Explainer
Engine and Propeller Manuals: What the FAA Requires
The Short Answer
Two Rules, Two Appendices
14 CFR 33.4 (engines) and 35.4 (propellers) each tell the applicant to prepare Instructions for Continued Airworthiness (ICA) in accordance with Appendix A to that part, in a form acceptable to the Administrator. The instructions may be incomplete at type certification if a program exists to complete them before delivery of the first aircraft with the product installed, or issuance of a standard airworthiness certificate for that aircraft, whichever is later.
The appendices are where the manual list lives. For an engine: a maintenance manual or section, an overhaul manual or section, and an Airworthiness Limitations section. For a propeller: a maintenance section, an overhaul section, and the same limitations section. The general idea of ICA is covered in instructions for continued airworthiness. This page covers what changes when the product is an engine or propeller.
Engines
The Engine Maintenance Manual
Appendix A to Part 33, paragraph A33.3(a), lists what the maintenance manual or section must contain, prepared in English. In outline:
- Description and installation
- Engine features, components, systems, and installations, plus installation procedures for uncrating, deinhibiting, acceptance checking, lifting, and attaching accessories.
- Operation and servicing
- How the engine and its systems operate, how to start, run, test, and stop it, and servicing data: service points, capacities, fluids, pressures, lubrication points, and equipment.
- Scheduling and inspection program
- Recommended periods for cleaning, inspecting, adjusting, testing, and lubricating, with wear tolerances and the degree of work, plus recommended overhaul periods, cross-references to the Airworthiness Limitations section, and an inspection program with the frequency and extent of inspections.
- Troubleshooting, removal and replacement
- Probable malfunctions, how to recognize them and the remedy, the order and method of removing the engine and its parts and replacing parts, and instructions for ground handling, crating, and shipping.
- Tools and equipment
- A list of the tools and equipment needed for maintenance and directions for using them.
Scheduling may point to an accessory, instrument, or equipment maker as the source, but only where the applicant shows the item is exceptionally complex and needs specialized techniques, test equipment, or expertise. For an engine seeking installation on an ETOPS airplane, A33.3(c) adds engine condition monitoring procedures that can show, before flight, whether the engine can deliver the power or thrust, bleed air, and power extraction needed for an engine-inoperative diversion.
Overhaul
The Engine Overhaul Manual
Paragraph A33.3(b) covers the work done with the engine off the aircraft:
- Teardown and inspection
- The order and method of disassembly, and cleaning and inspection instructions: materials, apparatus, methods, precautions, and the methods of overhaul inspection.
- Fits, clearances, and repairs
- All fits and clearances relevant to overhaul, repair methods for worn or substandard parts, and the information needed to decide when a part must be replaced.
- Assembly, test, storage
- The order and method of assembly at overhaul, instructions for testing after overhaul, storage preparation with any storage limits, and a list of overhaul tools.
AC 33.4-1 asks the type certificate holder to define what level of inspection and repair or replacement counts as an overhaul for that engine, because the ICA is where that definition has to live. It also says the overhaul manual should always be provided separately by the engine holder, since it deals with uninstalled engines, and that the overhaul section may follow entry into service on an FAA-accepted schedule, normally within six months, with the type certificate data sheet noting that overhaul and heavy maintenance are not permitted until the manual exists. The AC is guidance, not a rule.
Propellers
Propeller Sections
Appendix A to Part 35 mirrors the engine list in a lighter form. The maintenance section covers description, controls and operation, uncrating, acceptance checking, lifting and installing, operational checks, scheduling with an inspection program and overhaul periods, troubleshooting, removal and replacement, and special tools. The overhaul section covers disassembly, cleaning and inspection, fits and clearances, repair methods, assembly, testing after overhaul, storage, and overhaul tools.
AC 35.4-1 follows the same pattern as the engine AC: the holder should provide a separate propeller overhaul manual, may defer it on an FAA-accepted schedule, and should define what an overhaul is for that propeller. Installation and operation instructions sit in a separate rule, 35.3, which requires approved instructions covering the interfaces with the airplane and engine, the limitations, and the approved hydraulic fluids.
Limitations
The Airworthiness Limitations Section
Both appendices require a section titled Airworthiness Limitations, segregated and clearly distinguishable from the rest of the manual. It sets out each mandatory replacement time, inspection interval, and related procedure required for type certification, and carries a prominent statement that it is FAA approved and specifies maintenance required under 14 CFR 43.16 and 91.403 unless an alternative program has been FAA approved. If the engine ICA span multiple documents, this section goes in the principal manual.
For rotorcraft engines with 30-second or 2-minute one-engine-inoperative ratings, A33.4 also requires the mandatory post-flight inspections and maintenance actions tied to those ratings, validated by the applicant and backed by an in-service evaluation program. The maintenance manual cross-references the section wherever an overhaul time or inspection is a limitation. More in the Airworthiness Limitations section.
