Aerospace Part Numbering: Forum Insights on Hierarchical, Random, and Hybrid Approaches

Part numbering conventions in aerospace engineering present a deceptively complex challenge. While it might appear to be a straightforward administrative task, the reality involves navigating multiple competing priorities, legacy system constraints, and regulatory requirements that make it far from simple. To better understand how different organizations approach this challenge, we initiated a discussion on the Eng-Tips engineering forum [1], engaging with experienced aerospace professionals to gather real-world insights. The resulting conversation revealed the intricate trade-offs and diverse philosophies that organizations must consider when designing their part identification systems.

Note: This article synthesizes insights from a forum discussion among aerospace professionals. While we have strived to accurately represent the perspectives shared, the analysis and thematic groupings represent our interpretation of the conversation rather than explicit positions stated by individual contributors.

The way an organization numbers its parts has significant implications for everything from design efficiency and manufacturing coordination to long-term maintenance and regulatory compliance. This article explores the key insights from that discussion, examining the practical challenges of the aerospace industry and the various approaches engineers use to identify and track the countless components that make up modern aircraft systems.

The Aerospace Difference: Why Part Numbering Matters More

Unlike many other industries, aerospace operates in an environment of exceptionally high stakes. The mission-critical nature of every component, combined with product lifecycles that can span several decades, creates a unique set of challenges. Add to that the stringent traceability requirements from regulatory bodies like the FAA and EASA, and the complexity of integrating components from a global multi-supplier network, and it becomes clear why part numbering is not just an IT problem, but a fundamental engineering and safety issue. The need to track a part's history, from its initial design and manufacture through its entire service life, is essential.

The Great Divide: Philosophy and Practice

The forum discussion suggested a fundamental philosophical divide in how to approach part numbering. There is no single, universally accepted "best practice," but rather a spectrum of approaches, each with its own set of trade-offs. The two main camps can be broadly categorized as "Team Hierarchical" and "Team Random," with hybrid approaches also emerging.

Team Hierarchical: The Case for Logic and Organization

Several forum participants appeared to favor hierarchical naming schemes that embed meaningful information directly into the part number itself. The discussion revealed various approaches to this philosophy, including Work Breakdown Structure (WBS) integration, ATA chapter system alignment, and embedding mission/project context directly in the filename structure. One contributor shared their preference for WBS-based schemes, noting that "the part number gives some indication of function and location" [1].

The forum discussion included specific examples of hierarchical systems in practice. One participant described using formats like "MISSION_PARTNO_NAME_REV.SUBREV" with examples such as "PROJ-A_4301-01-00_ReactionWheels_01" where 8-digit part numbers create a hierarchy with 4000s representing platform components and 3200s representing power systems [1].

However, forum contributors also acknowledged the risks of this approach. The central tension emerged in the discussion around whether the benefits of logical structure outweigh the potential for human error. As one participant questioned, "How do you weigh the benefits of logical structure for findability against the risk of human error from similar numbers?" [1].

Team Random: The Case for Error-Proofing and Simplicity

The forum discussion included contributors who strongly supported what we have characterized as the "Team Random" or "non-intelligent" approach. These contributors prioritized error prevention above all else, arguing for simple, meaningless, and often randomly generated numbers. One forum participant made a compelling case against alphanumeric characters, arguing that they "only introduce additional sources for errors" and that a purely numeric system is "the most universal language." Their specific advice was to avoid sequential numbering altogether, ensuring that a "fat-fingered character should produce a wildly incorrect part" [1].

This philosophy was expressed even more forcefully by another forum contributor, who offered a particularly blunt assessment:

"Smart part numbers are among the dumbest, most costly ideas pushed by MBAs in recent decades." [1]

The forum discussion highlighted how this approach prioritizes significant reduction in human error. However, participants also acknowledged that it comes at the cost of losing logical organization and findability, placing much heavier reliance on the search and metadata capabilities of PLM or PDM systems.

Team Hybrid: The Pragmatic Middle Ground

The forum discussion also revealed practitioners who have found middle-ground approaches between the two extremes. One contributor mentioned using "strictly 8-digit numbering with barcodes on the physical product," noting that "anything that removes the human element from part identification is a good thing" [1]. This represents a hybrid philosophy that maintains some structure while incorporating error-prevention measures.

A particularly compelling example emerged from a contributor whose small company has successfully used the same hybrid system for over 100 years, managing 50,000+ parts with a format like "X-025.00.01" where each segment indicates sector, type, system configuration, and sequential part identity. As they noted, "the system has worked for over a 100 years and still going strong" with just "8 rules of the numbering convention to follow" [1]. This demonstrates how well-designed hybrid approaches can achieve remarkable longevity.

