AC 35-1A

U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Certification of Propellers Date: 10/11/2018 Initiated By: AIR-6A0 AC No: 35-1A Change No.: N/A This AC describes an acceptable method, but not the only method, that may be used to demonstrate compliance to the propeller type certification requirements of Title 14, Code of Federal Regulations (14 CFR) part 35.

If you have suggestions for improving this AC, you may use the Advisory Circular Feedback Form at the end of this AC.

Dr. Michael C. Romanowski Director, Policy and Innovation Division Aircraft Certification Service

i Table of Contents

Chapter 1. Introduction1-1

1.1 Purpose1-1

1.2 Applicability1-1

1.3 Cacellation1-1

1.4 Related Reading Materials1-1

1.5 Definitions1-2

1.6 Background1-4

Chapter 2. Guidance for Subpart A - General2-1

2.1 Section 35.1, Applicability2-1

2.2 Section 35.2, Propeller configuration2-2

2.3 Section 35.3, Instructions for propeller installation and operation2-2

2.4 Section 35.4, Instructions for Continued Airworthiness2-3

2.5 Section 35.5, Propeller ratings and operating limitations2-3

2.6 Section 35.7, Features and characteristics2-4

Chapter 3. Guidance for Subpart B – Design and Construction3-1

3.1 Section 35.15, Safety analysis3-1

3.2 Section 35.16, Propeller critical parts3-7

3.3 Section 35.17, Materials and manufacturing methods3-7

3.4 Section 35.19, Durability3-9

3.5 Section 35.21, Variable and reversible pitch propellers3-9

3.6 Section 35.22, Feathering propellers3-10

3.7 Section 35.23, Propeller control system3-10

3.8 Section 35.24, Strength3-10

Chapter 4. Guidance for Subpart C – Type Substantiation4-1

4.1 Section 35.33, General4-1

4.2 Section 35.34, Inspection, adjustments, and repairs4-1

4.3 Section 35.35, Centrifugal load tests4-1

4.4 Section 35.36, Bird impact4-2

4.5 Section 35.37, Fatigue limits and evaluation4-3

4.6 Section 35.38, Lightning strike4-3

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4.7 Section 35.39, Endurance test4-4

4.8 Section 35.40, Functional test4-5

4.9 Section 35.41, Overspeed and overtorque4-6

4.10 Section 35.42, Components of the propeller control system4-7

4.11 Section 35.43, Propeller hydraulic components4-7

1-1 1 INTRODUCTION

1.1 Purpose.

This AC describes an acceptable method, but not the only method, that may be used to demonstrate compliance to the propeller type certification requirements of Title 14, Code of Federal Regulations (14 CFR) part 35.

1.2 Applicability.

1.2.1 The guidance in this AC is for propeller manufacturers, modifiers, foreign regulatory authorities, Federal Aviation Administration (FAA) propeller type certification engineers, and FAA designees.

1.2.2 This AC is not mandatory and does not constitute a regulation. This AC describes an acceptable means, but not the only means, to demonstrate compliance to the propeller type certification requirements of 14 CFR part 35. However, if you use the means described in the AC, you must follow it in all important respects. When the method of compliance in this AC is used, terms such as “should,” “may,” and “must” are used only in the sense of ensuring applicability to this particular method of compliance. The FAA will consider other means of showing compliance that an applicant may elect to present. While these guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with the relevant regulations.

If, however, the FAA becomes aware of circumstances that convince us that following this AC would not result in compliance with the applicable regulations, we will not be bound by the terms of this AC, and we may require additional substantiation as a basis for finding compliance.

1.2.3 This material in this AC does not change or create any additional regulatory requirements, nor does it authorize changes in, or permit deviations from, existing regulatory requirements.

1.3 Cancellation.

This AC cancels AC 35-1, Certification of Propellers, issued December 29, 2008.

1.4 Related Reading Materials.

The following materials are referenced in this document. Unless otherwise indicated, you should use the latest revision from the FAA.

1.4.1 Title 14, Code of Federal Regulations (CFRs).

 Part 21, Certification Procedures for Products and Parts.

