What Is Aircraft Structural Repair? A Guide to Major vs. Minor Alterations (and Repairs)
Guide to aircraft structural repair: major vs. minor, SRM/OEM/DER data, Part 145 controls, NDT, and shop vs. AOG—so you return to service safely and compliantly.
This article takes you from incident to RTS (Return-to-Service) safely and compliantly using SRM (Structural Repair Manual), OEM (Original Equipment Manufacturer), or DER (Designated Engineering Representative) data. If damage is beyond SRM or on primary/pressurized structure, we treat it as major. No data, no repair—Part 145 controls, NDT (Non-Destructive Testing) before/after, full traceability. Shop vs. AOG (Aircraft on Ground) as specs allow.
Definition: What “Structural” Really Means on an Aircraft
From the perspective of a repair station, aircraft structural repair means restoring load‑bearing airframe elements to an airworthy condition under approved data and documented processes. Structural parts carry flight or landing loads, maintain pressure, stiffness, and geometry—think fuselage skins/frames, wing spars/boxes, ribs, floor beams, empennage members, control surfaces and their attachments. If damage affects load paths, pressurization, alignment, or control geometry, it’s structural.
A compliant structural repair connects five things: assessment (visual + NDT), approved data (SRM/OEM/DER), controlled materials & processes, qualified personnel, and traceable documentation through Return‑to‑Service. Any weak link, and the job won’t pass the audit—or stand up in service.
Primary vs. Secondary Structures (Fuselage, Wings, Controls)
Primary: wing spars/box, pressure bulkheads, fuselage frames/skins, gear attach structure—highest scrutiny, rigorous data and NDT.
Secondary: fairings, access panels, non‑critical brackets—still controlled, but with more flexibility when allowed by data.
Major vs. Minor: Repairs and Alterations
Minor vs. Major is about the effect on safety/airworthiness and the extent of engineering/approval required.
Minor Repair: Fits within published limits (e.g., SRM) with no appreciable effect on weight, balance, strength, performance, powerplant operation, or flight characteristics. Documentation is still required, but the path is straightforward.
Major Repair: Goes beyond those limits or could affect the aircraft’s safety characteristics. It requires approved engineering data (OEM engineering, engineering order, or DER‑approved repair), specific process controls, and more extensive inspection/records.
Minor Alteration: Small configuration change that doesn’t appreciably affect the above factors and can be done with standard data and processes.
Major Alteration: A configuration change that could affect structural strength, aerodynamics, or systems integration. It typically needs approved engineering (OEM or DER) and may require additional approvals and documentation beyond a standard repair.
In practice: if damage or a proposed change exceeds SRM limits, alters load paths, or touches pressurized/primary structure, we treat it as major until engineering proves otherwise. For “replace‑only” OEM guidance, DER repairs often provide a safe, compliant alternative to full replacement.
Common Structural Damage (Bird/Lightning Strikes, Corrosion, Gear‑Up…)
Typical events we triage at a repair station:
Bird strikes/FOD: dents and tears at leading edges, cracked ribs/frames.
We map damage with visual measurement and NDT: eddy current for cracks/holes in aluminum, ultrasonic for composite delamination, X‑ray where geometry hides details, dye‑penetrant for open‑surface cracks, and mag‑particle for ferrous parts. Good mapping decides minor vs. major and SRM vs. OEM vs. DER.
Shop Repair vs. Mobile AOG: Picking the Right Setting
Shop (hangar) repair when you need:
Tight environmental control (composite cures, precision machining).
Complex access, jigs/fixtures, or deeper tear‑down.
Extensive hidden‑damage checks.
Mobile AOG when you have:
Field‑suitable scope with data that supports portable processes.
Strong logistics (parts/NDT staged) to cut downtime.
Environmental controls that still meet process requirements.
We run 24/7 AOG for structural events, but the real skill is knowing what not to do on the ramp. If a job needs hangar‑grade controls, we move it—quality and compliance come first.
DER Repair vs. OEM Replacement (and Alterations)
DER can provide approved engineering that restores strength/stiffness/durability when OEM documents point to replacement or when an alteration is needed. This is common for legacy fleets or out‑of‑limit damage.
Where DER shines: out‑of‑limit damage near SRM thresholds, legacy parts with long lead times, tailored reinforcements.
What stays constant: compliance, process rigor, and documentation—DER is not a shortcut, it’s an approved data path.
Choosing a Qualified Repair Station (Checklist)
Certification: Part 145 (or equivalent) with structural scope.
Engineering: Access to DER and strong OEM channels.
NDT: Methods and qualifications aligned to your materials and damage class.
Materials control: lot traceability, shelf‑life management, calibrated tools.
Process discipline: documented work cards, environmental/cure logs, torque/fastener records.
Documentation: clean RTS packages (e.g., 8130‑3/Form 1 where applicable).
AOG capability: genuine 24/7 response with field‑ready controls.
Service Commitments (Qualitative SLA)
Availability: 24/7 contact with an on‑call structures lead.
First Response: A qualified structures technician/engineer acknowledges the event and confirms next steps.
Triage Package: You receive a written triage summary (classification likelihood, proposed data path, recommended setting).
Execution Controls: Work only proceeds on approved data; every step documented on signed work cards.
RTS Documentation: Complete, audit‑ready RTS package delivered at release (including forms applicable to your jurisdiction).
Escalation Path: Named engineering authority (incl. DER access) for out‑of‑limit or replace‑only scenarios.
Procurement Checklist (Evidence‑Based)
Certifications/Approvals: Part 145 scope incl. structures; list available on request.
Engineering Access: Named DER disciplines (structures/composites).
NDT Capability: Methods available in shop and field; Level qualifications.
Materials Control: Lot traceability, shelf‑life tracking; example traveler/work card.
AOG Readiness: On‑call roster and mobilization checklist (no times promised).
Data Governance: Process for SRM/OEM/DER selection and approval retention.
FAQs
Is this a repair or an alteration—and when is it major? A repair restores damaged structure; an alteration changes configuration. It’s major when it can appreciably affect weight, balance, strength, performance, or flight characteristics—or when it exceeds standard data limits.
Do minor repairs ever become a major mid‑job? Yes—hidden damage or geometry changes can bump the classification. We re‑baseline engineering and approvals when that happens.
Are DER repairs or alterations “less safe” than OEM solutions? No. DER provides approved engineering data meeting regulatory standards. Execution and documentation are what make it safe and audit‑ready.
When is mobile AOG appropriate for structural work? When approved data and process controls can be met in the field without compromising quality or traceability. Otherwise, it’s a shop job.
Conclusion
As a repair station, our job is to take you from event to airworthy with the right classification (minor/major, repair or alteration), the right approved data (SRM/OEM/DER), and uncompromising process control. Whether we’re on the ramp at 02:00 or in a controlled hangar, the outcome should be the same: a repair or alteration that’s invisible in flight and impeccable on paper.
Rethink Repairs. Reclaim Your Budget.
Explore how MRO services and DER Repairs from DAS can reduce costs, speed up turnaround, and extend component life—without compromising safety or compliance.
.png)
%201.png)
%201.png)