Direct Answer — What §135.65 Requires
14 CFR §135.65 requires every Part 135 operator to carry an aircraft maintenance log on board each aircraft for recording or deferring mechanical irregularities and their correction. The pilot in command must enter each mechanical irregularity that comes to their attention during flight time, and before each flight must determine the status of irregularities left open at the end of the preceding flight. Whoever takes corrective action or defers the item must record that action in the log under the applicable maintenance requirements — and the operator must keep copies of the log in the aircraft per a procedure written into its §135.21 manual.
- (a)Provide the on-board log. The certificate holder provides an aircraft maintenance log carried on board for recording or deferring mechanical irregularities and their correction.
- (b)PIC records and checks. The pilot in command enters each in-flight mechanical irregularity, and before each flight determines the status of items entered at the end of the preceding flight.
- (c)Record the action. Each person who takes corrective action or defers action on a failure or malfunction records the action taken in the log under the applicable maintenance requirements of the chapter.
- (d)Keep copies on board. The operator establishes a procedure for keeping copies of the log in the aircraft for access by appropriate personnel, included in the §135.21 manual.
Source: 14 CFR §135.65 — eCFR. The authority to defer (fly with an item inoperative) comes from the operator's approved MEL under §135.179, not from §135.65 — §135.65 is the recording rule.
The on-board aircraft maintenance log — the discrepancy log, or squawk sheet — is the smallest and most-handled record in a Part 135 operation, and one of the most frequently cited in FAA surveillance reviews. Open squawks with no recorded disposition, deferrals with no MEL reference, and verbal handoffs that never made it into the log are the recurring findings. They are also almost entirely a documentation-discipline problem rather than a maintenance-capability problem.
FAA civil penalties for recordkeeping and operating violations under 49 U.S.C. § 46301 reach $75,000 per violation under 14 CFR §13.301 (for violations occurring on or after December 30, 2024), with a lower individual / small-business maximum. The discrepancy log sits directly inside the airworthiness chain that those penalties protect: it is where an in-flight irregularity becomes a recorded item, where the decision to correct or defer is documented, and where the next crew confirms the aircraft is legal to fly. This article walks the §135.65 loop step by step, shows how deferrals tie back to the Minimum Equipment List, contrasts §135.65 with the §135.443 airworthiness release, and places it in the broader §135.63 record set.
The §135.65 Loop — Five Duties, Step by Step
§135.65 is not a single requirement — it is a closed loop spanning four paragraphs, with obligations that fall on different people. Here is each duty, who owns it, and the mistake that breaks the loop.
Provide the on-board log
The operator must provide an aircraft maintenance log to be carried on board each aircraft for recording or deferring mechanical irregularities and their correction. This is the discrepancy log itself — the physical or electronic book that lives with the aircraft. The rule places the obligation to provide it on the certificate holder, not the crew.
Where the loop breaks
A fleet aircraft returns from lease or a maintenance event without its current discrepancy log pages, so the on-board record does not reflect the last open squawks. The log must travel with the aircraft.
PIC enters each in-flight irregularity
The pilot in command shall enter, or have entered, in the aircraft maintenance log each mechanical irregularity that comes to the pilot's attention during flight time. The trigger is awareness during flight time — the PIC writes it up; the entry is not optional and is not maintenance's job to reconstruct after the fact.
Where the loop breaks
A crew verbally hands off a squawk to the next crew or to maintenance without writing it in the log. Verbal handoff is not an entry. The next PIC has no record to check.
Next PIC checks open items before flight
Before each flight, if the pilot does not already know, the PIC shall determine the status of each irregularity entered in the maintenance log at the end of the preceding flight. The log is a pre-flight read obligation: the incoming PIC must know what the prior crew left open and whether it was corrected or deferred.
Where the loop breaks
A PIC dispatches without reviewing the open squawks from the preceding flight and departs with an item that should have been corrected or formally deferred under the MEL.
Record the corrective action or deferral
Each person who takes corrective action or defers action concerning a reported or observed failure or malfunction of an airframe, powerplant, propeller, rotor, or appliance shall record the action taken in the aircraft maintenance log under the applicable maintenance requirements of this chapter. A correction is a Part 43-compliant maintenance entry; a deferral is an MEL-referenced entry that placards the item inoperative.
Where the loop breaks
A squawk is signed off as "corrected" with no description of the work, or "deferred" with no MEL item cited and no placard installed. Both produce an open-loop discrepancy on inspection.
