Process auditing is central to the aerospace quality management system. Under AS9100 Rev. D, it provides assurance that an organisation’s processes are implemented, controlled, and continually improved in line with customer and regulatory requirements. A process audit evaluates how work is done—whether inputs, controls, and outputs match planned arrangements—and whether the process consistently achieves its purpose. For special processes such as shot peening, whose results cannot be verified by later inspection, auditing is vital to guarantee structural integrity and fatigue performance.

The first stage of an effective audit is defining a clear scope and objective (AS9100 9.2.2). The scope sets the boundaries—for instance, the shot peening of turbine discs or the calibration of Almen gauges—while objectives describe what the audit seeks to confirm, such as compliance with AMS 2430, adherence to internal work instructions, and effectiveness of risk controls. Objectives should explicitly consider performance and risk: can the process consistently achieve the required compressive stress levels, and are potential sources of variation controlled? Setting such aims ensures the audit supports the organisation’s wider risk-based management approach.

Next, the auditor must understand the process context and ownership. Under Clause 4.4, every process must have a designated owner responsible for performance and risk management. In a shot-peening cell, this is usually the manufacturing engineer or production manager who oversees media control, machine parameters, and operator competency. The auditor should review the process flow, inputs (shot size, air pressure, part condition), and outputs (residual stress, Almen intensity, coverage). Understanding how these interrelate allows evaluation of whether controls are robust and monitoring is effective.

Good planning underpins a reliable audit. The audit plan should reference applicable standards and criteria—AS9100 clauses, AMS 2430, internal procedures, calibration and training records—and identify high-risk areas such as variation in shot flow or nozzle wear. AS9100 promotes risk-based thinking; auditors should therefore focus on points with the greatest impact on product conformity or safety. Verifying the calibration status of Almen gauges or correct generation of intensity curves, for example, is of higher priority than checking administrative details.

During the audit, objective evidence must be gathered through observation, documentation, and interviews. In shot peening, this may include watching operators set up machines, confirming that media classification and magnetic separation are performed, and checking process parameters against job sheets. Supporting evidence includes calibration certificates, maintenance logs, and control charts. The auditor also reviews whether risk controls are maintained—such as scheduled nozzle inspections, preventive maintenance, and closure of previous corrective actions. Interviews reveal whether operators understand both the purpose of peening and the consequences of deviating from procedure.

Evidence is then evaluated against the audit criteria (AS9100 9.2.1). The auditor determines whether the process conforms to planned arrangements and whether it is effective. A process can be compliant yet ineffective if it suffers from high rework rates or variable results. Effectiveness should therefore be judged alongside indicators such as Almen intensity stability, scrap rate, and first-pass yield. Data trends showing increased variability represent a risk to conformity and should trigger recommendations for preventive action. This aligns with the AS9100 principle that auditing supports proactive risk mitigation rather than reactive correction.

Findings must be recorded clearly and classified by severity and risk impact. A major nonconformity signifies a serious breakdown or risk to quality, such as uncalibrated equipment or use of the wrong shot media, while a minor one might relate to incomplete documentation. Opportunities for improvement may involve enhancing traceability, automating data capture, or tightening process limits. Each finding should reference the relevant clause or procedure and cite the supporting evidence objectively. The auditor’s role is to provide an evidence-based assessment, not assign blame.

Following AS9100’s focus on communication, the closing meeting presents findings to the process owner, ensuring mutual understanding and agreement on corrective actions. The written audit report should summarise the scope, criteria, evidence, and conclusions, linking findings to AS9100 clauses and assessing both conformity and effectiveness. In the shot-peening example, it might include comments on intensity-trend stability, media management, and the adequacy of operator training. Timely, factual reporting enables management to address issues before they escalate into product risk.

The follow-up stage confirms that corrective and preventive actions are completed and effective. Each nonconformity requires root-cause analysis using, for instance, the 5 Whys method, and must address underlying causes, not just symptoms. If an incorrect shot size was used because of poor labelling, actions could include revised identification, procedure updates, and refresher training. Verification of effectiveness—perhaps by auditing the same area after several production cycles—ensures lessons learned feed into the risk register and continuous improvement process, meeting AS9100 10.2 requirements.

Process auditing under AS9100 should be understood as a risk-based improvement tool, not merely a compliance check. For special processes like shot peening, routine auditing ensures parameters remain within validated limits, that process drift is detected early, and that any emerging risks—such as deterioration of air-pressure regulation or media contamination—are controlled before affecting parts. Over time, analysing audit data highlights performance trends that inform future risk reviews, guide preventive maintenance, and support management-review decisions.

In practice, effective risk-based auditing strengthens both compliance and performance. By linking audit planning to risk assessment, focusing evidence collection on critical controls, and ensuring corrective actions reduce underlying risk, the auditor helps sustain a controlled and reliable process. This approach supports the intent of AS9100: improved product conformity, enhanced customer satisfaction, and an embedded culture of continual improvement.

In conclusion, auditing a process such as shot peening correctly requires both technical understanding and adherence to AS9100’s principles of process ownership, objective evidence, and risk-based evaluation. A well-planned and executed audit confirms that the process is controlled, effective, and resilient to risk. More than demonstrating compliance, a risk-based process audit provides confidence that every shot-peened component will perform safely and consistently throughout its service life—a vital assurance in the aerospace sector.

Christian Tyroll, MFN Contributing Editor

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