Most maintenance on a transport aircraft is a one-person job: a qualified mechanic does the work, signs it off, and the aircraft returns to service. But a small set of tasks are different. Rig a flight control backwards, install a control cable with the turnbuckle safety wire missing, or torque a critical engine fitting wrong, and the error may not show up until the aircraft is airborne and it is too late. For exactly those tasks, 14 CFR Part 135 requires a second set of trained eyes — and it requires that the second person be someone other than the one who did the work.
That is the Required Inspection Item program. It is built from two sections that work as a pair: §135.427 (the manual content that designates the RIIs and the people who may inspect them) and §135.429 (who may perform a required inspection, and the rule that they cannot have done the work). Underneath sits §135.423, which forces the same separation onto the organization chart.
This guide walks the whole program at the records layer. If you want the master index of every Part 135 record — pilot files, drug-and-alcohol, training, maintenance — start with What Records Must a Part 135 Operator Keep, and treat this as the RII deep dive within the 10-or-more-seat maintenance program.
What Makes an Item a Required Inspection Item
The designation is a manual function. Under 14 CFR §135.427(b)(2), each certificate holder must put in its manual a designation of the items of maintenance and alteration that must be inspected (required inspections) — and the regulation sets a floor for what has to be on that list: at least those items that could result in a failure, malfunction, or defect endangering the safe operation of the aircraft, if not performed properly or if improper parts or materials are used.
Read that floor carefully, because it does two things. It tells you the character of an RII — a task where a single undetected error or a single wrong part is potentially catastrophic — and it tells you the list is a minimum, not a ceiling. The certificate holder, working with its FAA principal maintenance inspector, can designate additional items beyond the safety-critical floor. What it cannot do is leave a catastrophic-error task off the list.
The kinds of work typically designated RII
The CFR sets the test (could-endanger-safe-operation) rather than enumerating items, so the specific RII list is the certificate holder's, approved through its program. In practice, the categories that almost always appear include:
- Flight-control system installation, rigging, and adjustment — primary and secondary controls.
- Primary structure and structural repairs whose failure would be catastrophic.
- Engine, propeller, and rotor installation, and major engine work affecting power or control.
- Major repairs and major alterations on critical systems.
- Work on systems where a single error has no independent backstop before flight.
The exact list is operator-specific and lives in the manual under §135.427(b)(2). Treat the above as the recurring pattern, not a substitute for your approved RII list.
An RII is not the same thing as the inspection that returns an aircraft to service generally. It is an extra layer for the highest-consequence work — a second, independent verification stacked on top of the normal maintenance sign-off. That extra layer is the entire reason the program exists, and it is why the separation-of-authority rule below is not a technicality.
Which Aircraft Carry an RII Program — 14 CFR §135.411(a)(2)
The RII program is part of the larger continuous-airworthiness maintenance program, and that program is keyed to one number: the aircraft's type-certificated passenger seating configuration. Under 14 CFR §135.411(a)(2), aircraft type certificated for a passenger seating configuration of 10 seats or more (excluding any pilot seat) must be maintained under a maintenance program in §§135.415, 135.417, and 135.423 through 135.443. Sections 135.427 and 135.429 — the RII sections — fall squarely inside that 135.423-through-135.443 block.
Nine seats or fewer — §135.411(a)(1): no RII program as such
Aircraft type certificated for nine seats or fewer (excluding any pilot seat) are maintained under parts 91 and 43 plus §§135.415, 135.417, 135.421, and 135.422. There is no designated required-inspection-item program in the §135.427 sense for these aircraft. Their maintenance is still inspected and returned to service — under the part 43 entry rules — but the formal RII layer, the manual designation, and the §135.429 personnel requirements do not attach.