The discussion suggested that many organizations in practice opt for such semi-intelligent approaches that balance the competing priorities. This typically involves using category-based prefixes to group parts into logical families, followed by sequential numbers. As outlined in industry best practices [2], this approach provides a balance between the organizational benefits of hierarchical systems and the error-prevention advantages that forum participants debated.

Real-World Case Studies: Lessons from the Forum

Our forum discussion provided a rich collection of real-world experiences that illustrate the practical challenges of part numbering in aerospace. Forum participants shared specific examples from their careers that highlight how different operational contexts drive different numbering solutions.

Helicopter Modification Shop Experience: One forum contributor detailed their experience working in a helicopter modification shop dealing with Supplemental Type Certificate (STC) packages. They explained how managing drawing revisions with approvals in multiple countries created complexity, leading to systems where "parts unique to each package" were used to control configurations [1].

GA OEM Search Challenges: The same contributor contrasted this with their experience at a General Aviation (GA) Original Equipment Manufacturer, where poor system searchability often meant "walking around the assembly hall" to physically locate and identify components. They shared a specific example of duct bulk head fittings where "1" duct fitting had a 71 ATA based PN while the 2" had 23 ATA based PN," illustrating how inconsistent numbering schemes complicate parts identification [1].

These forum anecdotes led to a critical observation that emerged from the discussion:

"Do you find that part numbers end up carrying more information than they should because the systems can't search descriptions or metadata effectively?" [1]

This observation gets to the heart of the issue: many part numbering conventions are workarounds for the limitations of underlying data management systems.

The COTS Conundrum: Integrating Commercial Off-the-Shelf Parts

The forum discussion revealed that integrating Commercial Off-the-Shelf (COTS) parts adds significant complexity to part numbering decisions. As one contributor bluntly stated, a "whole (dull) textbook could be written on this" topic [1]. The forum participants identified the core challenge as managing traceability and approval of parts not designed and manufactured in-house, with careful consideration needed for Technical Standard Order (TSO) authorizations and other regulatory requirements.

Forum contributors debated whether to use manufacturer part numbers or assign internal ones. The discussion revealed practical experience with both approaches. One participant shared their strategy of placing internal part numbers on COTS parts to maintain supply chain control, citing a specific example of an agricultural aircraft manufacturer buying plastic chopping boards at a local chain store for canopy slides. When someone used the last one in stock, "panic ensued about just which ones were they buying" because "the details of just what they were buying was lost" over time [1]. This real-world example from the forum illustrates why COTS numbering strategy matters for long-term supportability.

The forum discussion also highlighted obsolescence management as "another issue to watch for" when dealing with COTS parts [1], emphasizing how numbering decisions impact long-term maintenance and support.

It's worth noting that the complexity of COTS integration primarily applies to commercial parts that require internal tracking and approval processes. As one forum contributor observed, "standard hardware part numbers" are typically straightforward—"they are what they are" and rarely create numbering challenges [1]. The real complexity emerges with COTS parts that need internal part numbers for supply chain control, traceability, or regulatory compliance purposes.

The Historical Dimension: How Numbering Systems Evolve

One of the most insightful perspectives to emerge from our forum discussion was the recognition that part numbering systems do not exist in a vacuum—they evolve over time as companies grow, technologies change, and organizational needs shift. As one experienced forum contributor noted, there is "another slippery category of numbering... 'HISTORICAL TRANSITION'... what has been... in each company as it evolves" [1].

This historical perspective reveals a dimension of complexity often overlooked in theoretical discussions of part numbering best practices. Organizations frequently find themselves managing multiple numbering schemes simultaneously, dealing with legacy systems that cannot be easily changed, and navigating the challenges of technology transitions that fundamentally alter how parts are designed, manufactured, and documented.

Technology Transitions and Their Impact

The forum discussion highlighted how major technology shifts create unique numbering challenges. One contributor with extensive experience across multiple drawing systems observed how "hand drawings transitioned to CAD drawings that were equivalent to hand-drafting just more accurate... to an insane variety of high-end CAD/CAM/FEA/Sim/Digital-Twin... etc capable systems" [1]. Each of these transitions brought new capabilities but also new constraints and requirements for part identification.

