How to Read Aircraft Logbooks: A Visual Guide

An aircraft’s logbooks are its maintenance history, written by the people who did the work. When a jet is bought, financed, leased or inspected, someone reads them to answer a plain question: what was done to this aircraft, when, and who signed for it?

This guide follows one invented midsize jet through its records. It covers what sits on the records shelf, how to read a single entry, how work orders and 8130-3 tags back that entry up, and how Airworthiness Directives differ from service bulletins. Most figures are interactive, and a 12-question quiz at the end checks what stuck.

What the FAA requires you to keep

The owner’s recordkeeping rule, 14 CFR 91.417, splits an aircraft’s records into two groups.

The first group is the record of each job: a description of the work, the date it was finished, and the signature and certificate number of the person who approved it. The rule lets an owner discard these once the work is repeated or superseded, or a year after it was done.

The second group is status: total time on the airframe and on each engine and propeller, the status of life-limited parts, time since overhaul, current inspection status, the list of applicable ADs with how each was complied with, and the forms for major alterations. These records transfer with the aircraft when it is sold.

In practice, owners keep everything. Buyers, appraisers and lenders expect the full history back to the aircraft’s manufacture, and a gap in the records costs money at sale. Back-to-birth records covers where that expectation comes from and how to handle gaps.

One more rule shapes every page. Under 14 CFR 91.407, an aircraft that has had maintenance cannot fly until an authorized person approves it for return to service and the logbook entry has been made. Writing the entry is part of finishing the job.

What’s in a set of aircraft records

The records for a small piston airplane can fit in three thin books: airframe, engine and propeller. A business jet’s records fill a shelf, and they are organized around one idea: records follow serial numbers.

Engines, the APU and many components come off the aircraft for overhaul or exchange and end up on other aircraft. Each keeps its own logbook or history card, and the record moves with the part. The airframe logbook records only the removal and the installation.

Two things follow for anyone reviewing a set. The aircraft’s total time and an engine’s total time are often different numbers, and both can be right. And a component’s history can begin years before it was installed on this aircraft, so part of its record may come from other operators.

How to read a logbook entry

Many entries today, especially from repair stations, are printed on a sticker, pasted into the logbook and signed. Older entries are handwritten. The required content is the same.

For maintenance, 14 CFR 43.9 requires four things: a description of the work or a reference to data that describes it, the date the work was completed, the name of the person who did it if someone else approved it, and the approver’s signature, certificate number and kind of certificate. Inspection entries follow 14 CFR 43.11, which adds the type and extent of the inspection, the aircraft’s total time, and a return-to-service statement. The signature approves return to service only for the work described in that entry.

Step through the entry below. Each highlight is one thing a reviewer looks for.

Entries lean on shorthand. These are the abbreviations you will see most:

Numbers like 32-40-00 come from the ATA chapter system that most manuals share. Chapter 32 is landing gear, 49 is the APU, chapters 71 through 80 cover the engine, and 05 holds time limits and inspection programs. Once you know a few chapters, you can scan a page of entries and see which systems were worked on.

Hours, cycles and the calendar

Entries record the aircraft’s clocks at the time of the work. There are three, and different items run on each.

• Time in service runs from the moment the aircraft leaves the ground until it touches down at the next landing (14 CFR 1.1). It is shorter than the flight time in a pilot’s logbook, which also counts taxi.
• Cycles count landings for the airframe. Engines count cycles as their manufacturer defines them, usually one per flight. Each flight pressurizes the fuselage once, and each start and shutdown heats and spins up the disks inside a turbine engine, so most of their limits are written in cycles.
• The calendar covers what ages on the ground: inspections due every so many months, transponder and altimeter checks every 24 calendar months, and parts with shelf lives.

Many limits use two clocks at once: 300 hours or 12 months, whichever comes first. Fly the example aircraft forward and watch the order in which items come due.

Work orders: the detail behind the entry

When an aircraft goes into a shop, the shop opens a work order: a numbered job file for that visit. The requested work becomes task cards, which technicians sign as they finish each step and inspectors sign again where the shop requires a second check. Anything found along the way gets a non-routine card with the finding and the fix. Parts arrive from stores with their release paperwork.

At the end, the shop writes the logbook entry. A phase inspection can produce a work order hundreds of pages long and a logbook entry of a dozen lines, so the entry refers to the work order instead of repeating it.

That reference matters. Section 43.9 lets an entry describe the work by referring to other data, and the FAA’s records guidance, AC 43-9D, says referenced documents such as work orders are to be made part of the maintenance records and kept. The shop has to keep its own copy for only two years, and it must give the owner a copy of the maintenance release (14 CFR 145.219). After those two years, the owner’s copy of the work order may be the only one left. Keep work order packages with the logbooks.