Keep copies on board per the manual procedure
The operator must establish a procedure for keeping copies of the aircraft maintenance log in the aircraft for access by appropriate personnel and include that procedure in the manual required by §135.21. The on-board record has to be accessible — and the how is written into your General Operations / General Maintenance Manual.
Where the loop breaks
The manual describes one discrepancy-log procedure and the aircraft uses another (e.g., the manual says electronic log, the aircraft carries a paper book with no defined retention). An FAA review reconciles manual to aircraft.
Why the PIC's pre-flight read is the hinge of the rule
§135.65(b) puts two obligations on the pilot in command in one paragraph: record what you find, and — before each flight — determine the status of what the last crew left open. The second is what makes the log a control rather than an archive. If the incoming PIC does not read the open items, a discrepancy that should have been corrected or formally deferred under the MEL can be flown unknowingly. That is why the discrepancy log has to be legible, current, and physically with the aircraft — and why §135.65(d) makes the operator write the access procedure into the manual.
How a Deferral Is Recorded — §135.65 Meets the MEL
§135.65 is unusual among recordkeeping rules in that its own text — in paragraph (a) — contemplates deferring mechanical irregularities, not just recording and correcting them. But §135.65 does not grant the authority to fly with an inoperative item. That authority comes from the operator's approved Minimum Equipment List under 14 CFR §135.179 (Inoperable instruments and equipment). The clean mental model: §135.179 is the authority to defer; §135.65 is the record of the deferral. An item may only be deferred if the MEL permits it and all the §135.179(a) conditions are met — an approved MEL exists for that aircraft, operations specifications authorize operation under it, the affected items are placarded or recorded as required, and the aircraft is operated under all conditions and limitations in the MEL.
A correction entry contains
- A description of the corrective action taken (the §135.65(c) record), satisfying the Part 43 maintenance entry content for the work performed
- The signature, certificate number, and kind of certificate of the person approving the work for return to service
- Cross-reference to the airworthiness release or maintenance log entry required by §135.443 where applicable
- A clear close-out so the next PIC can see the item is no longer open
A deferral entry contains
- Identification of the inoperative item and the specific MEL item invoked
- Any (M) maintenance procedure and (O) operations procedure the MEL requires, and confirmation it was performed
- The placard installed to identify the item as inoperative, as required under §135.179
- Who deferred the item and when — and the category / repair interval the MEL assigns
A deferral is a temporary record with a clock — not a permanent fix
Every MEL deferral carries a repair category that limits how long the item may remain inoperative. The discrepancy stays open in the §135.65 log until it is corrected and closed out with a maintenance entry. The two most common findings on inspection are a deferral with no MEL item cited (which reads as flying a known discrepancy with no authority) and a deferral whose repair interval has quietly expired with the item still inoperative. The log entry is the only place an inspector — or your next PIC — can see both facts at a glance.
Want to know whether your discrepancy-log close-outs and MEL deferrals would survive an FSDO review?
Discrepancy Log Entry — Compliant vs Defective
The same squawk (a landing/taxi light inoperative, discovered in flight) rendered as a clean closed loop and as a defective open loop.
Compliant — Loop Closed
[Discrepancy / who] Left landing light inoperative, noted in cruise. Entered by PIC J. Reyes, ATP 3456789. Date/time logged.
[Disposition] Deferred per MEL item 33-XX, Category C. (M) procedure n/a; (O) procedure: night ops limitation observed. INOP placard installed.
[Deferred by] DOM K. Allen, A&P 2233445 — date logged.
[Close-out] Light replaced per AMM 33-40; return-to-service entry made per §135.443. Squawk closed; placard removed.
- In-flight irregularity entered by the PIC (§135.65(b))
- Deferral cites the specific MEL item + category (§135.179)
- INOP placard installed and recorded
- Corrective action recorded; airworthiness release per §135.443
- Loop visibly closed for the next crew
Defective — Open Loop
[Discrepancy / who] "Landing light out." No name, no certificate, no date.
[Disposition] "Deferred" — no MEL item, no category, no placard noted
[Deferred by] (blank)
[Close-out] (none — item still shows open three flights later)
- Entry not attributable — no PIC name/certificate/date
- "Deferred" with no MEL item cited — reads as no authority to defer
- No INOP placard recorded (§135.179 condition unmet)
- No corrective-action / return-to-service record
- Open loop: next PIC cannot determine status (§135.65(b))
An open loop is harder to defend than a clean correction
The defective entry tells an inspector three things at once: an irregularity existed, the operator knew about it, and it was neither properly deferred nor closed. That is a worse posture than a discrepancy that was simply corrected and signed off, because the record itself demonstrates the loop was left open. The fix is structural — a log discipline where every squawk has an owner, a disposition (correct or defer-with-MEL-item), and a close-out before the item ages or the aircraft flies again.