Ten seats or more — §135.411(a)(2): full RII program
Aircraft type certificated for 10 seats or more (excluding any pilot seat) carry the complete program — the maintenance organization (§135.423), the manual with its RII designations (§135.427), the required inspection personnel rules (§135.429), and the rest of the §§135.423–135.443 block. A nine-or-fewer-seat operator may elect the §135.411(a)(2) program under §135.411(b); if it does, the RII obligations come with the election.
It is type-certificated seats, not installed seats
The threshold is measured by the type-certificated passenger seating configuration, excluding any pilot seat — not by how many seats are bolted in today. Pulling seats to fly an executive interior does not move a 10-seat type design onto the nine-or-fewer track. If you are sorting which of your aircraft carry an RII program, start from the type certificate data sheet, and see our CAMP-vs-AAIP maintenance recordkeeping guide for how the 9-vs-10 line drives the rest of the program.
The Separation-of-Authority Rule — 14 CFR §135.429(c)
This is the rule that gives the RII program its integrity, and it is short. Under §135.429(c), no person may perform a required inspection if that person performed the item of work required to be inspected. The mechanic who did the work cannot be the inspector who buys it off as a required inspection. Two different qualified people, full stop.
The rule operates at two levels
At the individual level — §135.429(c): the person who performed the item of work is disqualified from performing the required inspection of that work. This is the no-self-inspection rule, and it applies every single time an RII is performed, including on buy-backs.
At the organizational level — §135.423(c): a certificate holder performing required inspections in addition to other maintenance must organize the work so as to separate the required-inspection functions from the other maintenance functions. The regulation specifies how deep the separation goes: it must exist below the level of administrative control at which overall responsibility for the required inspection functions and other maintenance, preventive maintenance, and alterations is exercised. In other words, inspection and maintenance can ultimately roll up to one accountable executive at the top — but below that point, the two chains must be distinct.
The small-shop trap
The separation rule is hardest in a small maintenance organization where the same handful of people do everything. It is tempting, when one mechanic is on duty, to let that mechanic both perform and inspect a required item. §135.429(c) does not bend for staffing convenience. If the only qualified person on shift did the work, the required inspection has to wait for a second authorized person — or the work cannot be designated and signed as an RII inspection by that person. Building the duty roster around RII coverage is part of running the program, and the records have to show two distinct people on the work and the inspection.
This is the same structural logic you see elsewhere in compliance: the person who does the thing cannot be the sole person who verifies the thing. It is why Part 145 repair stations maintain inspection functions distinct from production, and it is the maintenance-side cousin of the operational-control accountability you can read about in What Is Operational Control in Part 135.
What the Manual Must Say — 14 CFR §135.427
The RII program is documented in the maintenance manual. Section 135.427 is titled "Manual requirements," and several of its paragraphs are specifically about required inspections. Here is each one, mapped to what it obligates.
| Paragraph | What the manual must contain |
|---|---|
| §135.427(a) | The chart or description of the organization required by §135.423, and a list of persons with whom the certificate holder has arranged for the performance of any of its required inspections, other maintenance, preventive maintenance, or alterations — including a general description of that work. |
| §135.427(b)(2) | A designation of the items of maintenance and alteration that must be inspected (required inspections) — including at least those that could result in a failure, malfunction, or defect endangering the safe operation of the aircraft. |
| §135.427(b)(3) | The method of performing required inspections and a designation by occupational title of personnel authorized to perform each required inspection. |
| §135.427(b)(4) | Procedures for the reinspection of work performed under previous required inspection findings (buy-back procedures). |
| §135.427(b)(5) | Procedures, standards, and limits necessary for required inspections and acceptance or rejection of items inspected, and for periodic inspection and calibration of precision tools, measuring devices, and test equipment. |
| §135.427(b)(6) | Procedures to ensure that all required inspections are performed. |
| §135.427(c) | A system (which may be coded) that retains a description of the work performed, the name of the person performing the work if performed by an outside person, and the name or other positive identification of the individual approving the work. |
A "buy-back" is the reinspection of work performed to correct a previous required-inspection finding. Because a buy-back is itself a required inspection, the §135.429(c) separation rule still applies: the person who corrected the rejected work cannot be the person who buys it back. Buy-back records are where the loop on a safety-critical discrepancy is closed — and a frequent focus of an FAA records review.
