An aircraft engine's logbook is far more than a paper trail — it is a legal document that establishes the engine's identity, its maintenance history, and its current airworthiness status. Every time a certificated mechanic performs an inspection, replaces a component, completes an overhaul, or approves an engine for return to service, that work must be recorded in a specific, legally prescribed way. Without complete, accurate records, an engine of unknown history cannot be legally placed in service, and the aircraft it powers cannot legally carry passengers or be used for compensation. For the Aviation Maintenance Technician (AMT) studying for the Powerplant knowledge test, understanding what must be recorded, who may make entries, and what those entries must contain is essential both for the exam and for safe, compliant maintenance practice.
The governing regulations for engine records are found primarily in 14 CFR Part 43 (Maintenance, Preventive Maintenance, Rebuilding, and Alteration) and 14 CFR Part 91 (General Operating and Flight Rules, particularly §91.417). Together these regulations define who keeps the records, what those records must contain, and how long they must be retained. The FAA's Aviation Maintenance Technician Handbook — General (FAA-H-8083-30) also provides authoritative guidance on documentation practices that every powerplant technician must internalize.
What Must Be Recorded
Under 14 CFR Part 43, §43.9, each person who performs maintenance, preventive maintenance, rebuilding, or an alteration on an aircraft engine must make a record of that work. The entry must include the following elements:
- Description of the work performed — a plain-language description sufficient to identify what was done. Vague entries such as "engine work" are insufficient. The description must be specific enough that another qualified mechanic, reading it months later, understands exactly what was accomplished.
- Date of completion — the calendar date on which the work was completed and the engine was returned to service.
- Name of the person performing the work — the full name of the individual who did the work, not just an initials or a shop name.
- Certificate number and certificate type — the FAA certificate number of the certificated mechanic or repairman who approved the work, along with the type of certificate held (e.g., Airframe and Powerplant, Repairman).
- Return to service statement — a statement that the aircraft or engine is approved for return to service, or a reference to the applicable data used, such as an Airworthiness Directive (AD) number, a Supplemental Type Certificate (STC), or a manufacturer's service bulletin.
It is critically important to note that making the logbook entry and signing the return-to-service approval are inseparable. An engine cannot be legally returned to service without both the completed work and the corresponding written record and signature. Performing outstanding work without making the required entry is a violation of federal aviation regulations.
Major Inspections and 100-Hour / Annual Entries
When an Annual Inspection or a 100-Hour Inspection is performed, the recording requirements are governed by 14 CFR Part 43, Appendix B. The person performing the inspection must make a record that identifies the aircraft and engine by make, model, and serial number, and states whether the engine was found to be airworthy or unairworthy. If the engine is approved for return to service following the inspection, the entry must include the phrase or equivalent statement that the engine was inspected in accordance with a current inspection checklist and found to be in airworthy condition. If defects were found that prevent the engine from being approved, the mechanic records those discrepancies and the owner is notified in writing — the engine remains grounded until the discrepancies are corrected and a new return-to-service approval is entered.
For a 100-Hour Inspection, a mechanic holding an Airframe and Powerplant (A&P) certificate may perform the inspection and sign the return-to-service entry. For an Annual Inspection, the entry must be signed by an Inspection Authorization (IA) holder — a mechanic who has been granted special authorization by the FAA to perform annual inspections. This distinction appears regularly on FAA knowledge tests and is a common source of confusion for students.
Engine Overhaul Records
An engine overhaul — whether a major overhaul or a top overhaul — generates some of the most critical entries in the engine logbook. The FAA distinguishes between two categories of overhauled engines: those that have been overhauled and those that have been rebuilt. The difference is significant and has direct bearing on the engine's time tracking.
An overhauled engine is one that has been disassembled, cleaned, inspected, repaired as necessary, and reassembled, tested, and approved in accordance with approved standards. After overhaul, the engine's total time in service continues to accumulate from the original manufacture date. The logbook entry must state that the engine was overhauled, reference the data used (manufacturer's overhaul manual, applicable ADs, etc.), and note the total time in service at the time of overhaul.
