Other Aircraft Parts and Auxiliary Equipment Manufacturing (U.S.) — NAICS 336413

An investor's primer. Figures are U.S. federal statistics unless noted; company financials and market values are for the investable-universe and how-to-invest sections only.

1. Overview

This industry makes the components that go onto an aircraft but are not the airframe shell, the engine, or a missile: landing gear, wheels and brakes, propellers, flight-control surfaces, actuators, pumps and valves, fasteners, structural castings and forgings, interiors, lighting, sensors, and auxiliary gear such as external fuel tanks and in-flight refueling equipment [1]. It is the deep, fragmented supplier base beneath Boeing, Airbus, and the defense primes.

Why an investor cares: aircraft-parts making is one of the highest-quality manufacturing businesses in the economy. Certified parts are protected by regulation and often sole-sourced, the buyers are locked in for the 20-to-30-year life of an aircraft, and — critically — every part sold new generates decades of far more profitable replacement (aftermarket) sales. TransDigm notes that a typical aircraft platform may be produced for 20–30 years, while its components can have a total product life cycle exceeding 50 years [2]. Aerospace and defense is the only U.S. manufacturing sector that runs a consistent trade surplus, roughly $109 billion in 2025, larger than any other manufacturing category [3].

Ways in: the sector is unusually accessible to public-market investors (a dozen-plus listed suppliers plus sector ETFs) and equally central to private investors — private equity has been aggressively buying these businesses (Barnes Group and Triumph Group both went private in 2025), and the industry runs on privately held and foreign-owned suppliers and captive divisions of larger firms.

2. What it is, and how it's structured

Scope. NAICS (North American Industry Classification System) 336413 covers establishments that make aircraft parts and auxiliary equipment other than engines and fluid-power subassemblies, plus firms that develop and prototype such parts [1][4]. Typical products: landing gear, wheels and brakes, propellers and rotors, control-surface assemblies, airframe sub-assemblies, actuation and motion-control systems, and auxiliary items like armament racks and crop-dusting apparatus [1].

What it explicitly excludes (and where those activities are counted instead):

• Aircraft engines and engine parts → NAICS 336412 [1].
• Complete aircraft and airframe manufacturing → NAICS 336411.
• Aircraft fluid-power (hydraulic/pneumatic) subassemblies → NAICS 332912 [1].
• Guided missiles, space vehicles, and their propulsion and parts → NAICS 336414 / 336415 / 336419 [1].
• Maintenance, repair, and overhaul (MRO) of in-service aircraft as a service (rather than parts manufacturing) → NAICS 488190.

Operative unit. The Census tracks establishments, not consolidated companies. A diversified supplier may have an airframe-components plant classified in 336413, an actuator plant in fluid-power manufacturing, and an avionics plant in electronics. Company revenue cannot be assigned wholesale to this industry, and segment sales cannot simply be summed into a defensible NAICS market size.

Ownership mix. This is a genuine mid-scale manufacturing industry — not government-run, and not a cottage trade of tiny operators. The Census counts 860 firms and 966 establishments [5][6], averaging about 108 employees per plant [6]. Ownership spans (a) listed pure-plays (TransDigm, HEICO, Loar); (b) diversified public industrials for whom aircraft parts are one segment (Howmet, Curtiss-Wright, Woodward, Moog, RBC Bearings, Parker Hannifin, Eaton, Honeywell, RTX); (c) private-equity-owned suppliers (Barnes Aerospace, Triumph); (d) foreign-owned U.S. operations (Safran); and (e) captive divisions of the primes (Collins Aerospace inside RTX; parts made in-house by Boeing, GE Aerospace, and Precision Castparts inside Berkshire Hathaway).

3. How big it is

Federal ground-truth figures for NAICS 336413:

BLS seasonally adjusted payroll employment in 336413 was approximately 105,000 in June 2025, consistent with the Census figures above [8].

Concentration is moderate at the broad NAICS level. The four largest firms took 44.9% of revenue, the top 8 took 54.9%, the top 20 took 67.8%, and the top 50 took 81.3% [5]. (The Herfindahl-Hirschman Index is suppressed in current federal data [5]; a Department of Defense study reproduced a historical 2012 four-firm concentration ratio of 47% and an HHI of 762 for 336413, implying modest concentration at that time [9].) That profile — a handful of large players plus a long tail of ~800 smaller specialists — is exactly the fragmentation the acquisitive roll-ups exploit (Section 8). However, this broad-level concentration obscures much higher concentration in individual approved components, where the winning supplier often holds a near-monopoly on a specific part number.