The same paragraph that sets RII acceptance/rejection standards also requires procedures for the periodic inspection and calibration of precision tools, measuring devices, and test equipment. Calibration certificates and their due dates are RII-program records: an out-of-cal torque wrench used on a required-inspection item undermines the inspection itself. Track the calibration due dates the way you track an inspector's authorization currency.
§135.427(c) — the work-record retention system
Beyond designating the RIIs and the people, §135.427(c) requires the certificate holder to establish a system — which may be coded — that retains a description (or reference to acceptable data) of the work performed, the name of the person performing the work if that person is outside the certificate holder's organization, and the name or other positive identification of the individual approving the work. This is the paragraph that connects the RII program to the broader §135.439 records set and the §43.9 entry content rules — positive identification of who approved the work is the thread that runs through all of them.
Who May Perform a Required Inspection — 14 CFR §135.429
Designating the items is half the program; the other half is controlling who may inspect them. Section 135.429 sets the qualification, supervision, and separation requirements for required inspection personnel.
§135.429(a) — certificated, trained, qualified, authorized
No person may use any person to perform required inspections unless the person performing the inspection is appropriately certificated, properly trained, qualified, and authorized to do so. Four distinct conditions — and all four must be satisfied. Certificated is not the same as authorized: an A&P certificate is necessary but not sufficient. The person must also be specifically authorized by the certificate holder to conduct the particular required inspection, which is what puts them on the §135.429(e) list.
§135.429(b) — under the supervision and control of an inspection unit
No person may allow any person to perform a required inspection unless, at the time, the person performing that inspection is under the supervision and control of an inspection unit. This is the organizational anchor for the separation built by §135.423(c): the inspector acts as part of an inspection unit, not the production/maintenance unit, at the moment the inspection is performed.
§135.429(c) — no self-inspection
No person may perform a required inspection if that person performed the item of work required to be inspected. The separation-of-authority rule, covered in full above. It is the single most important integrity control in the RII program, and the one whose violation is easiest to spot in the records: the work signature and the required-inspection signature must belong to two different people.
§135.429(d) — the limited remote-rotorcraft exception
Section 135.429 includes a narrow exception, in paragraph (d), for rotorcraft operated in a remote area where the certificate holder cannot satisfy the inspector-availability requirements — subject to conditions and FAA approval. It is genuinely an edge case, written for specific operations, and it does not relax the program for ordinary maintenance bases. If you think you may rely on it, confirm the exact current conditions in the rule text and with your principal maintenance inspector rather than from memory.
The training behind "qualified" — §135.433
The "properly trained" and "qualified" conditions in §135.429(a) are backed by §135.433, the maintenance and preventive maintenance training program. It requires the certificate holder, or a person performing maintenance for it, to have a training program ensuring that each person — including inspection personnel — who determines the adequacy of work done is fully informed about procedures, techniques, and new equipment in use, and is competent to perform their duties. The RII training records that prove this are part of the program's evidence base, alongside the authorized-personnel list.
The Authorized-Inspector List — Who Keeps It (14 CFR §135.429(e))
A program that controls who may inspect safety-critical work is only as good as its record of who is authorized. The CFR puts that duty squarely on the certificate holder. Under §135.429(e), each certificate holder shall maintain, or shall determine that each person with whom it arranges to perform its required inspections maintains, a current listing of persons who have been trained, qualified, and authorized to conduct required inspections.
Two ways to satisfy §135.429(e)
- Maintain it yourself. The certificate holder keeps the current listing of authorized RII personnel as its own record.
- Confirm the contractor maintains it. If you arrange for an outside organization to perform your required inspections, you must determine that that organization keeps the listing. The duty does not disappear when the work is contracted — it just shifts to verifying the contractor's records.