Aircraft Level
How They Fit the Aircraft ICA
The aircraft ICA must cover each engine and propeller on the aircraft, and Order 8110.54A says that where the manufacturer supplies none, the aircraft ICA must carry the essential information. The engine and propeller ICA are the source for that content, not a separate copy to be rewritten.
AC 33.4-1 explains the working arrangement. The engine holder may furnish its maintenance instructions to the aircraft manufacturer for incorporation into the aircraft maintenance manual. If so, the aircraft manufacturer adopts them without altering them, only the engine holder may change that portion, and the engine holder keeps a program, acceptable to the FAA, to control and distribute it. Where the engine holder cannot run such a program, it produces and distributes its own engine ICA.
Supplier manuals work the same way. Where the engine ICA refer to a component manual, that manual becomes part of the complete ICA, so the reference should cite its revision level and date and the holder remains responsible. Order 8110.54A chapter 5 adds that changes to the ICA made by service documents are incorporated by reference as AC 33.4-1 and AC 35.4-1 describe. For the aircraft-side view, see what an aircraft maintenance manual is and, for modifiers, ICA for STC holders.
In the Shop
The Set an Engine Shop Actually Uses
Regulation names two manuals. A working engine or propeller program uses a set:
- Engine or propeller maintenance manual
- The principal manual for work on the installed product and its day-to-day servicing. Often published as an engine section inside the aircraft maintenance manual as well as on its own.
- Overhaul manual
- What a shop follows with the product off the aircraft. Provided separately, because it covers uninstalled engines and propellers.
- Installation and operating instructions
- The approved instructions of 33.5 or 35.3, which the aircraft builder or modifier uses to install the product and which define its interfaces and limits.
- Component and accessory manuals
- Supplier manuals the principal manual points to. Once referenced, they are part of the ICA, at the revision and date cited.
- Illustrated parts data
- A parts configuration control method, such as an illustrated parts catalog, is encouraged by Order 8110.54A but not required by the appendices.
- Service bulletins and service letters
- A separate class of service document. They change the ICA only where the ICA incorporates them by reference under the criteria in AC 33.4-1.
The practical rule for whoever turns the wrench is 14 CFR 43.13(a): use the methods, techniques, and practices in the current manufacturer's maintenance manual or ICA, or other methods acceptable to the Administrator. "Current" makes revision control part of the job; see obtaining OEM manuals, aircraft manual types, and service bulletin currency. Operators under Part 121 or 135 may carry their own manual under 43.13(c); see operator maintenance manuals.
Shakewell writes instructions for continued airworthiness and maintenance and overhaul manuals for engine and propeller manufacturers.
FAQ
Questions We Hear
What manuals must an engine manufacturer provide?
Section 33.4 requires Instructions for Continued Airworthiness prepared under Appendix A to Part 33. That appendix calls for an Engine Maintenance Manual or Section and an Engine Overhaul Manual or Section, an Airworthiness Limitations section, and, for engines seeking ETOPS eligibility, engine condition monitoring procedures. Section 33.5 separately requires approved instructions for installing and operating the engine.
Is an engine manual the same as the aircraft maintenance manual?
No. The aircraft ICA must include the ICA for each engine and propeller, and AC 33.4-1 allows the engine type certificate holder to furnish its maintenance instructions for incorporation into the aircraft maintenance manual. The engine holder still controls that content, and only the engine holder may change it. The overhaul manual is provided separately.
Does the overhaul manual have to exist before the engine enters service?
AC 33.4-1 says the overhaul section may be delayed until after entry into service on a schedule the FAA accepts, normally within six months. Until it is complete, the AC says no person should overhaul the engine or perform heavy maintenance, and the type certificate data sheet should say so. AC 35.4-1 gives the same guidance for propellers. An AC is guidance, not a rule; read the type certificate data sheet for the product you hold.
What goes in an engine or propeller Airworthiness Limitations section?
Each mandatory replacement time, inspection interval, and related procedure required for type certification, in a segregated section that carries the prescribed statement that it is FAA approved and specifies maintenance required under 14 CFR 43.16 and 91.403. For rotorcraft engines with 30-second or 2-minute one-engine-inoperative ratings, it also prescribes the mandatory post-flight inspections and maintenance actions tied to using those ratings.
Can a service bulletin change the engine manual?
Only if the manual incorporates it by reference, and AC 33.4-1 sets conditions: the reference must be version specific (not "the latest revision"), the technical content must be FAA approved, and the bulletin must reach all owners. The AC says temporary revisions to the manual are more appropriate than bulletins for this purpose.
Which manual must a shop follow when it works on an engine?
14 CFR 43.13(a) requires the methods, techniques, and practices in the current manufacturer's maintenance manual or ICA, or other methods acceptable to the Administrator. Part 121 and 135 operators may also have methods in their own manual under 43.13(c). Read the rule and your approvals for how they apply to your work.
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