Undercount caveat — this line understates the true "aircraft components" economy. Two structural reasons: (1) carve-outs. Engines (336412), fluid-power subassemblies (332912), and missile/space parts (336419) are large, adjacent activities counted under other codes. (2) Vertical integration. A great deal of parts-making happens captively inside firms whose establishments are classified by their dominant product — Collins Aerospace's output rolls up under RTX, engine-hot-section castings under Precision Castparts and GE Aerospace, and, since Boeing reabsorbed Spirit AeroSystems in December 2025, more fuselage and structures work sits inside an airframe (336411) company [10]. The $33.9 billion here is the merchant parts industry — real and large, but a floor, not a ceiling, on U.S. aircraft-component activity.

4. The investable universe

Unusually for a narrow NAICS code, there is a rich public menu. Scale figures below are recent revenue and, where relevant, equity market value (mid-2026); these numbers belong to the investing sections, not the industry statistics above.

Listed pure-plays and parts-heavy companies

Diversified primes with major parts content (parts are one slice of a much bigger company): RTX (Collins Aerospace — landing gear, wheels and brakes, actuation, interiors), GE Aerospace, Honeywell Aerospace, Parker Hannifin, Eaton.

Major private / other owners. Precision Castparts — structural castings, forgings, fasteners — is owned by Berkshire Hathaway [23]. Safran (France) makes landing gear, nacelles, and wheels and brakes from U.S. plants. Triumph Group (engineered systems and proprietary components) was taken private by Warburg Pincus and Berkshire Partners for ~$3 billion, closing July 24, 2025 [24]. Barnes Group (Barnes Aerospace) was taken private by Apollo Global Management for ~$3.6 billion, closing January 2025 [25]. Beneath these sit hundreds of smaller PE- and family-owned machine shops and specialists — the long tail in the federal count.

5. How the money works

Owners earn on two distinct streams with very different economics:

• OEM (original equipment) sales — parts shipped to Boeing, Airbus, and the primes for new-build aircraft. The key gauge is content per aircraft (the dollar value of a supplier's "ship-set" on a given model). OEM work is lower-margin, capital- and working-capital-intensive, and swings with build rates.
• Aftermarket sales — spare parts and repairs consumed over the fleet's life. This is the profit engine. Aftermarket operating margins in aerospace typically run roughly 2.5-to-4 times new-equipment margins [26]. It is the classic "razor-and-blades" model: win the platform at thin OEM margins, then harvest decades of high-margin replacement demand tied to flight hours and the installed base [26].

The margin dispersion is extreme. TransDigm generated fiscal 2025 sales of $8.83 billion and a GAAP operating margin of 47.2%; it estimated that approximately 90% of sales came from proprietary products and 55% from the aftermarket [2]. Woodward's Aerospace segment generated fiscal 2025 sales of $2.31 billion and a segment earnings margin of 21.9% [16]. Hexcel reported 2025 consolidated sales of $1.89 billion and operating income of $171.6 million, an operating margin of approximately 9.1% [18]. None is a pure 336413 result, but together they demonstrate why applying one "industry margin" is misleading.

The moat comes from certification and sole-sourcing. Once a part is designed into a certified aircraft, a competitor generally cannot just build a cheaper copy — replacement parts must themselves be FAA-approved (Section 7), and much of the catalog is proprietary to a single supplier. Hexcel notes that some aerospace-qualified inputs have only one or two approved sources and that material qualification costs can make developing alternatives uneconomic [18]. That is why proprietary, aftermarket-weighted businesses (TransDigm, HEICO's flight-support group, Loar) command premium valuations: their revenue is recurring, price-inelastic (a grounded jet is far costlier than the part), and recession-resistant because airlines must maintain aircraft regardless of the economy [26].