Either way, the word that does the work is current. The list has to reflect who is authorized now — additions when people complete training, removals when they change roles or leave. A list that names a mechanic who left two years ago, or omits one authorized last month, is a defect even if every actual inspection was performed by a properly authorized person.
The list does not stand alone. It interlocks with the manual designations in §135.427(b)(3) — the personnel authorized to perform each required inspection, designated by occupational title — and with the §135.427(a) requirement to list the outside persons with whom the certificate holder has arranged to perform any of its required inspections, other maintenance, preventive maintenance, or alterations. An FAA inspector reading the program will cross-check these against each other and against the actual inspection signatures in the records.
What a surveillance review tests
During a Part 135 surveillance review, the RII program is one of the highest-scrutiny areas because the consequence of failure is so high. Expect a principal maintenance inspector to: pull a recent RII and confirm the work signature and the inspection signature are different people (§135.429(c)); confirm the inspector was on the current authorized list at the date of inspection (§135.429(e)); trace a buy-back through correction and reinspection (§135.427(b)(4)); and check that tool-calibration records support the inspections (§135.427(b)(5)). Each of those is a documentary test — which is precisely the layer where records discipline either holds or fails.
The RII Records You Must Be Able to Produce
Pulling the program together, here is the RII record set a 10-or-more-seat Part 135 operator must keep current and be able to produce on demand — each mapped to its governing paragraph.
RII designation list (in the manual)
The §135.427(b)(2) designation of which items of maintenance and alteration are required inspections — the could-endanger-safe-operation floor plus any additional items designated.
Authorized-personnel list
The §135.429(e) current listing of persons trained, qualified, and authorized to conduct required inspections — kept by the certificate holder or confirmed kept by the contractor.
Manual designations by occupational title
The §135.427(b)(3) method-of-inspection and the occupational titles authorized to perform each required inspection, plus the §135.427(a) outside-persons list.
RII inspection sign-offs
For each performed RII, two distinct signatures — the work and the required inspection — demonstrating §135.429(c) separation, with positive ID of the approver per §135.427(c).
Buy-back records
The §135.427(b)(4) reinspection records closing out work performed under a previous required-inspection finding — again with separation honored.
Tool-calibration + training records
The §135.427(b)(5) precision-tool calibration certificates and due dates, and the §135.433 training records for inspection personnel.
The RII program does not live in isolation. Its sign-offs feed the §135.439 maintenance records and the §135.443 airworthiness release; its entries must satisfy the §43.9 entry-content rules; and major repairs and alterations that are RIIs also generate Form 337 records. For the full cross-vertical recordkeeping master list, see What Records Must a Part 135 Operator Keep.
Keep your RII program records audit-ready
FileFlo is a compliance document intelligence platform — a read-only proof layer that classifies and tracks the records your RII program produces. It does not perform required inspections, decide who is authorized, sign anything, or connect to your maintenance-tracking system. You upload the documents; FileFlo:
- Classifies each document against the governing CFR (§135.427, §135.429, §135.423, §135.433)
- Tracks expirations — inspector authorization currency, tool-calibration due dates, training renewals
- Sends 90/60/30-day expiration alerts before an authorization or calibration lapses — not the day after
- Assembles an organized RII-program binder — manual designations, the authorized-personnel list, buy-back and calibration records — for an FAA surveillance review
FileFlo sits alongside your Director of Maintenance, your chief inspector, your A&P/IA personnel, and your Part 145 repair station — it keeps the documents that prove the program, it does not run it or make the authorization decisions. Starter $89/mo · Professional $299/mo · 5-day free trial, no credit card required.
Related Aviation Recordkeeping Guides
Frequently Asked Questions
What is a Required Inspection Item (RII) under Part 135?
