Part 135 Maintenance Requirements: Inspections, Records, and ADs

Part 135 maintenance requirements are the airworthiness rules in Subpart J of 14 CFR Part 135 that every commuter and on-demand operator must follow, and they split into two tracks based on how many passenger seats the aircraft is type-certificated to carry. Aircraft with nine seats or fewer are maintained under Parts 91 and 43 with a handful of Part 135 add-ons. Aircraft with ten or more seats must run under a full continuous-airworthiness program covering organization, inspections, personnel, records, and returns to service. Either way, the certificate holder is the responsible party. Contracting out the wrenching does not shift that responsibility.¹

How the Two Tracks Are Divided

Subpart J applies to all aircraft operated under a Part 135 certificate. The dividing line uses the type-certificated passenger seating configuration, excluding pilot seats.²³

Nine seats or fewer: Maintained under Parts 91 and 43, plus Part 135 obligations for service difficulty reports, mechanical interruption summaries, and the manufacturer’s recommended maintenance program. Operators may also apply for an Approved Aircraft Inspection Program.
Ten or more seats: Maintained under the detailed program in sections 135.423 through 135.443, industry-referred to as a Continuous Airworthiness Maintenance Program, or CAMP.

An operator with smaller aircraft may voluntarily opt into the more robust ten-seat program. Certain twin-engine extended-range operations require the ten-seat track along with the additional requirements in Appendix G.³

The certificate holder is primarily responsible for the airworthiness of every aircraft in its fleet, including airframes, engines, propellers, rotors, appliances, and parts. When another person performs the work, the certificate holder must ensure the work is done under its own manual and in compliance with the regulations.¹ Farming out a heavy check to a repair station does not relieve accountability. If the repair station misses something, the FAA looks to the certificate holder first.

Requirements for Aircraft With Nine or Fewer Seats

Operators in this category follow the general inspection and maintenance standards of Parts 91 and 43. On top of that, they must follow the manufacturer’s recommended maintenance program for each engine, propeller, rotor, and item of emergency equipment, or an FAA-approved alternative.⁴

Single-engine aircraft used for passenger-carrying IFR flights carry an extra obligation. The operator must use either the manufacturer’s recommended engine trend monitoring program, including oil analysis where appropriate, or an FAA-approved monitoring program with oil analysis at least every 100 hours. Each test and inspection result must be recorded in the engine maintenance records.⁴

The Approved Aircraft Inspection Program Option

Small-aircraft operators may apply for an Approved Aircraft Inspection Program, and the FAA may require one if it decides standard Part 91 inspections are inadequate. Qualifying requires exclusive use of at least one aircraft of the make and model covered.⁵

The submitted program must include detailed inspection instructions and tests covering every part and area of the airframe, engines, propellers, rotors, appliances, and emergency equipment; an inspection schedule expressed in time in service, calendar time, system operations, or a combination; and procedures for recording, correcting, or deferring discrepancies found during inspections. Once approved, the program becomes part of the operator’s manual, and the FAA can require revisions if it later finds the program inadequate.⁵

Requirements for Aircraft With Ten or More Seats

The larger-aircraft program is a documented, top-to-bottom system spelled out in the certificate holder’s manual. At a minimum it must address:

Routine and nonroutine maintenance methods for both scheduled and unscheduled work.
Designation of required inspection items, meaning every task that could endanger safe operation if done improperly or with the wrong parts.
The procedures for conducting required inspections, and the job titles authorized to perform each one.
Buy-back procedures for reinspecting work that follows a required-inspection finding.
Standards and limits for accepting or rejecting inspected items, plus calibration schedules for precision tools and test equipment.
Procedures to ensure incomplete maintenance is properly finished before an aircraft returns to service.
Policies for any maintenance performed by an outside provider, acceptable to the FAA, that ensure the work follows the certificate holder’s own program.

The manual must also carry an organizational chart and a list of every person or entity authorized to perform inspections, maintenance, and alterations on the operator’s behalf.⁶

Required Inspections and the Separation Rule

Certain tasks are designated “required inspections” because errors in them could make the aircraft unsafe. Two rules govern how those inspections happen.

First, the person who performed the work cannot inspect it. If a mechanic installs a flight control component, a different qualified individual must perform the required inspection.⁷ The manual must include explicit language enforcing that separation and shielding inspectors from being overruled by anyone outside their supervisory chain.⁶

Second, at the organizational level, operators that perform both required inspections and other maintenance must keep the inspection and maintenance functions organizationally separate. The split has to occur below the management level that oversees both, so the inspectors do not report to the same supervisor as the mechanics.⁸

One narrow exception exists for rotorcraft operating in remote locations where no other qualified person is available. The FAA may approve procedures allowing a properly trained pilot employed by the certificate holder to perform required inspections following a mechanical interruption. Even then, a certificated mechanic must reinspect the item after each subsequent flight, and any flight-control-system work requires a flight test and reinspection before return to service.⁷

Personnel, Certificates, and Return to Service

Every person directly in charge of maintenance, preventive maintenance, or alterations must hold an appropriate airman certificate, as must every person performing required inspections. “Directly in charge” means responsibility for the work of a shop or station. The person does not need to stand over each worker at all times, but must be available for consultation on anything above the wrench-turner’s authority.⁹

The certificate holder may perform the work itself or arrange for others to do it, provided the work follows the maintenance manual. Authorized personnel may approve routine maintenance for return to service. Major repairs and major alterations carry a higher bar: they must use technical data approved by the FAA.¹⁰

No aircraft may fly after maintenance, preventive maintenance, or alterations until the certificate holder prepares (or has the maintenance provider prepare) an airworthiness release or an appropriate entry in the aircraft maintenance log. That release or log entry must certify four things:

The work followed the certificate holder’s manual.
All required inspection items were inspected by an authorized person who confirmed the work was completed satisfactorily.
No known condition exists that would make the aircraft unairworthy.
As far as the work performed is concerned, the aircraft is in condition for safe operation.