Production model. Suppliers bid during design and development, build tooling and process capability, qualify materials and parts, and enter long-term supply arrangements. Production is usually make-to-order against customer schedules, but long raw-material lead times and uncertain OEM forecasts force suppliers to carry inventory and capacity ahead of revenue [18]. OEM work tends to carry weak early-program economics because suppliers incur tooling, hiring, training, engineering changes, scrap, and low-rate production costs before reaching efficient volume. Rate increases can initially reduce rather than improve margins if labor and suppliers cannot keep pace.

Metrics investors watch: book-to-bill (orders ÷ shipments; above 1.0 means backlog is growing), backlog (contracted future revenue), aftermarket mix (higher = more resilient, higher-margin), organic growth vs. acquisition-driven growth, and incremental margins. HEICO, for instance, reported 14% organic growth and a 22.7% operating margin in fiscal 2025, with its aftermarket-heavy Flight Support Group up 18% [14].

6. What drives demand

• Commercial build rates. The single biggest OEM driver. Boeing's 737 recovered from below 38 jets a month in early 2025 to 42 by year-end, with a planned climb to 47 in 2026 (subject to FAA concurrence); Airbus's A320neo family ran around 50-plus a month, peaking near 67 in a single month [27]. Each incremental aircraft pulls a full ship-set of parts.
• Air traffic and the installed base. Aftermarket demand tracks flight hours and fleet size. The global commercial fleet is projected to grow from roughly 29,000 aircraft in 2025 toward 38,000+ by 2035 [28]. The FAA forecasts the active U.S. commercial fleet to expand from 6,949 aircraft in 2025 to 10,677 in 2046, an average annual rate of 2.1% [29]. U.S. carrier revenue passenger miles are forecast to grow at an average annual rate of 2.6% from 2025 through 2046 [29].
• Fleet aging and deferred retirements. A record order backlog above 17,000 aircraft and slow deliveries have kept older jets flying longer, which raises replacement-part and MRO consumption [30]. The commercial MRO market alone is roughly $100 billion a year [28]. Older aircraft can be attractive aftermarket assets because they require more maintenance, but only until retirement overwhelms per-aircraft usage.
• Defense and rotorcraft budgets. Military platforms, helicopters, and business jets add non-commercial demand that is less tied to the airline cycle. Defense demand is driven by appropriations, procurement quantities, readiness and sustainment spending, foreign military sales, and geopolitics. Ducommun's 2025 mix illustrates this diversification: military and space represented 58.2% of revenue and commercial aerospace 37.4% [20].
• Lightweighting. Newer airframes and rotorcraft use more carbon fiber, honeycomb, advanced adhesives, and integrated composite structures. This is a secular content driver, though automation, digital-thread engineering, and additive manufacturing can reduce part count and labor. New manufacturing methods still require process qualification and approval on each application.

7. Regulation

Airworthiness regulation is the industry's central fact of life — a barrier to entry and the source of pricing power.

• FAA production approval (14 CFR Part 21). No replacement or modification part may be sold for installation on a certificated aircraft unless it is produced under an approval [31] — most commonly a PMA (Parts Manufacturer Approval), a combined design-and-production approval [32], or a TSOA (Technical Standard Order Authorization) for parts meeting an FAA minimum-performance standard. This is the legal seam that lets independents such as HEICO sell approved alternatives to the original maker's parts.
• Type certification. Parts designed into a new aircraft are certified as part of the aircraft's overall type certificate; overseas, EASA (the European Union Aviation Safety Agency) plays the equivalent role.
• Quality systems. Suppliers must hold AS9100 aerospace quality certification to sell into the supply chain.
• Export controls. Defense-related parts fall under ITAR (International Traffic in Arms Regulations); dual-use items fall under the EAR (Export Administration Regulations) [33]. Military aircraft components can fall under ITAR, while civil, dual-use, and transferred military items may be controlled under EAR, including aerospace "600-series" classifications. Classification, licensing, end-use restrictions, and changing sanctions can delay sales or make a market inaccessible. Both constrain who suppliers can sell to and require licensing.
• Ongoing airworthiness. The FAA issues Airworthiness Directives mandating inspections or part replacements, and polices suspected unapproved (counterfeit) parts — a live compliance and liability exposure.

8. Competitive dynamics and consolidation

Headline concentration is only moderate (top-4 at 44.9% [5]), but that understates reality: within a specific part number on a specific platform, the winning supplier often holds a near-monopoly. Competition happens at the design-in stage; after that, incumbency and certification lock share in.

