What are Source Inspections?

A “Source Inspection“ is different from a “Supplier Audit” (or Product Audit) because it is an “inspection” (not an audit). Unlike a Supplier/Product Audit (which follows a product through its entire production process – verifying that requirements have been met), a Source Inspection either takes place at:

  • the end of the production line (e.g., inspecting a sampling of completed/finished parts/assemblies within a lot/batch or of a single part/assembly representative of the first production lot/batch (i.e., a First Article Inspection))
  • at a specific point in the process (i.e., an “in-process” inspection)
  • at an interim point (e.g., where a part resumes production after having been out of production for a specific period of time)

A “Source Inspection” typically involves verifying:

  • that the product characteristics comply with those specified on an Engineering drawing (along with any specifications invoked), and could also include non-destructive testing.
  • the raw material certifications (e.g., Certificate of Analysis, Material Test Reports) supports that the material used complies with the requirements for the finished product.
  • that any “Special Processes” are supported by certificates from the processing operation (whether in-house or outsourced). The Aerospace industry usually requires those special processes to be Nadcap accredited.

While a “Source Inspection” typically involves the Inspector personally performing the inspection activities, there are valid reasons for why an Inspector may instead, choose to “witness” a supplier's employee(s) performing the inspection activities. The most common reason for this is that the Inspector does not have the portable measuring instruments necessary for performing the inspection. While the Customer may require the Supplier to provide the necessary measuring instrumentation, this can introduce a liability (e.g., the Inspector inadvertently damaging the supplier's measuring instrumentation). Witnessing, rather than performing the inspection, greatly mitigates this liability.

Witnessing an inspection activity, rather than performing it, also provides some benefits. For example, witnessing the inspection(s) allows the “Source Inspector” to verify that the supplier's employee(s), whether production personnel or quality control inspectors - possess the knowledge, skills, and ability (KSA) to:

  • Read and understand applicable drawings/specifications (e.g., GD&T - Geometric Dimensioning and Tolerancing)
  • Verify correct raw material was used (e.g., through associated Material Test Reports, Chemical Analysis Reports)
  • Verify correct welding/brazing filler material was used (e.g., through associated Certified Material Test Reports)
  • Verify correct soldering material (solder wire, solder paste, solder bar) was used (e.g., lead-free solder vs. lead solder)
  • Availability and proper use of measuring instruments required for the inspection
  • Maintain an acceptable accuracy ratio (between the measuring instrument accuracy and the tolerance(s) being measured)
  • Verify consistency of any visual inspections with the specifications
  • Verify proper understanding and use of representative standards (e.g., visual inspections)


When a Source Inspection takes place at the end of the Production Line, it usually involves a much larger sampling (e.g., including parts/assemblies from multiple shifts and multiple workers) of finished products (based on the AQL or AOQL selected) than would be possible during a “Product Audit”. The AQL is the “Acceptance Quality Limit”… which is defined as the “quality level that is the worst tolerable process average” (Ref. ISO 2859-1:1999, sec. 3.1.26). The AQL is normally based on sampling tables contained in either the ASQ/ANSI Z1.4 or Z1.9 Standard. The AOQL is the “Average Outgoing Quality Limit” and is typically based on tables contained in the book ”Zero Acceptance Number Sampling Plans“, (Fifth Edition) by Nicholas L. Squeglia.

The most practical difference between choosing an AQL or AOQL is that the ASQ/ANSI Z1.4 & Z1.9 Standards allow a certain number of defective products to be identified in the sample, and the entire lot/batch can still be accepted. In contrast, when using the sampling approach described in the book ”Zero Acceptance Number Sampling Plans“, if a single defect is found, then the entire lot/batch must be rejected and undergo a 100% inspection.

First Article Inspection

A First Article Inspection (FAI) takes place at the end of the production process consisting of a single part/assembly representative of the first production lot/batch. Whether or not the part/assembly is an aerospace product, it is recommended to utilize the AS9102 standard and its associated forms.

Unlike a “First Article Inspection Report” (FAIR), most “Source Inspection” reports would include the results of all of the products inspected (i.e., included in the sample).

Preparing for a Source Inspection

When scheduling an Inspector to visit a supplier for a “Source Inspection”, the following information should be provided to the Inspector:

  1. Supplier contact name, phone number, and e-mail address
  2. Purchase Order Number (or a copy of the applicable Purchase Order)
  3. Item Number
  4. Part Number & Revision Level
  5. A copy of the applicable Drawing(s) and/or Specifications
  6. Quantity of parts to be inspected (or a specified AQL or AOQL)
  7. Date source inspection is required
  8. Type(s) of inspection required
    • In-Process (identifying the specific point in the process where the inspection should be performed)
    • Final
    • Interim (i.e., a period of time between events)
    • First Article Inspection (FAI)

An Inspector will often choose to take portable measurement instruments, with a known calibration status, to the supplier site. If larger equipment is required, then the Inspector would need to either use or witness an employee, performing the measurements using the measuring instruments owned by the supplier. These arrangements should be made in advance.

In addition, when measurement instruments owned by the supplier are used for the source inspection, the Inspector “should” verify that the supplier has maintained their calibration status throughout the production lot/batch.


Where a sufficient sample size has been taken, the “Source Inspection” results “may” be used as justification for parts/assemblies to bypass any Receiving Inspection process (as this has already been performed at the supplier's site).

And where nonconformities are identified during the “Source Inspection” these issues can be addressed prior to parts/assemblies leaving the supplier's facility. In addition to reducing time and transportation expenses, it also allows for the supplier to correct its processes to better ensure that only conforming product is produced.