Understanding Boeing BAC Aircraft Part Numbers
BAC part numbers are used throughout Boeing aircraft documentation for proprietary standard parts, hardware, structural items, and manufacturing requirements. This guide explains where BAC numbering came from, how BAC part numbers are generally organized, what common letter families can indicate, and why the complete Boeing-approved reference must be checked before ordering.
What Does “BAC” Mean?
BAC is associated with Boeing aircraft standards and proprietary Boeing part-number families. In aircraft maintenance and supply records, BAC-prefixed numbers may identify Boeing-controlled hardware, structural components, fittings, fasteners, materials, or process specifications.
BAC parts are different from industry-wide standards such as AN, MS, NAS, or NASM. A BAC item may function as a standard part across multiple Boeing aircraft or assemblies, but the design and controlling data remain within Boeing’s product-standard system.
BAC Is Not the Same as AN, MS, or NAS
AN, MS, NAS, and NASM standards were developed under government or industry standardization systems. BAC numbers are Boeing-controlled identifiers. A BAC part should be verified using Boeing-approved technical data, product standards, aircraft manuals, or authorized cross-reference information.
- Do not assume a BAC part is universally interchangeable with an AN, MS, NAS, or commercial item.
- Do not decode the complete part from the BAC prefix alone.
- Confirm the exact Boeing aircraft, assembly, and effectivity when applicable.
- Review current Boeing data before accepting an alternate or superseding number.
Why Boeing Developed BAC Standards
Aircraft manufacturers need controlled parts and processes that can be applied consistently across engineering, production, maintenance, procurement, and supplier quality systems.
Design Control
BAC standards allow Boeing engineering to define the exact geometry, material, finish, strength, inspection, and installation requirements for a part.
Common Boeing Hardware
A controlled BAC family can support repeated use of the same hardware design across multiple Boeing assemblies or aircraft programs.
Supplier Consistency
Boeing suppliers can manufacture or process parts to a common product standard rather than relying only on individual assembly drawings.
Fleet Support
Stable Boeing part-number families help airlines, MROs, distributors, and maintenance teams support aircraft over long service lives.
How a BAC Part Number Is Generally Organized
BAC part numbers do not all follow one universal decoder. Different Boeing product-standard families use different layouts. A complete number may contain the BAC prefix, a family letter, a standard identifier, dash-controlled dimensions, and additional material or configuration codes.
BAC + FAMILY + STANDARD + DASH OPTION
This is a general concept only. The actual meaning of each character must be confirmed using the controlling Boeing product standard or approved aircraft documentation.
Common BAC Letter Families
BAC numbers often include a letter after the BAC prefix that helps identify the broad product family. Exact meanings and numbering rules must still be confirmed in Boeing data.
BACB — Bolts and Related Fasteners
BACB families are commonly associated with Boeing bolts and bolt-type fasteners used in structural and mechanical aircraft assemblies.
- Structural and close-tolerance fastening
- Diameter, length, grip, head, drilling, and material may vary
- Oversize and special configurations may exist
BACN — Nuts and Nut Hardware
BACN families are commonly associated with nuts, anchor nuts, nutplates, and related Boeing fastening hardware.
- Fixed, floating, self-locking, or special nut applications
- Thread, material, temperature, and locking style matter
- Mounting pattern and configuration must be verified
BACW — Washers and Washer-Type Parts
BACW families are commonly associated with washers, shims, spacers, or washer-type Boeing standard parts.
- Load distribution and controlled spacing
- Inside diameter, outside diameter, and thickness may be encoded
- Material and hardness can be application-critical
BACR — Rivets and Rivet-Type Fasteners
BACR families are commonly associated with rivets and related permanent fastening systems used in Boeing structures.
- Sheet-metal and structural fastening
- Head style, diameter, length, alloy, and condition may vary
- Installation method must match approved data
BACC — Clamps, Connectors, and Related Families
BACC prefixes may appear across several Boeing-controlled component families. The remaining letters and base number are essential for identifying the actual product type.
- May include clamps, electrical items, or other component groups
- Do not identify the item from “BACC” alone
- Use the complete number and controlling standard
Other BAC Families
Boeing uses many additional BAC letter groups for fittings, pins, bushings, screws, seals, brackets, materials, and special product standards.