§135.65 vs §135.443 — Two Different Records, Two Different Moments
Operators often blur the on-board discrepancy log with the airworthiness release. They are distinct records governing distinct moments in the airworthiness chain. 14 CFR §135.443 (Airworthiness release or aircraft maintenance log entry) provides that no certificate holder may operate an aircraft after maintenance, preventive maintenance, or alterations are performed unless the certificate holder prepares — or causes the person with whom it arranges to perform the work to prepare — an airworthiness release or an appropriate entry in the aircraft maintenance log, signed by an authorized person under Part 43, certifying that the work was performed in accordance with the operator's manual, that all required inspections were performed by an authorized person, and that no known condition exists that would make the aircraft unairworthy.
| Dimension | §135.65 — Discrepancy Log | §135.443 — Airworthiness Release |
|---|---|---|
| What it captures | Mechanical irregularities found in flight; their deferral or correction | Certification that maintenance returned the aircraft to service airworthy |
| Primary author | Pilot in command (the entry); maintenance (the disposition) | Person authorized under Part 43 to approve return to service |
| Trigger | An irregularity coming to the PIC’s attention during flight time | After maintenance, preventive maintenance, or alterations are performed |
| Lives where | On board the aircraft (the §135.65(a) log) | Airworthiness release or entry in the aircraft maintenance log |
| Gates what | Whether the next crew knows the aircraft’s open-item status | Whether the aircraft may be operated after the work |
In practice the two records connect at the close-out: a squawk is recorded in the §135.65 log, maintenance corrects it, and the §135.443 airworthiness release (or maintenance log entry) is what certifies the aircraft is back in service airworthy. The discrepancy log close-out should cross-reference that release. A correction noted in the discrepancy log with no corresponding §135.443 entry — or a §135.443 release that does not trace back to the originating squawk — is an audit gap on both sides. For the maintenance-record content that the corrective entry itself must satisfy, see our explainers on §43.9 maintenance record entries and Part 135 CAMP recordkeeping.
A note on aircraft size and the maintenance framework
§135.65 applies to every Part 135 aircraft. The maintenance framework around it scales with seating configuration: §135.411(a)(1) aircraft type-certificated for nine or fewer passenger seats are maintained under Parts 91 and 43 (and may use an approved aircraft inspection program under §135.419), while §135.411(a)(2) aircraft with ten or more passenger seats are maintained under a Continuous Airworthiness Maintenance Program. The §135.443 airworthiness release and the §135.439 maintenance recording requirements live in the larger-aircraft / CAMP framework; the on-board §135.65 discrepancy log obligation applies regardless. See §91.409 inspection programs for the smaller-aircraft path.
See your open squawks and expiring deferrals before an inspector does
FileFlo classifies aviation compliance documents against the governing CFR — discrepancy-log close-outs, §135.443 airworthiness releases, MEL deferral references, and the §135.63 record set — indexes them, tracks expirations, and generates an inspector-format audit binder on demand. See the full Aviation compliance coverage. FileFlo is the document and proof layer — it does not run your operation, hold your certificate, perform maintenance, or replace your MEL or safety program.
Where the Discrepancy Log Sits in the §135.63 Record Set
The on-board maintenance log does not exist in isolation. It is one record inside the broader recordkeeping obligation of 14 CFR §135.63 (Recordkeeping requirements). §135.63(a) requires the certificate holder to keep at its principal business office (or other approved location) and make available for inspection records that include the operating certificate (§135.63(a)(1)), the operations specifications (§135.63(a)(2)), a current list of the aircraft used or available for use and the operations for which each is equipped (§135.63(a)(3)), and an individual record for each pilot (§135.63(a)(4)). Separately, §135.63(d) requires the pilot in command of an aircraft for which a load manifest must be prepared to carry a copy of the completed load manifest in the aircraft to its destination, and the operator to keep copies of completed load manifests for at least 30 days.
The on-board document set
The §135.65 aircraft maintenance log travels with the aircraft alongside the other documents that must be aboard — the airworthiness and registration certificates, the ARROW document set, the load manifest under §135.63(d) where required, and the MEL information the crew must have direct access to under §135.179. The discrepancy log is the most dynamic of these — it changes every flight.
The permanent maintenance records it feeds
A correction recorded in the §135.65 log flows into the operator's permanent maintenance records. For CAMP operators, those are kept under the §135.439 maintenance recording requirements using the recordkeeping system described in the maintenance manual (§135.427), and they track total time in service, life-limited parts status, time since overhaul, current inspection status, and airworthiness directive compliance. The discrepancy log is the front door; these are the file room.
