Part 91 maintenance: what you have to track, and how to stay ahead of it.
A plain-English guide to the inspections, ADs and records that keep a Part 91 aircraft airworthy, written by a pilot and engineer. Use it as a checklist, then let MRO Tracker do the remembering.
The owner is responsible
Under 14 CFR 91.403, the owner or operator is primarily responsible for keeping the aircraft airworthy, including complying with airworthiness directives. Your mechanic does the work and signs for it. You are the one who has to know what is due.
Part 91 comes with no operations specifications and no one assigned to remind you. That freedom is the point of Part 91, and it is also why things slip.
The recurring inspections
Annual inspection
Required within the preceding 12 calendar months (91.409(a)), done by an A&P with Inspection Authorization or a repair station.
100-hour inspection
Only if the aircraft carries a person for hire, or you provide it for flight instruction for hire (91.409(b)). You may run up to 10 hours over to reach a place where the inspection can be done, and that time counts toward the next 100.
Turbine and large aircraft
Large airplanes, multiengine turbojets and turboprops, and turbine rotorcraft follow an inspection program you select under 91.409(e) and (f), such as the manufacturer's current program or an approved aircraft inspection program, instead of the annual and 100-hour. A progressive inspection under 91.409(d) is another approved option.
The other recurring checks
Altimeter, static system and altitude reporting: every 24 calendar months to fly IFR in controlled airspace (91.411)
Transponder: every 24 calendar months (91.413)
ELT: inspected every 12 calendar months, battery replaced after 1 hour of cumulative use or half its useful life (91.207)
VOR check: within the preceding 30 days for IFR, if you navigate by VOR (91.171)
A calendar month runs to the end of the month: an annual signed on March 3 is good until March 31 the next year.
ADs, service bulletins and TBOs
Airworthiness directives are mandatory
Each AD under 14 CFR Part 39 applies to an airframe, engine, propeller or appliance by model, often by serial number, and many recur by hours or calendar time.
Service bulletins usually are not
Under Part 91, a service bulletin is the manufacturer's recommendation unless an AD requires it or it is part of an inspection program you have to follow.
TBO is a recommendation for most
For most Part 91 operations, an engine can run past TBO if it is airworthy. Your insurer, a buyer and the next inspection will still ask about it.
Airworthiness limitations are hard limits
The Airworthiness Limitations section of the manual is mandatory (91.403(c)), including the life limits it sets.
Not mandatory is not the same as not important. Track bulletins and TBOs next to your ADs, so a decision to defer is made on purpose.
The records you must keep
Under 91.417, records of maintenance, preventive maintenance, alterations and required inspections are kept until the work is repeated or superseded, or for one year.
These records stay with the aircraft and go with it when it is sold:
Total time in service of the airframe, each engine, each propeller and each rotor
Current status of life-limited parts
Time since last overhaul of items overhauled on a time basis
Current inspection status, including time since the last required inspection
Current AD status: AD number and revision date, method of compliance, and the next due time and date for recurring ADs
Copies of Form 337 for major alterations
Each logbook entry under 14 CFR 43.9 needs a description of the work, the completion date, and the name, signature, certificate number and certificate type of the person approving the return to service. As a certificated pilot-owner you may do the preventive maintenance listed in Part 43 Appendix A and sign for it yourself.
When something is inoperative
Under 91.213 there are two ways to fly with inoperative instruments or equipment.
With an MEL. A Part 91 MEL needs a letter of authorization from your FSDO. You defer the item under the MEL's conditions and keep track of when it has to be fixed.
Without an MEL. For most non-turbine aircraft, confirm the item is not required by the type certificate, the equipment list, 91.205 or an AD. Then remove it, or deactivate it and placard it "Inoperative", and have a pilot or mechanic decide it is not a hazard.
Either way, write it up. An open item belongs in the discrepancy log until it is fixed.
Records to review before you buy
Complete logbooks for the airframe, engines and propellers, with no gaps
An AD compliance list showing how and when each AD was met
Form 337s and STCs that match what is installed, with the weight and balance and equipment list updated
Status of life-limited parts and time since overhaul
Damage history
The last annual, or the inspection program status, and any open squawks
Engine and propeller overhaul records and any trend data
Missing records cost money. A part with no history may have to be overhauled or replaced before the aircraft can go back into service.
How MRO Tracker keeps track for you
One due list for everything above
Annual, 100-hour, ELT, transponder, static, VOR and recurring AD presets, with limits by hours, calendar and cycles, whichever comes first. Hours and landings add up from each flight.
ADs found daily
New US ADs are checked every day and matched to your aircraft, engines, props and APUs. You review each match before it is tracked.
Squawks to closure, logbook entries without retyping
Write-ups go to the discrepancy log and stay open until fixed. Finished work prints as a 6 × 4 in logbook label with 43.9 or 43.11 wording.
Bring your spreadsheet
Import your current due list from Excel or CSV and the next due points are worked out for you.
Three aircraft or fewer? MRO Tracker Light is $275 a year for up to 3 aircraft and 2 users, with free read-only seats for your A&P. Start with Light
Larger fleet? Maintenance is $95 per aircraft a month ($150 for jets). MRO Tracker for Part 91 · See pricing
Common questions
Does a Part 91 aircraft need a 100-hour inspection?
Only if it carries a person for hire or is provided for flight instruction for hire. Otherwise the annual covers it, unless the aircraft is on an inspection program under 91.409(e).
Do I have to comply with service bulletins?
Not unless an AD requires it or your required inspection program includes it. Many owners comply anyway when a bulletin addresses safety or affects resale.
Can I fly past engine TBO?
For most Part 91 operations, yes, if the engine is airworthy. TBO becomes a limit when an AD, the Airworthiness Limitations section or your required inspection program makes it one.
What maintenance can I do myself?
A certificated pilot who owns or operates the aircraft may do the preventive maintenance listed in Part 43 Appendix A, and record it under 43.9, on aircraft not used under Part 121, 129 or 135.
How long do I keep maintenance records?
Routine work records until the work is repeated or superseded, or for one year. Total time, life-limited parts, overhaul times, inspection status, AD status and Form 337s stay with the aircraft.
What does 12 calendar months mean?
The period ends on the last day of the month. An annual done on March 3, 2026 is due by March 31, 2027.
This guide is a summary for planning, not legal or maintenance advice. Check the current regulations, your aircraft's manuals and your mechanic before relying on it.
Flying for hire or running a shop? See the Part 135 and Part 145 guides.
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