Aircraft maintenance is the backbone of airworthiness. From a weekend Cessna under Part 91 to an airline fleet under Part 121, staying compliant means understanding inspections, documentation, and who may perform what under the Federal Aviation Regulations (FARs). This 2025 guide distills the essentials—annuals and 100-hour inspections, MEL/KOEL logic, Airworthiness Directives (ADs), Service Bulletins (SBs), and the pilot–mechanic workflow—so you can keep your aircraft safe, legal, and ready to fly. When you want deeper how-tos and owner checklists, explore our in-house tutorials in Flight School Guides and Pilot Career Advice.
What “maintenance” means—and who may perform it
Under the FAA’s maintenance rule, 14 CFR Part 43, maintenance includes inspection, repair, preservation, and replacement of parts. Certificated mechanics (A&P) and Part 145 repair stations normally perform maintenance and return aircraft to service. Pilots may perform only preventive maintenance listed in Part 43 Appendix A(c) (e.g., replacing safety wire, servicing wheel bearings, changing spark plugs) and must make a proper logbook entry.
Required inspections for Part 91 operators (GA cheat sheet)
Annual inspection (every 12 calendar months): Required for most GA aircraft and must be signed off by an IA (A&P with Inspection Authorization).
100-hour inspection: Required if you carry persons for hire or provide instruction for hire in that aircraft. An A&P may sign it off; if overdue, you may only fly to a place where the inspection can be done.
Progressive inspections: Optional programs approved by FSDO to break the annual into phases—handy for flight schools.
IFR equipment checks: Altimeter/static under §91.411 (24 months), transponder under §91.413 (24 months), and ELT inspection/battery under §91.207.
Planning tip: Align the annual with your 24-month IFR checks to minimize downtime. For step-by-step owner planning and budgeting, see our Pilot Career Advice guides.
Airline & commercial maintenance in brief (Parts 121/135)
Air carriers operate under FAA-approved Continuous Airworthiness Maintenance Programs (CAMP), reliability programs, and detailed task cards built from Maintenance Review Board (MRB) reports and OEM manuals. Scheduled work is often grouped as A/B/C/D checks (terminology varies by operator). Part 135 operators adopt manufacturer programs or CAMP scaled to utilization. For how GA and business aviation plan inspections and reliability, explore Private & Business Aircraft.
MEL vs. KOEL vs. MMEL: what you can legally defer
Your AFM/POH includes a Kinds of Operations Equipment List (KOEL) describing what’s required for Day/Night and VFR/IFR. Many types also have a Master Minimum Equipment List (MMEL) from which operators create an aircraft-specific MEL. With an MEL, you may dispatch with certain items inoperative if you follow the placards, procedures, and time limits in §91.213. Without an MEL, use KOEL plus the rule’s “four-source” logic. The FAA’s MEL/MMEL overview is here: MEL Policy & Guidance. For practical dispatch decision trees and IFR readiness tips, see our Flight School Guides.
Airworthiness Directives (ADs) vs. Service Bulletins (SBs)
ADs are mandatory—they correct unsafe conditions and are legally enforceable. SBs are manufacturer recommendations (often wise to comply with, and sometimes incorporated into an AD). Maintain a dedicated AD log listing the AD number, subject, method of compliance, and next due across airframe, engine, propeller, and installed appliances. Start searches at the FAA AD Portal and the Dynamic Regulatory System (DRS). We walk through record-keeping and AD research step by step inside our Flight School Guides.
The technical data your mechanic relies on
Professional maintenance references approved/acceptable data such as the Aircraft Maintenance Manual (AMM), Illustrated Parts Catalog (IPC), Structural Repair Manual (SRM), Wiring Diagram Manual (WDM), and OEM Service Bulletins/Letters. Ask your A&P or MRO to cite the specific data (chapter/task) in log entries for complex work and keep copies with your records. That habit speeds future troubleshooting and impresses pre-buy inspectors.
Logbooks and return-to-service entries (what must be written)
Two rule anchors govern entries: §43.9 (maintenance/alterations) and §43.11 (inspections). Required elements include a description of work, reference to data used, date, total time if applicable, and the signature/certificate number of the person approving or not approving for return to service. Failed inspections must list discrepancies. Use our owner QA checklist in Pilot Career Advice to verify entries before you fly.
Planning an annual or 100-hour: owner’s checklist
- Collect records: Last annual/100-hour, AD status sheet, 91.411/91.413/91.207 cards, W&B, equipment list, STCs/Forms 337.