The external reports it can trigger
Some irregularities recorded under §135.65 also meet the criteria for an external report. A Service Difficulty Report under §135.415 is required to the FAA for certain failures, malfunctions, and defects; a reportable event under NTSB Part 830 is a separate notification regime. A §135.65 log entry never substitutes for these — they are distinct obligations the same event can trigger in parallel.
Related Part 135 records resources
- What Records Must a Part 135 Operator Keep — the §135.63 record set
- MEL & CDL Records — the authority to defer under §135.179
- Part 135 Service Difficulty Reports (SDR) — §135.415 reporting
- Required Inspection Items (RII) Program Records
- Part 135 CAMP Maintenance Recordkeeping — §135.439
- Part 135 GOM/GMM Manual Requirements — §135.21 / §135.427
- §43.9 Maintenance Record Entry — content of the corrective entry
- How to Prepare for a Part 135 FAA Surveillance Audit
Who Owns the §135.65 Log — and Where the Risk Concentrates
§135.65 deliberately spreads its obligations across the operation. The certificate holder provides the log and writes the procedure into the manual; the pilot in command records and checks; whoever corrects or defers records the action. The compliance risk concentrates at the seams between these roles.
Pilots in command
The highest-frequency risk is the unrecorded squawk and the skipped pre-flight read. §135.65(b) is explicit that the PIC enters each in-flight irregularity and, before each flight, determines the status of items left open by the preceding flight. For single-pilot operators the same person often writes, defers, and closes — which makes a disciplined log even more important, because there is no second set of eyes catching an open loop.
Maintenance and the director of maintenance
§135.65(c) puts the recording duty on whoever takes corrective action or defers the item. The risk concentrates on deferrals with no MEL item cited, corrections signed off without a description of the work, and the missing cross-reference to the §135.443 airworthiness release. The discrepancy log is also where an aging deferral becomes visible — or stays invisible — so close-out discipline directly protects the airworthiness chain that feeds the permanent maintenance records.
The certificate holder and the manual
§135.65(a) and (d) put two obligations squarely on the operator: provide the on-board log, and write the procedure for keeping copies in the aircraft into the §135.21 manual. An FAA surveillance review reconciles the manual's stated discrepancy-log procedure against what is actually in the aircraft — a mismatch (paper vs electronic, undefined retention, no access control) is a finding even when the individual entries are clean.
Frequently Asked Questions
What does 14 CFR §135.65 require a Part 135 operator to keep on board the aircraft?
Under 14 CFR §135.65(a), each certificate holder must provide an aircraft maintenance log to be carried on board each aircraft for recording or deferring mechanical irregularities and their correction. This on-board log is the discrepancy log (sometimes called the squawk sheet or aircraft maintenance log book). It is the running record in which the pilot in command enters irregularities found during flight time, in which deferrals are noted, and in which the corrective action is later recorded. It is separate from — but feeds — the operator's permanent maintenance records kept under §135.439.
Who is responsible for entering a mechanical irregularity in the log under §135.65?
Per §135.65(b), the pilot in command shall enter, or have entered, in the aircraft maintenance log each mechanical irregularity that comes to the pilot's attention during flight time. The PIC carries the entry obligation for in-flight discoveries — it cannot be deferred to maintenance to backfill later. The same paragraph requires that before each flight the PIC, if the pilot does not already know, determine the status of each irregularity entered in the maintenance log at the end of the preceding flight. So the log is both a write obligation (record what you find) and a read obligation (check what the last crew left open before you fly).
How is a deferral recorded under §135.65, and how does it relate to the MEL?
§135.65(a) expressly contemplates both recording and deferring mechanical irregularities in the on-board log, and §135.65(c) requires that each person who takes corrective action or defers action concerning a reported or observed failure or malfunction record the action taken in the log under the applicable maintenance requirements of this chapter. The authority to defer a discrepancy — to fly with an item inoperative — comes from the operator's approved Minimum Equipment List under §135.179, not from §135.65 itself. §135.65 is the recording rule; §135.179 is the authority-to-defer rule. A proper deferral entry identifies the item, cites the applicable MEL item and any (M) maintenance or (O) operations procedure performed, placards the item as inoperative, and records who deferred it and when.
Does §135.65 require recording when no corrective action is necessary?
