There is a sentence that gets said in a lot of Part 135 maintenance meetings, and it is dangerously close to wrong: "The repair station owns that — they signed it off." The repair station owns the task. It does not own your airworthiness responsibility, and it does not own your records. When the FAA opens a records review and finds a gap, the certificate holder is the name on the enforcement action — not the shop down the ramp.
The good news is that the regulation is unusually clear about this. 14 CFR §135.437 permits outsourcing in one sentence; §135.413 keeps the airworthiness responsibility with the certificate holder in the next; §43.3 and §43.7 say who may perform and approve the work; and §135.439 plus §145.219 split the recordkeeping between the operator and the repair station.
This guide is the contracted-maintenance companion to our two maintenance deep dives — Part 135 Maintenance Recordkeeping (CAMP vs AAIP) and the cross-vertical master index in What Records Must a Part 135 Operator Keep. If your aircraft sit on the Part 91/43 baseline rather than a full program, also see Part 91 Aircraft Records Requirements.
The Rule That Lets You Outsource — 14 CFR §135.437
Start with the authority. 14 CFR §135.437 is titled "Authority to perform and approve maintenance, preventive maintenance, and alterations." Paragraph (a) is the permission slip for contracting maintenance out.
§135.437(a), in the CFR's own words
"A certificate holder may perform or make arrangements with other persons to perform maintenance, preventive maintenance, and alterations as provided in its maintenance manual. In addition, a certificate holder may perform these functions for another certificate holder as provided in the maintenance manual of the other certificate holder."
Two things to notice. First, the permission is real and broad — you may "make arrangements with other persons" for any of the three categories of work. Second, it is conditioned on one phrase that does a great deal of work: "as provided in its maintenance manual." The arrangement only counts if your manual provides for it. Outsourcing that is not reflected in your manual is not authorized outsourcing — it is a finding.
§135.437(b) adds that a certificate holder may approve a component for return to service after maintenance performed under paragraph (a) — with the important limit that, for a major repair or alteration, the work must have been done in accordance with technical data approved by the Administrator. That return-to-service authority is a separate question from who keeps the records, and we will keep the two cleanly apart throughout this guide.
"As provided in its maintenance manual" is the hinge
The single most common contracted-maintenance defect is not bad work — it is an arrangement the manual never described. The permission in §135.437(a) and the documentation requirement in §135.427(a) are two halves of the same obligation: you can outsource, but the outsourcing has to live in the manual, with the contractor listed and the work described. We unpack §135.427(a) in the arrangement section below.
Who Stays Responsible — 14 CFR §135.413
§135.437 gives you the authority to contract maintenance out. §135.413 makes sure you cannot contract responsibility out. Read together, they are the whole thesis of this guide: the work is delegable; the airworthiness responsibility is not.
§135.413(a) — the non-delegable duty
"Each certificate holder is primarily responsible for the airworthiness of its aircraft, including airframes, aircraft engines, propellers, rotors, appliances, and parts, and shall have its aircraft maintained under this chapter, and shall have defects repaired between required maintenance under part 43 of this chapter."
For aircraft maintained under the 10-or-more-seat program in §135.411(a)(2), §135.413(b) then spells out the two ways a certificate holder may discharge that duty: do the work itself under its manual, or arrange for another person to do it. The second option carries an explicit string attached.
§135.413(b)(2) — arranging the work, keeping the duty
The certificate holder may "make arrangements with another person for the performance of maintenance, preventive maintenance, or alteration. However, the certificate holder shall ensure that any maintenance, preventive maintenance, or alteration that is performed by another person is performed under the certificate holder's manual and this chapter."
That word — ensure — is the operator's ongoing obligation. It is not enough to pick a competent shop and walk away. The certificate holder must ensure the contracted work is performed under its manual and the chapter. That means the operator's program, methods, inspection standards, and required-inspection designations follow the work to the contractor's bench — and the operator has to be able to show, with records, that they did.