Only an authorized certificated mechanic or repairman may sign. A repairman’s authority is limited to work within the scope of their employment and certification. The manual can state that an authorized signature constitutes full certification, so the four conditions do not have to be rewritten every time.¹¹

Airworthiness Directives

Airworthiness Directives are mandatory rules the FAA issues when it finds an unsafe condition in a product that is likely to exist or develop in other products of the same design.¹² Operating an aircraft that does not comply with an applicable AD is a violation.¹³

The operator’s maintenance records must track the current status of every applicable AD, including the date and method of compliance and, for recurring ADs, the next-action date.¹⁴ Manufacturer Service Bulletins are not legally enforceable the way ADs are, but a well-run program evaluates them and adopts those that affect safety or appear likely to become mandatory.

Service Difficulty Reports

Part 135 operators must report certain failures, malfunctions, and defects to the FAA’s office in Oklahoma City. The reportable list covers a specific set of in-flight events: engine shutdowns, fires (and whether fire-warning systems worked), false fire warnings, exhaust system damage, smoke or toxic fumes in the cabin or cockpit, landing gear malfunctions, brake failures during ground operations, and any event requiring emergency action in flight.¹⁵

Beyond that list, operators must report any other failure or defect that, in the operator’s judgment, has endangered or may endanger safe operation. Reports cover each 24-hour period beginning at 0900 local time and must be submitted within 96 hours. Reports due on weekends may be filed the following Monday, and holiday reports may wait until the next business day.¹⁵

Missed service difficulty reports rarely draw attention until an accident investigation reveals a pattern of unreported issues. At that point the consequences compound quickly.

Maintenance Records

Part 135 maintenance generates two layers of documentation: the individual work entries required by Part 43, and the fleet-level records required by Part 135.

Each person who performs maintenance, preventive maintenance, rebuilding, or an alteration must create a record entry with a description of the work, the completion date, the name of the person who did the work (if different from the person approving it), and the signature, certificate number, and certificate type of the person approving the return to service. That signature is the return-to-service approval, but only for the specific work described.¹⁶

At the fleet level, the certificate holder must keep records using the system specified in its manual. They fall into two retention categories:

Temporary records: Everything needed to show the airworthiness release requirements were met. Kept until the work is repeated or superseded, or for one year after the work is performed, whichever comes first. Records of the last complete overhaul of each airframe, engine, propeller, rotor, and appliance are kept until superseded by an equivalent overhaul.
Permanent records: Total time in service of the airframe, engine, propeller, and rotor; current status of all life-limited parts; time since last overhaul of every time-limited component; current inspection status; current status of all applicable ADs; and a list of current major alterations and repairs. Retained and transferred with the aircraft on sale.¹⁴

When a certificate holder sells a U.S.-registered aircraft, both the permanent and temporary records go to the purchaser at the time of sale. Records may be plain language or coded, as long as the system preserves and retrieves them in a way acceptable to the FAA. The purchaser may agree to let the seller keep physical custody of the temporary records, but the new owner still has to make them available for FAA or NTSB inspection on request.¹⁷

What Noncompliance Costs

Maintenance violations under Part 135 can produce FAA enforcement ranging from warning letters to certificate suspension or revocation, and the FAA also has authority to impose civil penalties. For entities that are not individuals or small businesses, the maximum civil penalty can reach $75,000 per violation. Individuals and small business concerns face a lower cap of $1,100 per violation for most offenses, or up to $10,000 per violation for certain categories.¹⁸

The FAA’s sharpest tool is the certificate action. Suspending or revoking a Part 135 certificate shuts down the operation. Chronic record-keeping failures, unreported service difficulties, and patterns of deferred maintenance that cross from acceptable to negligent are the findings that escalate from a letter of investigation into a proposed certificate action. Getting the maintenance program right up front almost always costs less than fighting an enforcement case later.

1
eCFR. 14 CFR 135.413 – Responsibility for Airworthiness
2
Federal Aviation Administration. General Information – Part 135 Certification
3
eCFR. 14 CFR 135.411 – Applicability
4
eCFR. 14 CFR 135.421 – Additional Maintenance Requirements
5
eCFR. 14 CFR 135.419 – Approved Aircraft Inspection Program
6
eCFR. 14 CFR 135.427 – Manual Requirements
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eCFR. 14 CFR 135.429 – Required Inspection Items
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eCFR. 14 CFR 135.423 – Maintenance Organization Requirements
9
eCFR. 14 CFR 135.435 – Certificate Requirements
10
eCFR. 14 CFR 135.437 – Authority to Perform and Approve Maintenance
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eCFR. 14 CFR 135.443 – Airworthiness Release or Aircraft Maintenance Log Entry
12
eCFR. 14 CFR 39.5 – When Does FAA Issue Airworthiness Directives
13
eCFR. 14 CFR 39.7 – What Is the Legal Effect of Failing to Comply With an Airworthiness Directive
14
eCFR. 14 CFR 135.439 – Maintenance Recording Requirements
15
eCFR. 14 CFR 135.415 – Service Difficulty Reports
16
eCFR. 14 CFR 43.9 – Content, Form, and Disposition of Maintenance Records
17
eCFR. 14 CFR 135.441 – Transfer of Maintenance Records
18
Office of the Law Revision Counsel. 49 USC 46301 – General Civil Penalties