The text of §135.65(c) addresses the person who takes corrective action or defers action concerning a reported or observed failure or malfunction — it requires that person to record the action taken in the log under the applicable maintenance requirements of this chapter. The clean compliance practice, and what FAA inspectors expect to see, is that every irregularity the PIC writes up gets a documented disposition in the same log: corrected (with a Part 43-compliant maintenance entry), or deferred (with an MEL reference). An open squawk with no recorded disposition before the next flight is the classic finding. We describe the no-action-required case cautiously: confirm your General Maintenance Manual procedure for signing off items that are investigated and found to require no action, because that procedure is operator-specific and approved through your manual under §135.21.
What is the difference between §135.65 and §135.443?
They cover two different moments. §135.65 governs the on-board aircraft maintenance log — the discrepancy log where the pilot in command records irregularities found during flight time and where corrective action or a deferral is noted. §135.443 governs the airworthiness release or aircraft maintenance log entry that a certificate holder must prepare before operating an aircraft after maintenance, preventive maintenance, or alterations are performed; it must be prepared by a person authorized under Part 43 and certify that the work was done in accordance with the operator's manual, that all required inspections were performed, and that no known condition exists that would make the aircraft unairworthy. In short: §135.65 captures the squawk; §135.443 documents that the fix returned the aircraft to service airworthy.
Where must copies of the §135.65 aircraft maintenance log be kept, and is that in the manual?
Per §135.65(d), each certificate holder shall establish a procedure for keeping copies of the aircraft maintenance log required by this section in the aircraft for access by appropriate personnel, and shall include that procedure in the manual required by §135.21. So §135.65 itself points back to your General Operations Manual / General Maintenance Manual: the procedure for how the discrepancy log is maintained, how copies travel with the aircraft, and who has access must be written into the manual. An FAA surveillance review frequently cross-checks the manual procedure against what is actually in the aircraft.
How does §135.65 relate to Service Difficulty Reports (SDRs)?
They are distinct obligations. §135.65 is an internal recording rule — the discrepancy goes in the aircraft maintenance log carried on board. A Service Difficulty Report is an external report to the FAA required by §135.415 (mechanical reliability reports) for certain failures, malfunctions, and defects. A single mechanical irregularity can trigger both: the PIC records it in the §135.65 log, maintenance dispositions it, and if it meets the §135.415 reporting criteria the operator also files an SDR with the FAA within the required time. See our Part 135 Service Difficulty Reports explainer for the reportable-event list and timelines; do not assume a §135.65 log entry satisfies the separate SDR obligation.
Does a single-pilot or small Part 135 operator still need the §135.65 discrepancy log?
Yes. §135.65 applies to certificate holders operating under Part 135 and is not limited by aircraft size or by whether the operation is single-pilot. Every aircraft must carry the maintenance log for recording or deferring mechanical irregularities. What changes with size is the surrounding maintenance framework: aircraft type-certificated for nine or fewer passenger seats are generally maintained under Parts 91 and 43 (per §135.411(a)(1)), while aircraft with ten or more passenger seats are maintained under a Continuous Airworthiness Maintenance Program (§135.411(a)(2)). The on-board discrepancy log requirement of §135.65 applies across both.
Related Aviation Compliance Reading
Part 135 CAMP Maintenance Recordkeeping
§135.439 records + the recordkeeping system in the §135.427 manual
MEL & CDL Minimum Equipment List Records
§135.179 authority to defer + placarding + repair categories
Part 135 Service Difficulty Reports (SDR)
§135.415 mechanical reliability reports to the FAA
§43.9 Maintenance Record Entry Requirements
Content of the corrective entry that closes a squawk
Airworthiness Directive Compliance Records
Current AD status in the permanent maintenance records
Prepare for a Part 135 FAA Surveillance Audit
How inspectors reconcile the on-board log to the manual
Keep every squawk, deferral, and close-out audit-ready
FileFlo is a compliance document intelligence platform that classifies aviation records against the governing CFR — discrepancy-log close-outs, §135.443 airworthiness releases, MEL deferral references, and the §135.63 record set — tracks expirations and aging deferrals, and generates inspector-format audit binders on demand. It is the document and proof layer; it does not run your operation, hold your certificate, perform maintenance, or replace your MEL or safety program. Starter $89/month · Professional $299/month · 5-day free trial, no credit card required.
Author: Chad Griffith, Founder, FileFlo — compliance document intelligence. This article is a compliance-document perspective on 14 CFR §135.65 and related rules; it is not legal advice or an airworthiness determination. Regulatory text is paraphrased from the cited sections and should be verified against the current eCFR and your approved manual, operations specifications, and MEL before you rely on it operationally.