- Letter families are not a complete decoder
- Product-standard access may be required
- Aircraft manuals can provide effectivity and installation context
BAC Part Numbers vs. BAC Process Specifications
Not every BAC number is a physical part number. Boeing also uses BAC designations for process and manufacturing specifications. A BAC process specification may define requirements for cleaning, coating, heat treatment, chemical processing, sealing, painting, inspection, additive manufacturing, or another manufacturing operation.
Before treating a BAC number as an orderable item, confirm whether it identifies a physical part, a material, a product standard, or a process specification. Same prefix, wildly different job—because aviation numbering apparently enjoys keeping buyers humble.
What Each Part of a BAC Number Can Change
A one-character or one-dash difference can identify a different size, material, finish, strength, configuration, or aircraft application.
| Number Element | What It May Identify | Why It Matters |
|---|---|---|
| BAC Family Prefix | The broad Boeing-controlled product or specification family. | A similar prefix may still contain multiple unrelated product groups. |
| Base Standard Number | The exact Boeing product standard, drawing family, or process specification. | A nearby number may identify a completely different part or process. |
| Dash Number | Diameter, length, grip, thickness, thread, angle, size, or another family-defined option. | The dash number often controls the physical fit of the part. |
| Material or Strength Code | Alloy steel, corrosion-resistant steel, aluminum, titanium, or another material or strength class. | Material affects strength, weight, corrosion, temperature, and compatibility. |
| Finish or Coating Code | Plating, passivation, anodizing, primer, sealant, lubricant, or another finish. | Finish affects corrosion resistance, torque, bonding, and environmental performance. |
| Configuration or Oversize Code | Drilled head, drilled shank, oversize diameter, special grip, locking feature, or another design option. | The exact option must match the approved assembly and repair data. |
BAC Compared with Industry Standards
BAC parts may resemble hardware covered by AN, MS, NAS, NASM, AS, or commercial standards, but appearance does not establish interchangeability.
- BAC is Boeing-controlled.
- AN and MS are government legacy standards.
- NAS and NASM are aerospace-standard systems.
- A Boeing-approved cross-reference is needed before substitution.
Why BAC Numbers Remain Common
Boeing aircraft remain in service for decades, and BAC product standards continue to support production, modification, maintenance, and repair.
- Used across Boeing commercial and defense aircraft records
- Common in illustrated parts catalogs and maintenance documentation
- Used by Boeing-approved suppliers and repair organizations
- Important for effectivity, configuration, and structural repair control
Similar BAC Numbers Are Not Automatically Interchangeable
Two BAC numbers can look nearly identical while representing different grip, diameter, material, finish, oversize, drilling, head style, strength, or configuration requirements.
- Verify the complete BAC number from current Boeing-approved data.
- Confirm aircraft model, assembly, location, and effectivity when applicable.
- Review all dimensions, material, finish, and configuration codes.
- Do not substitute from appearance, partial numbers, or an unverified seller cross-reference.
Where BAC Parts Are Used
- Boeing airframe structural joints
- Wing, fuselage, empennage, and control-surface assemblies
- Landing gear, doors, fairings, and access panels
- Flight-control and mechanical linkages
- Electrical, hydraulic, fuel, pneumatic, and environmental systems
- Interior, equipment, engine, and accessory mounting
What to Review Before Ordering
- Complete BAC number, including every letter, dash, and suffix
- Aircraft model, effectivity, assembly, and installation location
- Dimensions, grip, material, finish, strength, and configuration
- Condition, quantity, and unit of sale
- Manufacturer CoC, Company CoC, trace, labels, or other documentation
- Approved Boeing alternate, supersession, or repair data
How to Search for BAC Parts
Search the full BAC number first, including every letter, leading zero, dash, and suffix. BAC numbers are often long, and dropping one character can return a related but incorrect part.
If the exact number does not return a result, search the base family to locate related inventory—but treat those results only as leads. Final identification should come from Boeing-approved product standards, the illustrated parts catalog, structural repair manual, maintenance manual, engineering data, or another accepted technical source.
Need Help Identifying a BAC Part?
Send AVBOX US the complete BAC number, Boeing aircraft model, assembly location, photographs, alternate number, dimensions, or documentation requirement you are working through.