The CASS does not transfer either
For 10-or-more-seat operators, the §135.431 Continuing Analysis and Surveillance System applies to the inspection and maintenance programs "regardless of whether those programs are carried out by the certificate holder or by another person." So when you contract heavy maintenance to a Part 145 repair station, you still owe the continuing analysis and surveillance of that vendor's work — and the CASS audit findings, trend data, and corrective actions are part of your file. We cover the full program in Part 135 Maintenance Recordkeeping (CAMP).
Who May Perform the Work — and Who May Approve It
Outsourcing only works if the person you hand the wrench to is actually authorized to perform and approve the task. Two Part 43 sections govern this, and they answer two different questions: §43.3 — who may perform the work; and §43.7 — who may approve it for return to service.
§43.3 — Who may perform maintenance
The general rule in §43.3(a) is that "except as provided in this section and §43.17, no person may maintain, rebuild, alter, or perform preventive maintenance" on a covered article. The exceptions that matter for contracted Part 135 work: under §43.3(d), a person working under the supervision of a holder of a mechanic or repairman certificate may perform the maintenance the supervisor is authorized to perform — but only "if the supervisor personally observes the work being done to the extent necessary to ensure that it is being done properly and if the supervisor is readily available, in person, for consultation." And under §43.3(e), "the holder of a repair station certificate may perform maintenance, preventive maintenance, and alterations as provided in Part 145 of this chapter."
§43.7 — Who may approve for return to service
Performing the work and approving the return to service are different acts. §43.7 sets out the authorized approvers: under §43.7(b), "the holder of a mechanic certificate or an inspection authorization may approve an aircraft, airframe, aircraft engine, propeller, appliance, or component part for return to service as provided in Part 65"; under §43.7(c), "the holder of a repair station certificate may approve" return to service "as provided in Part 145." So a contracted repair station signs its return to service under its own certificate, within the limits of its ratings.
For the operation of the aircraft, §135.443 is the gate
Part 43 says who may approve the article. But for a 10-or-more-seat program, the aircraft cannot be operated after maintenance until the §135.443 airworthiness release is in place. Under §135.443(b)(3), that release or maintenance-log entry must be signed by an authorized certificated mechanic or repairman, and a repairman may sign only for the work for which that person is employed and certificated. The contractor's Part 145 maintenance release and the operator's §135.443 documentation are two records that must agree — we return to this in the records section.
The Arrangement — What the Manual Must Show
The regulation does not give you a contract template. What it gives you is a documentation requirement that, in effect, defines the arrangement. The arrangement lives in the operator's manual, and §135.427(a) is explicit about what has to be in it.
§135.427(a) — list the people you have arranged with
"Each certificate holder shall put in its manual the chart or description of the certificate holder's organization required by §135.423 and a list of persons with whom it has arranged for the performance of any of its required inspections, other maintenance, preventive maintenance, or alterations, including a general description of that work."
Read that against §135.437(a) ("as provided in its maintenance manual") and §135.413(b)(2) ("performed under the certificate holder's manual") and the picture is consistent: a compliant outsourcing arrangement is one your manual names, scopes, and binds to your program. Three documentation elements fall out of this:
A named contractor in the manual
The §135.427(a) list of persons with whom you have arranged for required inspections, other maintenance, preventive maintenance, or alterations — kept current as vendors change.
A general description of the work
Section 135.427(a) requires the manual to include "a general description of that work" for each listed person — what scope each contractor is arranged to perform.
A binding to your program
Per §135.413(b)(2), the arrangement must ensure the work is "performed under the certificate holder's manual and this chapter" — your methods, inspection standards, and required-inspection items, not just the shop's own procedures.
The contractor must have an "adequate organization" — §135.423
The arrangement is not just a name on a list. §135.423(a) requires that each certificate holder performing maintenance "and each person with whom it arranges for the performance of that work, must have an organization adequate to perform the work." The same standard applies to required inspections under §135.423(b). And §135.423(c) requires that where required inspections and other maintenance are performed in the same organization, those functions be separated below the level of administrative control at which overall responsibility is exercised. In other words, the FAA reaches the contractor's organizational adequacy through your arrangement — another reason the buck stays with you.