A particularly compelling example emerged from the discussion of Lockheed's F-16 program, where the contributor noted that the drawing system was so well-structured that "I could look at a drawing number and a could closely guess what the drawing was all about... assembly or details... obviously the -# became very specific for exact configuration of 'similar-to' parts... on separate sheets" [1]. This represents an example of a hierarchical system that worked exceptionally well within its historical context, even as it might not translate directly to modern PLM environments.

Legacy System Constraints

The historical dimension also encompasses the reality that most organizations must work within the constraints of existing systems and established part libraries. As the forum discussion revealed, "standard hardware part numbers" are typically "what they are" and rarely problematic [1]. The challenges arise primarily with custom and engineered parts where organizations have more control over numbering decisions.

Company standardization processes also evolve over time, with what one contributor described as standardization becoming "the 'norm' for translation" [1]. This suggests that successful numbering systems often emerge organically through company-specific evolution rather than being imposed as complete solutions.

The Challenge of Multiple Numbering Schemes

The historical perspective reveals that many organizations end up managing multiple numbering approaches simultaneously. Different product lines, acquired companies, or technology platforms may each bring their own numbering conventions, creating a complex landscape that must be navigated carefully. The forum discussion suggested that the most successful organizations are those that can maintain flexibility while gradually harmonizing their approaches over time.

Standards Evolution and Future Considerations

The discussion also touched on how industry standards themselves are evolving. References to ASME Y14.100 for "rational drawing systems" and ASME Y14.41 Digital Product Definition Data Practices point toward a future where "everyone needs to become a 'CAD-driver' to interpret drawings" [1]. Military standards like MIL-HDBK-539 for Digital Engineering and Modeling Practices further illustrate how the regulatory landscape is adapting to new technologies.

These evolving standards create additional complexity for organizations trying to balance historical compatibility with future requirements. The forum contributor noted that "3D all-digital data that results in break out 'digital twins' has unique challenges/opportunities and rigorous accountability" [1], suggesting that the historical transition challenges are far from over.

Technology and System Limitations: The Tail Wagging the Dog

A recurring theme in the discussion was the extent to which technology and system limitations dictate part numbering strategies. The limitations of legacy Product Lifecycle Management (PLM), Enterprise Resource Planning (ERP), and other data management systems often force organizations to adopt convoluted numbering schemes as a workaround. The "search problem" is a prime example of this. When a system's search capabilities are weak, engineers are forced to embed more information into the part number itself, leading to the kind of "intelligent" numbering systems that are prone to error.

This creates a vicious cycle: the limitations of the technology drive the adoption of a complex and error-prone process, which in turn makes it more difficult to migrate to a new, more capable system. The ideal solution, as suggested by the best practices from Durolabs, is to base the part numbering system in a centralized PLM system that can act as a single source of truth and validate new part numbers to prevent duplicates [2]..

Industry Standards and References: Providing a Common Language

While there is no single standard for part numbering, there are several industry standards and references that provide a common language and framework for aerospace documentation. The most prominent of these is the ATA iSpec 2200, which provides a global standard for the content, structure, and electronic exchange of aircraft engineering and maintenance information [3]. The ATA system divides the aircraft into chapters, providing a standardized way to categorize and reference different systems. For example, the fuel system is always found in chapter 28, regardless of the aircraft manufacturer.

Technical Drawing and Documentation Standards

The forum discussion highlighted several key technical standards that influence part numbering decisions. ASME Y14.100 provides guidelines for rational drawing systems and establishes principles for engineering drawing practices that many organizations use as a foundation for their numbering approaches [1]. This standard helps ensure that part identification systems align with broader documentation practices.

Looking toward the future, ASME Y14.41 Digital Product Definition Data Practices addresses the emerging challenges of digital engineering environments. As one forum contributor noted, this standard "for-tells the future where everyone needs to become a 'CAD-driver' to interpret drawings... unless the CAD is also directed to produce conventional drawings for mortal eyes" [1]. This evolution toward digital-first documentation has significant implications for how parts are identified and tracked.

Military and Defense Standards

For organizations working in defense and military applications, MIL-HDBK-539 Digital Engineering and Modeling Practices provides specific guidance for digital engineering approaches. The forum discussion noted that "the Military is leading the way... at least for MIL" in establishing these new digital practices [1].

An important practical constraint highlighted in the forum discussion is that military applications often have physical limits on part number length. As one experienced contributor noted, there is "a physical limit to the 'digit count'... combination of numbers, letters, symbols and punctuation" that "cannot be violated" in DoD applications [1]. While the exact digit count limit wasn't recalled, this constraint has significant implications for numbering system design in defense applications.