The defining strategic story is roll-up consolidation of proprietary, aftermarket-rich niches. TransDigm pioneered it — buying small firms that own sole-source intellectual property and extracting pricing power (it announced multi-billion-dollar deals including Raptor Scientific and SEI Industries in the current cycle) [13]. HEICO runs a complementary model, positioning its PMA parts as an explicit cost-saving alternative to the original makers [14], and Loar is executing the same playbook at smaller scale [22].

Two other forces are reshaping the map: private equity taking suppliers private (Apollo/Barnes, Warburg Pincus + Berkshire Partners/Triumph in 2025) [24][25]; and vertical integration by the primes — most visibly Boeing reabsorbing fuselage-maker Spirit AeroSystems on December 8, 2025, with Spirit's Airbus-supplying sites carved out to Airbus [10]. The primes are simultaneously the industry's biggest customers and, through captive divisions, its largest competitors.

Supply-chain inputs. The Aerospace Industries Association's supply-chain survey identifies titanium, semiconductors, specialty alloys, aluminum, composites, and copper among members' critical-material concerns and continues to flag skilled-labor recruitment and retention [34]. Reshoring and dual-sourcing are supportive themes but collide with economics: OEMs want resilience, while the cost of certifying a second source can be prohibitive for low-volume parts.

9. Risks

• Boeing / single-platform concentration. The 737 MAX and 787 quality and production troubles rippled straight through the supplier base; a supplier levered to one OEM or one program carries that OEM's execution risk. Hexcel reported that Airbus and Boeing and their subcontractors represented approximately 77% of its 2025 commercial-aerospace sales [18].
• Deep cyclicality on the OEM side. Air travel is economically sensitive; the 2020 pandemic cut global traffic by more than half and gutted new-build demand. Aftermarket cushions the blow but does not eliminate it.
• Supply-chain and input costs. Titanium (historically sourced partly from Russia), specialty castings and forgings, and — persistently — skilled machinists are chronic bottlenecks; IATA estimated supply-chain disruptions cost airlines over $11 billion in 2025 [30]. Long-term agreements improve visibility but can trap a supplier between fixed or lagging prices and rising labor, material, freight, or tariff costs.
• Certification and quality exposure. A defect can trigger inspections, rework, delivery stoppages, warranty claims, grounding exposure, and product-liability litigation, while loss of an approval can eliminate a revenue stream. Export-control (ITAR/EAR) missteps carry heavy penalties.
• Tariffs and trade. A globally integrated supply chain is exposed to tariff and trade-policy shifts.
• Financial leverage. The roll-up and PE-owned models often run high debt; rising rates or a demand shock pressure the most leveraged names first. TransDigm's fiscal 2025 interest expense was $1.57 billion, illustrating that even exceptional operating economics come with substantial financial risk in acquisition-led models [2].
• Labor. Machinists, composite technicians, welders, inspectors, manufacturing engineers, and quality personnel require experience and, frequently, customer-specific process qualifications. Rapid hiring raises training costs and can increase scrap or rework.

10. How to invest, and the outlook

Public routes. The listed menu spans risk/return profiles: aftermarket-heavy compounders (TransDigm, HEICO, Loar); build-rate and materials plays (Howmet, RBC Bearings, Hexcel); diversified multi-segment industrials (Curtiss-Wright, Woodward, Moog); small-caps (Ducommun, Astronics); and the diversified primes (RTX, GE Aerospace, Honeywell, Parker Hannifin) for whom parts are one line of a bigger story. For diversified exposure, aerospace-and-defense ETFs — the iShares U.S. Aerospace & Defense fund (ITA), Invesco Aerospace & Defense (PPA), and SPDR S&P Aerospace & Defense (XAR) — hold baskets of these suppliers. The trade-off is purity: the closer a company is to a complete, diversified aerospace portfolio, the less its reported results correspond to 336413; ETFs add aircraft OEMs, engines, missiles, electronics, and government-services businesses outside the code.