A Required Inspection Item is an item of maintenance or alteration that must be inspected by a second, authorized person before the aircraft returns to service. The designation comes from 14 CFR §135.427(b)(2), which requires the certificate holder to put in its manual "a designation of the items of maintenance and alteration that must be inspected (required inspections) including at least those that could result in a failure, malfunction, or defect endangering the safe operation of the aircraft, if not performed properly or if improper parts or materials are used." In plain terms: any task where a mistake could threaten safe flight is a candidate to be designated an RII. The classic examples are flight-control rigging, primary structure, engine and propeller installations, and other work where a single undetected error is catastrophic. The RII concept applies to the 10-or-more-seat maintenance program; it is not a free-standing rule for nine-or-fewer-seat aircraft.
What is the separation-of-authority rule for required inspections?
It is the core integrity rule of the RII program, and it lives in 14 CFR §135.429(c): "No person may perform a required inspection if that person performed the item of work required to be inspected." The mechanic who did the work cannot be the inspector who signs it off as a required inspection — the two functions must be performed by two different qualified people. The rule is reinforced organizationally by §135.423(c), which requires a certificate holder that performs both required inspections and other maintenance to organize the work so as to separate the required-inspection functions from the other maintenance functions, with that separation existing "below the level of administrative control at which overall responsibility for the required inspection functions and other maintenance, preventive maintenance, and alterations is exercised." So the separation is built into both the individual act (you cannot inspect your own work) and the org chart (inspection and maintenance report up through separate chains below the top).
Who maintains the list of personnel authorized to perform required inspections?
The certificate holder does. Under 14 CFR §135.429(e), "Each certificate holder shall maintain, or shall determine that each person with whom it arranges to perform its required inspections maintains, a current listing of persons who have been trained, qualified, and authorized to conduct required inspections." If you contract your required inspections to an outside organization, you must either keep the listing yourself or confirm that the contractor keeps it. In addition, §135.427(b)(3) requires the manual to designate, by occupational title, the personnel authorized to perform each required inspection, and §135.427(a) requires the manual to list the outside persons with whom the certificate holder has arranged to perform any of its required inspections, other maintenance, preventive maintenance, or alterations. The listing is not a static document — it has to be current, because authorizations are added and removed as people are trained, change roles, or leave.
Where in the maintenance manual must the RII program appear?
The RII program is documented across several paragraphs of 14 CFR §135.427(b). Paragraph (b)(2) is the designation of the required inspection items themselves. Paragraph (b)(3) is the method of performing required inspections and the designation by occupational title of personnel authorized to perform each required inspection. Paragraph (b)(4) covers the procedures for the reinspection of work performed under previous required inspection findings — the buy-back procedures. Paragraph (b)(5) covers the procedures, standards, and limits necessary for required inspections and for the acceptance or rejection of the items inspected, plus the periodic inspection and calibration of precision tools, measuring devices, and test equipment. Paragraph (b)(6) requires procedures to ensure that all required inspections are performed. Separately, §135.427(a) ties the manual back to the organizational chart required by §135.423 and to the list of outside persons performing the work.
What are buy-back procedures and why do they matter for RII?
A "buy-back" is the reinspection of work that an inspector rejected on a previous required inspection. When a required inspection finds a discrepancy, the discrepancy is corrected and then the corrected work must be reinspected. 14 CFR §135.427(b)(4) requires the certificate holder to put in its manual "procedures for the reinspection of work performed under previous required inspection findings (buy-back procedures)." The reason it matters for the RII program is that a buy-back is itself a required inspection — so the separation-of-authority rule in §135.429(c) still applies: the person who corrected the rejected work cannot be the person who buys it back. Buy-back records are a frequent focus in an FAA records review because they are where the loop on a safety-critical discrepancy is closed.
Does the RII program apply to nine-or-fewer-seat Part 135 aircraft?
