in place against the pressures experienced during flight. These bolts were missing from the outset, as Boeing’s delivery records for this aircraft confirm their non-installation.

Source: https://www.flightaware.com/photos/view/4683316-f07195b02bcf798755b68c1e636ffe3e03da34d1/aircrafttype/7379

To elaborate, the mid-exit doors of a Boeing 737–9, including both standard and plug types, are initially installed by Spirit AeroSystems. These doors are intended to be delivered in their final configuration. Upon arrival at Boeing’s Renton factory, a specific protocol is in place for the doors team to verify and ensure that the installation and rigging of these doors align with the designated engineering drawings. This verification process is designed to act as a redundant check within a robust production system, serving as an additional layer of quality assurance. However, the 737 production line has been plagued by significant systemic issues. Over the past year, a concerning total of 392 nonconformities have been recorded in relation to the mid-fuselage door installations on the 737, including both actual doors and plugs like the one in question. This rate of defects is alarmingly high and indicative of deep-rooted quality control problems. In a well-functioning quality system, such anomalies would have triggered a halt in production and a thorough investigation, potentially leading back to the supplier. Unfortunately, this did not occur.

Source: https://www.seattletimes.com/business/boeing-aerospace/boeing-not-spirit-mis-installed-piece-that-blew-off-alaska-max-9-jet/

In the specific case of the incident aircraft, the verification check was completed on August 31, 2023. This check did reveal discrepancies, but only in relation to the right-hand (RH) side door, not the LH door that ultimately failed. Given the high volume of defects being processed, it was perhaps inevitable that some issues would be overlooked, as happened with this aircraft.

Adding complexity to the situation, on September 1, 2023, a different team identified issues with the installation and damage to rivets on the LH mid-exit door of the same aircraft. Boeing employs two primary record-keeping systems for production: CMES (Computerized Manufacturing Engineering System), the authoritative database for build records, and SAT (Systematic Assembly Tracker), a less formal tool used for internal coordination and management oversight. Despite its non-authoritative nature, SAT is heavily utilized for day-to-day management and problem-solving discussions.

Source: https://aviationweek.com/aerospace/manufacturing-supply-chain/boeing-leans-quality-system-end-787-crisis

For this particular aircraft, the rivet issue was recorded in both CMES and SAT. The SAT record, in particular, was used to coordinate a response, though it also served a managerial purpose. Spirit AeroSystems, responsible for many of the assembly defects on the 737, has teams on-site at Renton to address warranty-related issues. The defective rivets fell into this category and were thus assigned to Spirit for rectification. However, a subsequent inspection by a Boeing Quality Assurance (QA) team revealed that Spirit had merely painted over the defective rivets instead of properly addressing the issue, a significant process failure.

This discovery led to further investigations, during which it was revealed that a damaged pressure seal also needed replacement. This seal is located between the door plug and the fuselage, necessitating access to the seal by opening or removing the door plug. Such an operation would require the removal of the four critical retaining bolts. A key procedural lapse occurred here: a formal ‘Removal’ record, which is mandatory for any such operation and necessitates QA verification, was not created in CMES. This oversight meant that there was no official acknowledgment or inspection of the door opening process and the subsequent replacement of the bolts.

Source: https://www.seattletimes.com/business/boeing-aerospace/boeing-not-spirit-mis-installed-piece-that-blew-off-alaska-max-9-jet/

This entire chain of events was documented in the SAT system. However, the official records in CMES, which addressed the damaged rivets and pressure seal, did not include any mention of the door opening or bolt removal procedures. As a result, when Spirit completed the necessary repairs to the satisfaction of Boeing QA, the related CMES records were closed on September 19, 2023, without any reference to the retention bolts.

The absence of these bolts likely resulted from their being misplaced or discarded, given the lack of a formal tracking or record number in the system.

This incident is reflective of broader cultural and systemic issues within the production and quality assurance processes at Boeing, particularly within the 737 production line. The forthcoming National Transportation Safety Board (NTSB) report is expected to articulate these issues in more detail.