Private routes. Direct ownership of suppliers, co-investment alongside the sponsors now active in the space (Apollo, Warburg Pincus, Berkshire Partners), private-credit lending to leveraged suppliers, or — for the patient — Berkshire Hathaway shares as an indirect stake in Precision Castparts. The most important private diligence is conducted part by part and program by program: who owns the design and tooling; whether the part is sole-, single-, or dual-sourced; required FAA and customer approvals; remaining platform life; OEM versus aftermarket revenue; pricing-reset and material-escalator terms; customer-owned inventory; quality escapes; supplier qualification; backlog cancellation rights; capital required for rate increases; and normalized working capital.

Near-term drivers (forward-looking). The setup is structurally favorable: a record aircraft backlog above 17,000 jets [30], climbing build rates (737 toward 47/month, A320neo above 50) [27], and an aging in-service fleet feeding a ~$100 billion MRO and spares market [28]. The judgment call is twofold — Boeing's production execution remains the swing factor for OEM-levered suppliers, and years of strong performance have left the best aftermarket franchises trading at rich valuations, so the quality of the businesses is not in doubt but the price paid is. On balance, the industry combines the recurring, regulation-protected economics investors prize with real cyclical and execution risk beneath the surface.

---

Sources

1. NAICS Association / U.S. Census Bureau. "NAICS Code 336413 — Other Aircraft Parts and Auxiliary Equipment Manufacturing" (2022 definition, scope and exclusions). https://www.naics.com/naics-code-description/?code=336413
2. TransDigm Group Inc. "Form 10-K, Fiscal Year 2025" (revenue, operating margin, aftermarket mix, interest expense, product life cycle). https://www.sec.gov/Archives/edgar/data/1260221/000126022125000081/tdg-20250930.htm
3. Aerospace Industries Association. "Industry Impact — U.S. aerospace & defense exports and trade surplus" (2025). https://www.aia-aerospace.org/industry-impact/
4. U.S. Census Bureau. "2022 NAICS Definition — 336413" (official scope). https://www.census.gov/naics/?details=336413&input=336413&year=2022
5. U.S. Census Bureau. "2022 Economic Census — Concentration by Largest Firms, NAICS 336413" (receipts, firm count, CR4/CR8/CR20/CR50; HHI suppressed) (2022). https://www.census.gov/programs-surveys/economic-census.html
6. U.S. Census Bureau. "County Business Patterns, NAICS 336413" (establishments, employment, annual payroll) (2023). https://www.census.gov/programs-surveys/cbp.html
7. U.S. Small Business Administration. "Table of Small Business Size Standards" (2023). https://www.sba.gov/document/support-table-size-standards
8. U.S. Bureau of Labor Statistics. "Current Employment Statistics, NAICS 336413" (June 2025). https://www.bls.gov/ces/data/employment-and-earnings/2025/table1a_202507.htm
9. U.S. Department of Defense. "Financial Performance of Defense Contractors — Appendix G–J" (historical 2012 concentration data). https://www.acq.osd.mil/asda/dpc/pcf/docs/finance-study/DoD%20Study%20Appendix%20G%20-%20J.pdf
10. Boeing Company. "Boeing Completes Acquisition of Spirit AeroSystems" (December 8, 2025). https://boeing.mediaroom.com/2025-12-08-Boeing-Completes-Acquisition-of-Spirit-AeroSystems
11. Investing.com / Jefferies. "Top Aerospace Suppliers to Watch" — Howmet Aerospace revenue and 2026 guidance (2026). https://www.investing.com/news/stock-market-news/top-aerospace-suppliers-to-watch-according-to-jefferies-93CH-4750684
12. CompaniesMarketCap. "TransDigm / Howmet Aerospace / HEICO — market capitalization" (2026). https://companiesmarketcap.com/transdigm/marketcap/
13. Intellectia / TransDigm. "TransDigm acquisitions and FY2026 revenue guidance" (2026). https://intellectia.ai/news/stock/transdigm-tdg-acquires-two-aerospace-parts-companies-for-22-billion
