NADCAP Certification for Deep Hole Drilling: Complete Guide to Aerospace Special Process Accreditation

NADCAP — the National Aerospace and Defense Contractors Accreditation Program — is the accreditation standard for “special processes” in the aerospace industry. It is managed by the Performance Review Institute (PRI) and required by every major aerospace OEM including Airbus, Boeing, GE, Pratt & Whitney, Rolls-Royce, and Safran.

For deep hole drilling operations serving the aerospace industry, NADCAP accreditation is not optional — it is a contractual requirement. A deep hole drilled component in a landing gear actuator, flight control hydraulic cylinder, or turbine shaft is a safety-critical feature. The aerospace OEMs require independent verification that the drilling process is controlled, documented, and repeatable.

This guide covers the NADCAP requirements most relevant to deep hole drilling operations, including the audit process, required documentation, preparation timeline, cost, and common pitfalls.

What Is a Special Process?

NADCAP defines a special process as a manufacturing process where the result cannot be fully verified by subsequent inspection or testing. The quality of the output depends on the correct execution of the process itself, not on post-process inspection.

Deep hole drilling may be classified as a special process when:

• The bore geometry prevents complete inspection (extreme L/D ratio, small diameter, complex internal features)
• Surface integrity requirements cannot be verified by non-destructive methods alone
• The customer contract or specification designates deep hole drilling as a special process
• Guide pad burnishing affects surface integrity in ways that cannot be inspected non-destructively

NADCAP Commodity Codes Relevant to Deep Hole Drilling

For most deep hole drilling operations, AC7126 (Conventional Machining as a Special Process) is the applicable standard. If the operation includes EDM or laser drilling, AC7116 (Nonconventional Machining) applies.

Prerequisites

Before applying for NADCAP accreditation, the facility must meet the following prerequisites:

AS9100 Certification

A valid AS9100D (or AS9100 Rev C) quality management system certification is mandatory before NADCAP application. ISO 9001 alone does not qualify. AS9100 provides the quality system foundation — document control, internal audit, management review, corrective action — that NADCAP builds upon with process-specific requirements.

If the facility does not hold AS9100, an alternative path is available through the AC7004 audit, which serves as a quality system baseline assessment. This is typically used by facilities that are not seeking full AS9100 certification but need NADCAP accreditation for a specific process.

Production History

The facility must have been running the special process for at least three consecutive months with complete, real-time production records. Back-filling records is not permitted. The audit will review records from the three months preceding the audit date.

Personnel, Equipment, and Materials

• Operators must be trained and certified for the specific process
• Equipment must be calibrated to A2LA or CNAS-certified standards
• Materials must be aerospace-grade with full certification traceability

The NADCAP Audit Process

Phase 1: Preparation (2–4 Months)

Step 1 — Define the certification scope. Determine which NADCAP commodity codes apply to the facility’s operations. For a deep hole drilling shop, this is typically AC7126 (Conventional Machining). If the shop also performs EDM drilling or laser drilling, AC7116 (Nonconventional Machining) may also apply.

Step 2 — Download the audit criteria from the PRI website or eAuditNet (EAN platform). The audit criteria checklist (AC document) contains every requirement that the auditor will check. Each item on the checklist must be addressed in the facility’s documentation.

Step 3 — Create process-specific documentation. Build on the existing AS9100 quality system foundation. Required documents include:

• Process specifications (parameters, steps, equipment requirements)
• Personnel qualification records and certification matrix
• Equipment calibration, maintenance, and verification records
• Real-time production records, inspection records, non-conformance reports
• Internal audit reports against the AC checklist

Step 4 — Conduct internal audits and close gaps. Perform at least two full mock audits against the specific AC checklist before the official audit. Identify and close all gaps between current operations and NADCAP requirements. Many first-time applicants engage a consultant for a pre-audit mock assessment.

Step 5 — Register on eAuditNet (EAN). Complete company registration on the official PRI portal. Provide accurate company details — scope changes after submission delay the process.

Phase 2: Application (1–2 Months)

Step 6 — Submit certification application. Select the process and “initial certification” application type on EAN. Upload company qualification documents, system documentation list, and self-assessment report. PRI reviews and issues a formal quotation.

Step 7 — Confirm quotation and schedule. Pay the fees to confirm the application. PRI assigns a NADCAP-registered auditor and schedules on-site dates. Scheduling typically takes 2–6 months from application, depending on auditor availability.

Phase 3: On-Site Audit (2–5 Days)

The on-site audit covers four main areas:

Document compliance: Are system and process documents aligned with NADCAP criteria and under version control? Are customer specifications flowed down into work instructions?