Established Nomenclatures and Legacy Systems

In addition to formal standards, there are other established nomenclatures, such as the MS/NAS military standards and the hardware designation systems used by large manufacturers like Boeing. These standards provide a degree of consistency and interoperability within their respective domains, but they do not solve the fundamental problem of creating a universal part numbering system. The forum discussion emphasized that these various standards often coexist within a single organization, creating the need for translation and mapping between different numbering approaches.

Practical Recommendations: Finding the Right Fit

Given the diversity of opinions and practices, how can an organization determine the best approach for its own needs? The key is to conduct a thorough assessment of the company's specific context, including its size and complexity, legacy system constraints, regulatory requirements, supply chain complexity, and team capabilities. There is no one-size-fits-all solution, and what works for a large OEM may not be appropriate for a small MRO.

When implementing a new or revised part numbering system, a phased migration approach is often the most practical solution. This allows for a gradual transition and minimizes disruption to ongoing operations. Designing a hybrid system that incorporates the best elements of both the structured and random approaches can also be an effective strategy. Finally, any new system must be accompanied by thorough training and a clear adoption plan to ensure that it is used consistently and effectively.

The Flexibility Principle: Embracing "Good Enough"

Perhaps the most insightful comment in the entire forum thread offered a dose of pragmatic wisdom:

"If there was a single magic 'best practice' that worked for everything, then everyone would use it. There isn't, and that's ok. Do what works for your unique situation." [1]

This sentiment was followed by another key insight:

"In general, the more rules you try to apply to a numbering system the more likely a future case breaking the system becomes. So, favor flexibility over a rigid set of rules." [1]

This "flexibility principle" is a crucial takeaway from the discussion. The pursuit of a perfect, all-encompassing part numbering system is often a fool's errand. The most effective systems are those that are adaptable and can evolve with the needs of the organization. A system that is "good enough" and can be applied consistently is often superior to a complex and rigid system that is difficult to maintain. As one forum contributor with over a century of organizational experience observed, their numbering system "has worked for over a 100 years and still going strong" precisely because it balances structure with flexibility, noting that while "special cases occur that require case-by-case evaluation," the core system remains robust [1].

Conclusion: An Evolving Debate

Our investigative forum discussion provides a valuable snapshot of the ongoing debate surrounding part numbering conventions in the aerospace industry. It is a complex issue with no easy answers, and the diversity of opinions reflects the wide range of operational contexts and philosophical approaches within the industry. The tension between the desire for logical organization and the need for error prevention is likely to persist, but the conversation itself is a healthy sign of an industry that is constantly striving to improve its processes and ensure the highest levels of safety and reliability.

As technology continues to evolve, with advancements in AI-assisted search and blockchain for traceability, the nature of this debate may change. But for now, the key takeaway is that there is no single "best practice," only a series of trade-offs that each organization must weigh for itself. The most successful companies will be those that can find the right balance for their unique situation and create a system that is both robust and flexible enough to adapt to the challenges of the future.

Acknowledgments

This article is based on a forum discussion that we initiated on Eng-Tips in July-August 2025 as part of an investigative effort to better understand real-world part numbering practices in aerospace. Our goal was to engage directly with experienced professionals and gather authentic insights from the field. We extend our gratitude to all the contributors who generously shared their valuable insights and real-world experiences: Ng2020, TugboatEng, verymadmac, ewh, CWB1, MintJulep, WKTaylor, and Prometheus21. Their diverse perspectives and practical wisdom from various sectors of the aerospace industry—from helicopter modification shops to GA OEMs to large manufacturers—made this comprehensive analysis possible and provided the authentic, ground-level insights that no textbook could offer.

Special recognition goes to WKTaylor for providing thoughtful feedback on this article and suggesting the important addition of the "Historical Transition" perspective, which significantly enhanced the comprehensiveness of this analysis. The ongoing dialogue demonstrates the collaborative nature of professional engineering communities and their commitment to sharing knowledge for the benefit of the industry.

References

[1] Eng-Tips Forum. (2025). Part numbering conventions - what's the best practice in aerospace? [Online]. Available: https://www.eng-tips.com/threads/part-numbering-conventions-whats-the-best-practice-in-aerospace.565772/

[2] Duro Labs. (2022). Part numbering systems: 7 best practices to optimize the process. [Online]. Available: https://durolabs.co/blog/part-numbering-systems-best-practices/

[3] AviationHunt. (2023). ATA Standard Numbering System. [Online]. Available: https://www.aviationhunt.com/ata-standard-numbering-system/

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