 Part 23, Airworthiness Standards: Normal Category Airplanes.

 Part 25, Airworthiness Standards: Transport Category Airplanes.

1-2  Part 33, Airworthiness Standards: Aircraft Engines.

 Part 35, Airworthiness Standards: Propellers.

 Part 45, Identification and Registration Marking.

1.4.2 FAA Documents.

 AC 20-53, Protection of Aircraft Fuel Systems against Fuel Vapor Ignition Caused by Lightning.

 AC 20-107, Composite Aircraft Structure.

 AC 20-136, Aircraft Electrical and Electronic System Lightning Protection.

 AC 20-155, Industry Documents to Support Aircraft Lightning Protection Certification.

 AC 35.4-1, Propeller Instructions for Continued Airworthiness.

 AC 35.16-1, Propeller Critical Parts.

 AC 35.23-1, Guidance Material for 14 CFR § 35.23, Propeller Control System.

 AC 35.37-1, Propeller Fatigue Limits and Evaluation.

 Order 8110.4, Type Certification.

 PS-ACE 100-2002-006, Material Qualification and Equivalency for Polymer Matrix Composite Material Systems.

1.4.3 Non-FAA Documents.

 EASA Certification Specifications for Propellers (CS-P).

 RTCA/DO-160, Environmental Conditions and Test Procedures for Airborne Equipment.

 SAE, Composite Materials Handbook-17 (CMH-17).

1.5 Definitions.

 Analysis and Assessment. The two terms are, to some extent, interchangeable.

However, “analysis” generally implies a specific and detailed evaluation, while “assessment” implies a general or broader evaluation that may include one or more types of analysis. In practice, the distinction comes from the specific application (for example, functional hazard analysis (FHA), fault tree analysis (FTA), failure mode and effects analysis (FMEA), and Markov analysis).

 Beta Control. A system by which the propeller blade angle is directly selected.

For constant speed propellers, beta control is normally used during ground handling, including reverse pitch angles.

 Blade Retention. Area of the blade that transmits blade centrifugal and bending loads to the hub. Included in the retention are bearing races and other associated components used for the transmission of loads to the hub.

1-3  Check. An examination, inspection, or test that determines physical integrity, functional capability or both.

 Conventional. The same as, or closely similar to, previously approved systems, components, or attributes that are commonly used.

 Dormant failure. A failure the effect of which is not detected for a given period of time.

 Failure Condition. A condition with direct, consequential propeller-level effects caused or contributed by one or more failures.

 Failure Mode. The mechanism of the failure or the manner in which an item or function can fail.

 Feather. Moving the blade angle to feathered pitch.

 Feathered Pitch. The pitch setting that corresponds to an in-flight windmilling torque and rotational speed of approximately zero.

 Fixed Pitch Wood Propellers of Conventional Design. A propeller that has two or four blades that are constructed from one piece of laminated wood construction with a surface coating that only provides environmental protection and does not contribute to propeller strength. A fixed pitch propeller with a composite shell over a wood core is not a conventional design when the composite shell contributes to the strength and frequency response of the propeller. A fixed pitch wooden propeller with a fabric or composite covering that does not alter the structure for environmental protection is of conventional design.

 Fixed Pitch Metal Propellers of Conventional Design. A propeller that has two blades that are constructed from one piece of solid metal construction.

 Ground Adjustable Pitch Propeller. A propeller whose pitch setting can be changed during field maintenance, but not when the propeller is rotating.

 Ground Idle. The power lever position, which results in zero or nearly zero thrust, while the aircraft is on the ground and not moving.

 In-Flight Low-Pitch Position. The minimum pitch permitted in-flight by the control system in normal operation.

 Pitch. The propeller blade angle that is measured in a manner and at a radius stated by the manufacturer and specified in the appropriate propeller manual.

 Pitch Control System. The components of the propeller system that control pitch position, including, but not limited to, governors, pitch change assemblies, pitch locks, mechanical stops, and feathering system components.

 Primary Failure. Failure of a part that is not the result of a prior failure of another part or system.