Live operations observation: Does the practice on the shop floor match the documented procedures? The auditor will observe an actual deep hole drilling operation and verify that the operator follows the written process specification.

Record integrity: Are all production, inspection, and maintenance records complete, real-time, and traceable? Records must show actual values (not “within spec” checkmarks), and errors must be corrected per the documented correction procedure (single line-out, initialed, dated).

Process control: Are critical control points (coolant pressure, cutting speed, feed rate, tool condition) managed and monitored? Are non-conformances properly documented with root cause analysis?

Phase 4: NCR Closure (1–3 Months)

The auditor issues Non-Conformance Reports (NCRs) for any findings. Findings are classified as:

Each NCR requires a formal response containing five elements:

1. Immediate corrective action — actions taken to stop the nonconformance, including product impact assessment and customer notification
2. Root cause analysis — using a structured method such as 5-Why. Root causes should not be simplified to “operator error”
3. Impact assessment — identification of all products potentially affected by the root cause
4. Preventive actions — long-term corrective actions to prevent recurrence
5. Objective evidence — training records, procedure changes, or other documentation proving the corrective action

Phase 5: Certification Decision (1–2 Weeks)

The NADCAP task group — consisting of OEM representatives and industry experts — reviews the full audit package, including the auditor’s report and NCR closure evidence. If approved, the certificate is issued and the facility is added to the Qualified Manufacturers List (QML). Certificate validity is 12–24 months, renewable through surveillance audits.

Required Documentation for AC7126 (Conventional Machining)

System-Level Documents

Process-Specific Documents

Last 3 Months of Production Records

The auditor will review records from the three months preceding the audit date. These must be real-time records — no back-filling is permitted.

Cost and Timeline

Common Pitfalls

Starting Without AS9100

ISO 9001 is not sufficient. AS9100 certification is a NADCAP prerequisite. If the facility does not have AS9100, budget for either obtaining AS9100 first or undergoing the AC7004 baseline audit.

Incomplete or Back-Filled Records

Records must be real-time. Back-filling records to meet the three-month production history requirement is a common reason for audit failure. The auditor can detect patterns in record entries that suggest batch recording rather than real-time entries.

File-to-Floor Mismatch

The documented process specification must exactly match what happens on the shop floor. If the operator follows a different procedure than the one written in the SOP, this is a finding. Conduct mock audits where the auditor observes an actual operation and compares it to the written specification.

Inadequate Root Cause Analysis

Root cause analysis that stops at “operator error” is unacceptable. NADCAP auditors expect structured root cause analysis using methods such as 5-Why, fishbone diagrams, or fault tree analysis. The root cause should identify the system failure that allowed the operator error to occur.

Uncalibrated or Expired Measurement Equipment

All inspection equipment must be calibrated to A2LA or CNAS standards. Calibration certificates must cover the full operating range of the instrument. Expired calibrations are a major finding.

Expired Personnel Certifications

Operator certifications must be current. Establish a certification renewal tracking system and maintain backup certified staff.

Maintaining NADCAP Certification

After initial certification, ongoing compliance requires:

• Annual surveillance audits — typically 1–2 days, focused on high-risk areas from the previous audit
• Continuous real-time record keeping — the same documentation standards apply between audits
• Internal audits against the AC checklist — at least annually
• Change notification — significant changes to the process, equipment, or facility location must be reported to PRI
• Corrective action on all non-conformances — including those found during internal audits

Certificate validity is 12–24 months. Facilities with consistently good audit results may qualify for extended intervals.

NADCAP for Deep Hole Drilling Shops: Specific Considerations

What the Auditor Will Look For

In a deep hole drilling operation, the auditor will focus on:

• Process parameters — are coolant pressure, cutting speed, and feed rate specified on the work instruction? Are they recorded during production? Are corrective actions defined for deviations?
• Tool management — is there a system for identifying tools (by serial number or RFID)? Are regrind records maintained? Is tool life (maximum holes per edge) established and enforced?
• Coolant control — is coolant type and concentration specified? Are concentration checks, pH tests, and filter maintenance performed on schedule?
• Machine maintenance — are spindle runout, guide bush condition, and coolant system maintenance performed per the maintenance plan?
• Inspection — are bore diameter, surface finish, straightness, and roundness measured per the control plan? Are inspection instruments calibrated?
• Non-conformance handling — are out-of-specification bores documented with root cause analysis? Is the customer notified per contract requirements?

Common NCRs for Machining Operations

Based on published NADCAP audit data, the most common findings for machining operations include:

For related reading, see the Deep Hole Drilling Quality Standards Guide, the AS9100 Quality Management Guide, and the Bore Quality Inspection for Deep Hole Drilling Guide.