Not as such. The required-inspection-item framework in §135.427 and §135.429 is part of the maintenance program that 14 CFR §135.411(a)(2) imposes on aircraft type certificated for a passenger seating configuration of 10 seats or more (excluding any pilot seat) — the program built from §§135.415, 135.417, and 135.423 through 135.443. Aircraft type certificated for nine seats or fewer are maintained under §135.411(a)(1), which points to parts 91 and 43 plus §§135.415, 135.417, 135.421, and 135.422; those aircraft do not carry a designated RII program in the §135.427 sense, though their work is still inspected and returned to service under the part 43 entry rules. A nine-or-fewer-seat operator that elects the §135.411(a)(2) program (permitted by §135.411(b)) takes on the RII obligations with it.
What qualifications must a required inspection person have under §135.429?
Three layers. First, under 14 CFR §135.429(a), no person may use any person to perform required inspections unless the person performing the inspection is appropriately certificated, properly trained, qualified, and authorized to do so. Second, under §135.429(b), no person may allow any person to perform a required inspection unless, at the time, the person performing that inspection is under the supervision and control of an inspection unit. Third, the training underpinning that competence comes from §135.433, the maintenance and preventive maintenance training program, which requires a program ensuring that each person — including inspection personnel — who determines the adequacy of work done is fully informed about procedures, techniques, and new equipment, and is competent to perform their duties. The certificated/trained/qualified/authorized status of each RII person is exactly what the §135.429(e) listing records.
How does FileFlo help with RII program records?
FileFlo is a compliance document intelligence platform — a read-only proof layer. It does not perform required inspections, sign airworthiness releases, decide who is authorized, or connect to your maintenance-tracking system. What it does is keep the documentary evidence of the RII program audit-ready: it classifies the manual sections, the §135.429(e) authorized-personnel listing, the RII training records, the buy-back records, and the tool-calibration records against the governing CFR; it tracks expirations such as inspector authorization currency and calibration due dates; and it can assemble those documents into an organized binder for an FAA surveillance review. The judgment about whether an item is an RII, who may inspect it, and whether the separation rule was honored stays with your Director of Maintenance, your chief inspector, and your A&P/IA personnel — FileFlo proves the records exist and are current.
More Part 135 & Aviation Compliance Guides
Part 135 Maintenance Recordkeeping (CAMP)
The §§135.423–443 program, the §135.431 CASS, and the §135.439 records the RII sign-offs feed
What Records Must a Part 135 Operator Keep
The master index: every Part 135 record mapped to its CFR cite, owner, and retention period
What a §43.9 Maintenance Entry Must Contain
The required elements of every compliant maintenance record entry — and where §43.11 takes over for inspections
Part 91.409 Inspection Requirements
Annual, 100-hour, progressive, and AAIP — who signs each and the records they produce
Document AD Compliance for a Ramp Check
Logbook wording and recurring-AD next-due math for the status-record set
Prepare for a Part 135 FAA Surveillance Audit
The documents an FAA inspector requests during a SAS surveillance visit, in order
Part 145 Repair Station Recordkeeping
How the contracted shops that perform your required inspections keep their own records
The Part 145 Audit Binder
Every document an FAA inspector asks for during a Part 145 surveillance visit, in order
FAA Form 337 — Major Repair & Alteration
When a required-inspection item is also a major repair or alteration requiring a 337
What Is Operational Control in Part 135
The accountability cousin of maintenance separation — defined in 14 CFR §1.1
Part 135 Training Program Recordkeeping
How §135.433 maintenance training fits the broader Part 135 training-records picture
Life-Limited Parts Records
The status records that an RII installation must trace — life limits, time since new, and disposition
Prove your RII program before the FAA asks
FileFlo classifies your RII-program documents against 14 CFR §135.427, §135.429, and §135.433, tracks inspector-authorization currency and tool-calibration due dates, and sends 90/60/30-day alerts before anything lapses. Keep the RII designation list, the authorized-personnel list, buy-back records, and calibration certificates documented and organized by CFR paragraph — ready for a surveillance visit.
Starter $89/mo · Professional $299/mo · 5-day free trial · No credit card required · Cancel anytime