The Records — §135.439 (Yours) and §145.219 (Theirs)
Here is where operators most often go wrong: they assume that because the contractor keeps records, they do not have to. Both parties keep records, and they are different record sets serving different rules. The operator's obligation under §135.439 does not shrink because the work was contracted out.
For 10-or-more-seat aircraft, the certificate holder keeps two categories of records under §135.439:
- §135.439(a)(1) — all the records necessary to show the §135.443 airworthiness-release requirements were met.
- §135.439(a)(2) — the status records: total time in service, life-limited part status, time since overhaul, current inspection status, AD status, and the list of major alterations and repairs.
A Part 145 repair station keeps its own records under §145.219:
- §145.219(a) — retain records, in English, that demonstrate compliance with Part 43.
- §145.219(b) — provide a copy of the maintenance release to the owner or operator.
- §145.219(c) — retain those records for at least 2 years from the date the article was approved for return to service.
The §145.219(b) duty to hand the operator a copy of the maintenance release is the bridge between the two files. That copy is precisely the kind of document that becomes part of your §135.439(a)(1) release-support records. The contractor's two-year retention floor under §145.219(c) is a backstop, not your retention period — your §135.439 retention obligations are independent and, for the status records, run with the aircraft.
| Record | Who Keeps It | Retention | Authority |
|---|---|---|---|
| Release-support records | Operator | Until repeated or superseded, or 1 year after the work is performed | §135.439(a)(1), (b)(1) |
| Last complete overhaul records | Operator | Until superseded by work of equivalent scope and detail | §135.439(b)(2) |
| Status records (time, life-limit, AD, inspection, alterations) | Operator | Retained and transferred with the aircraft on sale | §135.439(a)(2), (b)(3) |
| Repair station records demonstrating Part 43 compliance | Contractor (Part 145) | At least 2 years from return-to-service date | §145.219(a), (c) |
| Copy of maintenance release | Contractor → Operator | Provided to owner/operator; folds into operator (a)(1) records | §145.219(b) |
The contractor's entry still has to satisfy §43.9 or §43.11
Whoever performs the work, the maintenance-record entry must satisfy the Part 43 content rules. §43.9 governs entries for maintenance, preventive maintenance, rebuilding, and alterations — requiring a description of the work, the date of completion, the name of the person performing the work if different from the approver, and the signature, certificate number, and kind of certificate of the person approving the work. Inspections are different: §43.9(c) excludes the inspections under parts 91 and 125 and §§135.411(a)(1) and 135.419 from §43.9, and §43.11 is the section that prescribes inspection-record content. Our §43.9 maintenance-entry guide breaks the required elements down — and a contractor's entry missing the certificate number or kind of certificate is a records defect that lands on your file.
Two Files, One Truth — Reconciling the Contractor's Records With Yours
The reason contracted maintenance generates findings is rarely that the work was bad. It is that the operator's file and the contractor's file tell slightly different stories — a release the operator never pulled, an AD next-due the contractor updated but the operator's status record did not, a part-traceability document that lives only in the shop's system. The fix is a reconciliation discipline: every time work comes back, the operator's §135.439 records are updated from the contractor's output.
The contracted-work close-out checklist
Pull the maintenance release
Obtain the §145.219(b) copy of the maintenance release and any supporting documents from the contractor — do not leave them only in the shop file.
Confirm the §135.443 release
Verify the airworthiness release / log entry is signed by an authorized certificated mechanic or repairman before the aircraft is operated (§135.443(b)(3)).
Update the status records
Roll any change to AD status, inspection status, time since overhaul, or life-limited parts into the §135.439(a)(2) records — the aircraft's living status set.
Check the §43.9 / §43.11 entry
Confirm the entry has the description, date, name, and signature/certificate-number/kind-of-certificate that Part 43 requires.