A rebuilt engine, however, is a much more restrictive category. Under 14 CFR §43.2, only the original manufacturer or a manufacturer's authorized agent may rebuild an engine and give it zero-time status — meaning the engine starts its service life over with zero total time on the new logbook. A certificated repair station or an individual A&P mechanic cannot rebuild an engine to zero-time status, regardless of the quality of the work. When a manufacturer rebuilds an engine and issues a new logbook, the new logbook must state that the engine has been rebuilt and may start at zero hours total time. This distinction between overhauled and rebuilt is a highly tested concept on the powerplant knowledge exam.
Airworthiness Directives and Service Document Compliance
One of the most legally significant categories of engine logbook entry involves compliance with Airworthiness Directives (ADs). ADs are regulations issued by the FAA under 14 CFR Part 39 that require specific inspections, modifications, or operational limits to correct known unsafe conditions. When an AD is complied with, the entry must state the AD number, the revision date of the AD, the method of compliance used, and the date and total time in service at compliance. For recurring ADs, the entry must also state when the next compliance is due — for example, the next inspection interval in hours or calendar time.
Failure to record AD compliance properly is not merely a paperwork offense — it can render the engine legally unairworthy even if the physical work was done correctly. Inspectors and prospective buyers rely on these entries to confirm regulatory compliance.
Key Numbers and Rules
- 14 CFR §43.9 — governs content requirements for maintenance record entries (description, date, name, certificate number, return-to-service statement).
- 14 CFR §43.11 — governs the specific content of inspection entries (Annual, 100-Hour, Progressive).
- 14 CFR §91.417(a) — requires owners and operators to keep maintenance records for the airframe, each engine, propeller, rotor, and appliance.
- 14 CFR §91.417(b) — records of total time in service, current status of life-limited parts, and the time since the last overhaul must be retained for the duration of the aircraft's service life, or transferred with the aircraft upon sale.
- Records of completed work (other than overhaul and AD compliance) may be discarded after one year under §91.417(b)(1), but time-in-service records must be retained permanently.
- Only the original manufacturer (or authorized agent) can issue a zero-time logbook for a rebuilt engine — not an independent repair station or individual mechanic.
- Annual Inspection return-to-service requires an IA signature; a 100-Hour Inspection may be signed by an A&P mechanic without an IA.
Why Accurate Records Matter
Beyond passing the exam, the importance of accurate engine records cannot be overstated from a safety perspective. The engine logbook tells the story of every critical component's service life. Life-limited parts — such as turbine discs on turbine engines — have mandatory replacement intervals that can only be reliably enforced if time-in-service records are complete and unbroken. A gap in the logbook is not simply inconvenient; it may mean a part of unknown total time is installed in the engine. If that part has exceeded its service limit, the engine is operating in an unsafe condition that no visual inspection can detect.
From a legal and economic standpoint, an engine with a complete, unbroken logbook history is worth significantly more than one with missing entries. Lenders, insurers, and buyers all scrutinize logbooks carefully. An AMT who maintains complete, legible, and accurate records protects not only the flying public but also the aircraft owner's investment and their own professional reputation and certificate.
Common Test Traps
- Rebuilt vs. Overhauled zero-time confusion: Only the original manufacturer can give an engine a zero-time logbook after rebuilding. An independent mechanic or repair station performing a major overhaul cannot reset the engine's total time to zero — the total time in service continues uninterrupted.
- Who can sign an Annual vs. 100-Hour return-to-service: An A&P mechanic (without an IA) may sign off a 100-Hour Inspection return to service but cannot sign an Annual Inspection. The IA is required for Annuals.
- The entry IS the approval: Performing the maintenance without making the logbook entry and signing the return-to-service statement is a regulatory violation. The entry is not optional documentation — it is part of the legal act of returning the engine to service.
- AD entry requirements: The AD number, revision date, method of compliance, date of compliance, and next compliance due date (for recurring ADs) must all appear in the entry. Omitting any one of these makes the AD compliance record incomplete.
- Records retention periods: Students often assume all maintenance records must be kept forever. In fact, records of routine completed maintenance work (not involving overhaul or life-limited parts) need only be retained for one year. However, records of total time in service, life-limited parts status, and overhaul must be retained for the life of the aircraft.