8130-3 tags: release paperwork for parts

Parts travel with paperwork too. In the US the best-known piece is FAA Form 8130-3, the Authorized Release Certificate, which the industry calls an 8130 or a tag. It certifies one of two things about the parts listed on it.

A manufacturer uses block 13 to certify that a new part conforms to its approved design and is in a condition for safe operation. A repair station uses block 14 to certify that it did the work described on the form under Part 43 and approves the part for return to service. Only one side is filled in, and the other is shaded out. Block 11 tells you which case you are looking at: NEW for a new part, or OVERHAULED, REPAIRED, INSPECTED, TESTED or MODIFIED for a part that has been through a shop, with block 12 describing the work and the standard used.

Europe’s equivalent is the EASA Form 1. A shop approved by both the FAA and EASA can issue a dual release: one 8130-3 that serves as both.

The form has three limits:

• The form does not authorize installing the part on a particular aircraft. The form says so itself, and the installer still checks that the part is eligible for the aircraft’s configuration.
• It is not the only acceptable release. The FAA’s parts guidance, AC 20-62E, also accepts a repair station tag, a work order or a maintenance record entry that carries the required information.
• A tag covers one shop visit. For a life-limited part you need its full history of cycles back to new, and the latest tag says nothing about earlier visits.

The FAA Form 8130-3 guide goes through every block.

ADs vs. service bulletins

Service bulletins come from manufacturers. An airframe, engine or component maker publishes one when it wants operators to inspect, modify or replace something. For an aircraft operated under Part 91, the FAA treats a service bulletin as advisory: compliance is not required unless an Airworthiness Directive includes it. That holds even when the manufacturer prints MANDATORY across the top. The label tells you how seriously the manufacturer takes the problem.

Airworthiness Directives come from the FAA. Part 39 calls them legally enforceable rules, and operating a product that does not meet an applicable AD is a violation. An AD applies to every product in its applicability statement, including one that has been modified in the affected area.

The two often travel together. When the FAA decides that a problem a manufacturer has found is an unsafe condition, it can write an AD that requires the actions in the service bulletin. The bulletin then becomes part of the AD, and where the two disagree, the AD controls (14 CFR 39.27). Most ADs start as a proposed rule open for public comment. Urgent ones are issued as final rules without prior notice, and emergency ADs are sent straight to registered owners.

Two kinds of requirements apply without any AD. Replacement times and inspections in a manufacturer’s airworthiness limitations section are mandatory (14 CFR 91.403(c)). And a multiengine jet does not get an annual inspection: 14 CFR 91.409(e) requires it to follow an inspection program the operator selects, most often the manufacturer’s, so the tasks in that program become the aircraft’s inspection requirements.

Contracts can add more. An engine maintenance program, a lease or a loan agreement can require specific bulletins, which is one reason buyers ask about service bulletin status even where the law does not.

For recurring ADs, check the next-due math yourself. Recurring ADs walks through how.

A first pass through a set of logbooks

When a set of records lands on your desk, work through it in this order:

1. Read the status records first. Current times, inspection status, the AD list and life-limited parts tell you what the rest of the set has to prove.
2. Check that time only moves forward. Total time and landings should rise from entry to entry. A drop or a gap needs an explanation.
3. Follow each big event to its paperwork. For every inspection, engine change and repair, find the entry, the work order and the part tags.
4. Match serial numbers. The part’s data plate, its tag and the entry that installed it should agree.
5. Walk the AD list. For each AD, confirm it applies, check the recorded method of compliance, and recompute the next due for anything that recurs.
6. Find the paperwork behind every modification. Each alteration should have its Form 337 or STC.
7. Write gaps down as questions. A missing record is a question for the seller or the shop until someone answers it.

The pre-buy records review guide turns this into a full checklist.

Test yourself

Twelve questions, each tied to a section above. Pick an answer to see the explanation.

Sources and further reading

• 14 CFR 91.417, maintenance records
• 14 CFR 91.407, operation after maintenance
• 14 CFR 43.9, content of maintenance entries
• 14 CFR 43.11, content of inspection entries
• 14 CFR Part 39, Airworthiness Directives
• 14 CFR 91.409, inspections
• 14 CFR 145.219, repair station recordkeeping
• FAA AC 43-9D, Maintenance Records and FAA Form 8130-3 Return to Service
• FAA Form 8130-3
• FAA AC 20-62E, eligibility and identification of replacement parts
• FAA AC 20-176A, service bulletins related to Airworthiness Directives
• FAA: Service Bulletins and the Aircraft Owner
• FAA: Airworthiness Directives