Feed the CASS
For a 10-or-more-seat program, log the work in the §135.431 continuing-analysis loop — including surveillance of the vendor.
Confirm the manual still names the vendor
Verify the contractor and the work scope are reflected in the §135.427(a) list, and that the arrangement is current.
For the AD piece specifically — the status record contracted work most often disturbs — see How to Document AD Compliance So It Survives a Ramp Check. For what an inspector actually asks the repair station for, see The Part 145 Audit Binder and Part 145 Repair Station Recordkeeping. And when the work touches a major repair or alteration, the FAA Form 337 guide covers the documentation §135.437(b) ties to approved technical data, while life-limited parts records and engine and propeller overhaul tracking cover two status records that shops routinely advance.
Why the exposure sits with you
Because the operator owns the §135.439 records and the §135.413(a) airworthiness responsibility, a records deficiency on contracted work is charged against the certificate holder. Under 14 CFR §13.301, for violations occurring on or after December 30, 2024, the maximum civil penalty under 49 U.S.C. 46301(a)(1) is $75,000 for a person other than an individual or small business concern, and $1,875 for an individual or small business concern, per violation. A thin contracted-maintenance file is not the contractor's problem to explain to your Principal Maintenance Inspector — it is yours.
The Contracted-Maintenance Records You Must Be Able to Produce
Pulling the threads together, here is the contracted-maintenance record set a Part 135 operator must hold and be able to produce on demand — each mapped to its governing section. Note that every item below is the operator's to produce, even when the contractor generated the underlying document.
The arrangement, in the manual
The §135.427(a) list of persons you have arranged with for required inspections, other maintenance, preventive maintenance, or alterations — plus a general description of each one's work.
Airworthiness releases + support records
Every §135.443 release and the §135.439(a)(1) records (work orders, inspection sign-offs, parts traceability, the §145.219(b) maintenance-release copy) that substantiate it.
Status records
The §135.439(a)(2) set — total time in service, life-limited parts, time since overhaul, current inspection status, AD status, major alterations and repairs — updated from each contractor's output.
CASS records on contracted work
The §135.431 continuing-analysis findings, vendor surveillance, trend data, and corrective actions — for work "carried out by another person."
Part 43 entries
The §43.9 maintenance entries and §43.11 inspection entries — with the description, date, name, and signature/certificate-number/kind-of-certificate the rule requires.
Return-to-service authority trail
Evidence that the approver was authorized under §43.7 and, for the §135.443 release, an authorized certificated mechanic or repairman.
For the upstream framework — the two maintenance tracks and which one your aircraft sits on — see Part 135 Maintenance Recordkeeping (CAMP vs AAIP). For how operational control intersects with who is responsible for the aircraft, see What Is Operational Control in Part 135. And to see the whole records picture an inspector walks through, start with how to prepare for a Part 135 FAA surveillance audit.
Keep every contracted-maintenance record audit-ready
FileFlo is a compliance document intelligence platform — a read-only proof layer that classifies and tracks the records your maintenance program produces, including the documents your contractors hand back. It does not run your maintenance program, your CASS, or your maintenance-tracking system, it does not sign off maintenance, and it makes no live connection to your repair station's systems. You upload the documents; FileFlo:
- Classifies each document against the governing CFR (§135.439, §135.443, §135.437, §145.219, §43.9/§43.11)
- Indexes the contractor's §145.219(b) maintenance-release copy into your §135.439(a)(1) release-support records
- Extracts dates and statuses and tracks expirations — AD next-due, inspection status, life-limited part timelines disturbed by contracted work
- Sends 90/60/30-day expiration alerts before a recurring AD or inspection lapses — not the day after
- Generates an audit-ready maintenance-records binder organized by section for an FAA surveillance visit or a pre-purchase review
FileFlo sits alongside your Director of Maintenance, your A&P/IA, and your Part 145 repair station — it keeps the documents that prove your compliance; it does not perform, supervise, or sign off maintenance. Starter $89/mo · Professional $299/mo · 5-day free trial, no credit card required.