14. Newswire / HEICO Corporation. "HEICO Reports Record Results for Fourth Quarter and Full-Year Fiscal 2025" (2025). https://www.newswire.com/news/heico-corporation-reports-record-net-income-up-35-on-record-operating-income-up
15. Moog Inc. "Moog Reports Record Fourth Quarter 2025 Sales" — FY2025 revenue (2025). https://www.moog.com/content/dam/moog/literature/Corporate/Investors/press-releases-pdf/2025/q4/Moog-Reports-Record-Fourth-Quarter-2025-Sales.pdf
16. Woodward Inc. "2025 Annual Report" (FY2025 net sales, aerospace segment margin). https://www.sec.gov/Archives/edgar/data/108312/000119312525317470/wwd_ars_2025.pdf
17. Macrotrends. "Curtiss-Wright Revenue 2010–2025" (2025). https://m.macrotrends.net/stocks/charts/CW/curtiss-wright/revenue
18. Hexcel Corporation. "Form 10-K, Fiscal Year 2025" (revenue, operating margin, supplier concentration, production model). https://www.sec.gov/Archives/edgar/data/717605/000119312526046377/hxl-20251231.htm
19. RBC Bearings Inc. "Fourth Quarter and Full-Year Fiscal 2025 Results" (Form 8-K) (2025). https://www.sec.gov/Archives/edgar/data/1324948/000121390025044635/ea024240001ex99-1_rbcbear.htm
20. Ducommun Inc. "Form 10-K, Fiscal Year 2025" (revenue, defense/commercial mix). https://www.sec.gov/Archives/edgar/data/30305/000162828026011952/dco-20251231.htm
21. Astronics Corporation. "Astronics Reports Record Aerospace Segment Sales in 2025 Second Quarter" (2025). https://investors.astronics.com/news-events/press-releases/detail/436/astronics-corporation-reports-record-aerospace-segment
22. StockAnalysis / CompaniesMarketCap. "Loar Holdings — revenue and market capitalization" (2025). https://stockanalysis.com/stocks/loar/revenue/
23. IndustryWeek. "Berkshire Hathaway to Buy Precision Castparts for $37 Billion" (2015; deal closed 2016). https://www.industryweek.com/supply-chain/article/21965706/berkshire-hathaway-to-buy-precision-castparts-for-37-billion
24. Triumph Group Inc. "Form 8-K — Completion of Acquisition" (July 24, 2025). https://www.sec.gov/Archives/edgar/data/1021162/000095017025098396/tgi-ex99_1.htm
25. Latham & Watkins. "Apollo Completes US$3.6 Billion Acquisition of Barnes Group" (2025). https://www.lw.com/en/news/2025/01/latham-watkins-advises-apollo-in-completed-us3-6-billion-acquisition-of-barnes-group
26. IB Interview Questions. "Engine OEMs and the Aftermarket MRO Business Model — razor-and-blades economics and aftermarket margins" (2025). https://ibinterviewquestions.com/guides/industrials-investment-banking/engine-oems-aftermarket-mro-business-model
27. Flight Plan / Forecast International. "Airbus and Boeing 2025 Production Rates and Deliveries" (2025). https://flightplan.forecastinternational.com/2025/11/02/airbus-and-boeing-october-2025-production-rates-and-unofficial-deliveries/
28. Oliver Wyman. "Global Fleet and MRO Market Forecast 2025–2035" (2025). https://www.oliverwyman.com/our-expertise/insights/2025/feb/global-fleet-and-mro-market-forecast-2025-2035.html
29. U.S. Federal Aviation Administration. "FAA Aerospace Forecast, Fiscal Years 2026–2046" (U.S. fleet, RPM growth). https://www.faa.gov/data_research/aviation/aerospace_forecasts/FY_2026-2046_Full_Forecast_Document_Tables.pdf
30. Market.us. "Commercial Aircraft Aftermarket Parts Market" (backlog, IATA supply-chain disruption cost) (2025). https://market.us/report/commercial-aircraft-aftermarket-parts-market/
31. U.S. Federal Aviation Administration. "Production Approvals Overview" (14 CFR Part 21). https://www.faa.gov/aircraft/air_cert/production_approvals
32. U.S. Federal Aviation Administration. "Parts Manufacturer Approval (PMA)" (2025). https://www.faa.gov/aircraft/air_cert/design_approvals/pma
33. U.S. Bureau of Industry and Security. "Export Administration Regulations (EAR)" (2025). https://www.bis.gov/regulations/ear
34. Aerospace Industries Association. "2024 Supply Chain Health Check" (critical materials, labor). https://www.aia-aerospace.org/wp-content/uploads/Supply-Chain-Health-Check.pdf