- Prioritize squawks: Describe each defect clearly (system, symptom, when it occurs, how to reproduce).
- Parts strategy: Ensure traceability (8130-3/COC when applicable) and order long-lead items early (tires, hoses, filters, ELT batteries).
- Corrosion watch: Focus on tailcones, battery boxes, lap joints, and bilge areas in coastal/humid climates.
- Post-maintenance acceptance: Plan a ground run, leak/ops checks, and if needed, a short acceptance flight with criteria agreed in advance. Download printable versions of this checklist in our Pilot Career Advice library.
How pilots and mechanics collaborate (from squawk to sign-off)
A precise write-up saves hours. Use a template like: System — Symptom — When — Repro steps — Indications. Example: “Electrical—Amps spike to 60 after takeoff—first noticed 05/10 at night—reproduces with landing lights ON—ALT light flickers.” Your A&P will translate this into troubleshooting steps, cite data (AMM/WDM), perform corrective action, and create a return-to-service entry referencing Part 43 and any AD/SB compliance. You’ll verify results on a controlled run-up and, if appropriate, a short acceptance flight. Keep a shared squawk log so repeat defects are obvious.
Common compliance pitfalls (and how to avoid them)
• Missed AD intervals: Keep a living AD spreadsheet with “Next Due” for recurring actions.
• IFR checks out of sync: Calendar reminders for 91.411/91.413 help prevent quiet expirations.
• Parts traceability gaps: Ask for 8130-3/COC where required and keep supplier invoices.
• Weak log entries: Ensure 43.9/43.11 elements and data references are present before you accept the airplane.
• Weight & balance drift: After avionics/interior changes, demand updated W&B and equipment list.
• Missing torque/seal details: Photograph critical items (brake lines, prop safety wire) for the file. For standardized acceptance checklists, see our Flight School Guides.
GA vs. transport: how inspection “packages” differ
General aviation uses annual/100-hour/progressive programs built from OEM schedules, ADs, and optional SBs.
Transport/airline maintenance bundles tasks into phased packages (A/B/C/D) driven by MRB methodology and reliability data. C checks open major access for structural and systems inspections; D-level (or equivalent heavy visit) is a deep structural event at multi-year intervals. For platform-specific differences (piston, turboprop, bizjet), browse Private & Business Aircraft.
Tooling, test equipment, and calibration
Accuracy depends on calibrated tools: torque wrenches, pressure gauges, micrometers, pitot-static testers, ignition analyzers. Request copies of altimeter/static test reports and transponder bench cards after each 24-month IFR check and file them with your logbooks. If you’re vetting a shop, confirm ratings and capabilities through the FAA’s Dynamic Regulatory System.
When to bring in a specialist
Structural repairs, composite layups, advanced avionics integration, and prop governor work often belong in specialized shops with fixtures and repairman authorizations. If you’re chasing chronic issues (e.g., high CHT, intermittent alternator trips, autopilot oscillation), consider an OEM service center or a Part 145 repair station with model-specific experience. You can search for repair stations and verify ratings via DRS.
FAQs (high-intent, U.S. readers)
What can a private pilot do as preventive maintenance? Only tasks listed in Part 43 Appendix A(c), with a proper log entry.
What’s the difference between an A&P and an IA? An A&P performs maintenance; an IA may perform and approve annual/major inspections and sign Form 337 major repairs/alterations.
Are Service Bulletins mandatory? Not unless referenced by an AD or required by your maintenance program, lease, or warranty.
Can I fly to a shop if my annual is expired? You may request a ferry permit (special flight permit) if the aircraft is safe for the intended flight—see FAA guidance on Special Flight Permits.
How do I know which ADs apply? Search the FAA AD Portal by airframe, engine, prop, and appliances and keep a signed compliance list on file.
Keep learning with Aviation Titans (internal links)
Build practical owner workflows in Flight School Guides, sharpen procedures with Simulator Technology, and compare platforms in Private & Business Aircraft. For fresh features and news, visit AviationTitans.com.
Bottom line
Staying safe and compliant in 2025 means mastering the rules (Part 43/91), records (43.9/43.11), and responsibilities shared by pilots, A&Ps, IAs, and repair stations. Build a predictable inspection calendar, keep an up-to-date AD/SB status sheet, document every return-to-service entry correctly, and collaborate with your mechanic using precise squawks and acceptance criteria. The payoff is measurable: fewer surprises, faster turnarounds, higher resale value—and most importantly, an aircraft you trust every time you advance the throttle.