Related Aviation Recordkeeping Guides
Frequently Asked Questions
Can a Part 135 operator outsource its maintenance to a repair station?
Yes. 14 CFR §135.437(a) expressly says a certificate holder "may perform or make arrangements with other persons to perform maintenance, preventive maintenance, and alterations as provided in its maintenance manual." For aircraft maintained under the §135.411(a)(2) program, §135.413(b)(2) lets the certificate holder "make arrangements with another person for the performance of maintenance, preventive maintenance, or alteration." So contracting out the work itself is squarely permitted. What you cannot do is contract out responsibility for the result — §135.413(a) makes each certificate holder "primarily responsible for the airworthiness of its aircraft," and §135.413(b)(2) requires the certificate holder to ensure that any work performed by another person is "performed under the certificate holder's manual and this chapter."
Who is responsible for airworthiness when maintenance is contracted out?
The certificate holder — always. 14 CFR §135.413(a) states that "each certificate holder is primarily responsible for the airworthiness of its aircraft, including airframes, aircraft engines, propellers, rotors, appliances, and parts, and shall have its aircraft maintained under this chapter, and shall have defects repaired between required maintenance under part 43 of this chapter." That responsibility does not move to the repair station or contract mechanic when you hand them the work. The contractor is responsible for performing and properly approving the specific task under its own certificate (a Part 145 repair station under Part 145; a mechanic or IA under Part 65), but the operator remains the party the FAA holds accountable for the airframe being airworthy and for the records that prove it.
Does the contractor or the operator keep the Part 135 maintenance records?
Both keep records, but they are different record sets and the operator can never rely on the contractor's file as a substitute for its own. Under 14 CFR §135.439, the certificate holder must keep its own maintenance records — the records that show the §135.443 airworthiness-release requirements were met (§135.439(a)(1)) and the aircraft status records: total time in service, life-limited part status, time since overhaul, current inspection status, applicable airworthiness directive status, and the list of major alterations and repairs (§135.439(a)(2)). Separately, a Part 145 repair station must, under §145.219(b), "provide a copy of the maintenance release to the owner or operator," and must under §145.219(c) "retain the records required by this section for at least 2 years from the date the article was approved for return to service." The operator pulls the contractor's release and supporting documents into its own §135.439 records — it does not leave them sitting only in the shop's files.
What must a Part 135 maintenance contract or arrangement actually contain?
The regulation does not prescribe a contract template, but it imposes a documentation requirement that effectively defines the arrangement. 14 CFR §135.427(a) requires the certificate holder to put in its manual "a list of persons with whom it has arranged for the performance of any of its required inspections, other maintenance, preventive maintenance, or alterations, including a general description of that work." And §135.413(b)(2) requires the certificate holder to ensure the contracted work is "performed under the certificate holder's manual and this chapter" — which means the arrangement has to bind the contractor to the operator's program, methods, and standards, not just to the shop's own procedures. In practice the written agreement identifies the work scope, ties it to the operator's manual and inspection program, and establishes how the contractor documents and returns the work.
Who can sign the return to service on contracted Part 135 maintenance?
For aircraft on the §135.411(a)(2) program, the §135.443 airworthiness release or aircraft-maintenance-log entry must, under §135.443(b)(3), be signed by an authorized certificated mechanic or repairman — and a repairman may sign only for the work for which that person is employed and certificated. More generally, 14 CFR §43.7 sets out who may approve an article for return to service: under §43.7(b), the holder of a mechanic certificate or an inspection authorization may approve return to service as provided in Part 65; under §43.7(c), the holder of a repair station certificate may approve return to service as provided in Part 145. So a contracted Part 145 repair station signs its maintenance release under its own certificate, and the certificate holder folds that release into the §135.443 documentation for the aircraft.
Is the operator's Continuing Analysis and Surveillance System still required for contracted work?
Yes — and this is the trap operators fall into. The §135.431 Continuing Analysis and Surveillance System (CASS) for a 10-or-more-seat program applies to the inspection and maintenance programs "regardless of whether those programs are carried out by the certificate holder or by another person." Outsourcing the wrench-turning does not outsource the surveillance. The certificate holder must still analyze the performance and effectiveness of the contracted maintenance and correct deficiencies in it — and the CASS records (audit findings on the vendor, trend data, corrective actions) are part of the operator's file, not the contractor's.
Does §43.9 or §43.11 govern the contractor's maintenance-record entry?
It depends on whether the task was maintenance or an inspection. Routine maintenance, preventive maintenance, rebuilding, and alteration entries are governed by 14 CFR §43.9, which requires a description of the work (or reference to acceptable data), the date of completion, the name of the person performing the work if other than the person approving it, and — when the work was done satisfactorily — the signature, certificate number, and kind of certificate held by the person approving the work. Inspection entries are governed by a different section: §43.9(c) excludes from §43.9 the inspections conducted under parts 91 and 125 and §§135.411(a)(1) and 135.419, and §43.11 is the section that prescribes the content of inspection records. So a contractor's entry for, say, an annual or progressive inspection follows §43.11; an entry for replacing a component follows §43.9. A release backed by an entry missing the certificate number or kind of certificate is a records defect even if the work was performed correctly.
What is the civil-penalty exposure if contracted-maintenance records are deficient?
Records deficiencies are enforced against the certificate holder because the operator owns the §135.439 records and the §135.413(a) airworthiness responsibility. Under 14 CFR §13.301, for violations occurring on or after December 30, 2024, the maximum civil penalty under 49 U.S.C. 46301(a)(1) is $75,000 for a person other than an individual or small business concern, and $1,875 for an individual or small business concern, per violation. Because a single missing or defective record can be charged as a separate violation, and because an unsubstantiated airworthiness release can call the operation of the aircraft itself into question, the practical exposure from a thin contracted-maintenance file is far larger than the per-violation figure suggests.
More Part 135 & Aviation Compliance Guides
Part 135 Maintenance Recordkeeping (CAMP vs AAIP)
The two maintenance tracks, the §135.431 CASS, and the §135.439 record categories and retention
What Records Must a Part 135 Operator Keep
The master index: every Part 135 record mapped to its CFR cite, owner, and retention period
Part 145 Repair Station Recordkeeping
What §145.219 demands of the repair stations that perform your contracted maintenance
The Part 145 Audit Binder
Every document an FAA inspector asks the repair station for during a surveillance visit
What a §43.9 Maintenance Entry Must Contain
The required elements of every compliant aviation maintenance record entry
Document AD Compliance for a Ramp Check
Logbook wording, recurring-AD next-due math, and the status record contracted work disturbs
FAA Form 337 Major Repair & Alteration Records
The approved-technical-data documentation §135.437(b) ties to major repairs and alterations
Life-Limited Parts Records Requirements
The §135.439(a)(2) life-limit status record that engine and component shops advance
Engine & Propeller Overhaul Time Tracking
Time-since-overhaul status records and the last-complete-overhaul retention rule
What Is Operational Control in Part 135
How §1.1 and §135.77 define operational control — the responsibility parallel to §135.413
Prepare for a Part 135 FAA Surveillance Audit
The documents an FAA inspector requests during a SAS surveillance visit, in order
Part 91 Aircraft Records Requirements
The §91.417 framework for nine-or-fewer-seat aircraft on the Part 91/43 track
Prove your contracted-maintenance records before the FAA asks
You can outsource the wrench. You cannot outsource the §135.413(a) responsibility or the §135.439 records. FileFlo classifies every airworthiness release, maintenance-release copy, status record, and CASS finding against the governing CFR, extracts AD and inspection due dates, and sends 90/60/30-day alerts before any recurring item lapses — so the file you hand your Principal Maintenance Inspector is complete no matter who turned the wrench.
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