 Propeller. The propeller as defined in 14 CFR 35.1(d) consists of those components listed in the propeller type design.

1-4  Propeller System. The propeller system as defined in § 35.1(d) consists of the propeller and all the components necessary for its functioning, but not necessarily included in the propeller type design.

 Reverse Pitch. The propeller blade angle used for producing reverse thrust with a propeller. Typically, any blade angle below ground idle blade angle.

 Reversible Pitch Propeller. A propeller in which blades can be rotated to a reverse pitch blade angle while operating.

1.6 Background.

This AC was originally developed in conjunction with a major revision to the airworthiness standards for airplane propellers in amendment 8 to 14 CFR part 35.

Amendment 35-8 was published to the Federal Register on November 06, 2008 (73 FR 65968). Since original issuance, industry and the FAA have gained experience with the application of amendment 8. In addition, the propeller regulations were revised to include critical parts requirements in amendment 9a. Amendment 35-9a was published to the Federal Register on July 26, 2013 (78 FR 45052).

2-1 2 GUIDANCE FOR SUBPART A - GENERAL

2.1 Section 35.1, Applicability.

2.1.1 Propeller Type Certificate.

Propeller type certificates are issued independently from the airplane and engine under 14 CFR part 35. Part 35 does not require engine/aircraft applications be listed on the propeller type certificate data sheet (TCDS). This allows manufacturers to produce propellers for a variety of different aircraft and engine installations. Applicants may request that propeller models that incorporate different features, such as blade models, flange, or control configurations be added to the propeller type certificates (TC) after issuance.

2.1.2 Special Airworthiness Certificates.

The phrase “or compliance is not required for installation on that airplane” in § 35.1(c) refers to airplanes that are issued special airworthiness certificates. These airplanes include those with primary, restricted, surplus aircraft of the Armed Forces, limited, light-sport, and provisional airworthiness certificates; special flight permits; and experimental certificates. Exceptions to this may apply if the Administrator finds that compliance to 14 CFR 23.2400(c)(4) or 14 CFR 25.907 is required. These exceptions may include primary, restricted, surplus aircraft of the Armed Forces, and limited category airplanes. An airplane with a special (experimental) airworthiness certificate as defined in § 21.191, Experimental certificates, does not need to show compliance with the requirements of § 23.2400(c)(4) or § 25.907.

2.1.3 Propeller System and Propeller Type Design.

Title 14 CFR part 35 distinguishes between the propeller and the propeller system because some components required to operate the propeller may not be part of the propeller type design. These components have typically been hydraulic controls, electronic controls, overspeed governors, spinners, de-icing boots, and de-icing components. When components are not included in the propeller type design, they are not under the design control of the propeller TC holder, but instead, are controlled by the aircraft or engine TC holders. Even though these components are not within the scope of the propeller type design, compliance with some part 35 regulations requires that representative or typical components be included and, to some extent, evaluated during the design and testing phases of propeller certification.

2.1.4 Components Substantiated for Use with the Propeller (Accessories).

These components are typically governors, pitch control units, de-icing equipment, spinners and other accessories that are substantiated by the applicant to operate with the propeller system. They may or may not be included in the propeller type design. These components may be referenced on the propeller TCDS notes. When not included in the propeller type design, design control of these components resides with the engine or airplane TC holder. A reference in Note 10 is included on the TCDS to ensure that the

2-2 propeller installation with these components is approved during airplane certification and that it complies with applicable airplane airworthiness requirements. A reference format for a propeller TCDS is listed in Order 8110.4, along with the statement to be included in Note 10.

2.1.5 De-icing Equipment.

Propeller type certification does not verify compliance with 14 CFR part 23 or 14 CFR part 25 airplane requirements to show that the de-icing equipment will provide acceptable ice protection performance on the airplane. Airplane icing capability is demonstrated on the airplane in accordance with applicable airplane airworthiness requirements. The deicing system on the propeller is required to meet the applicable structural and durability requirements of 14 CFR part 35.

2.1.6 Contra-rotating Propellers.

Title 14 CFR part 35 was written for a single rotation tractor propeller configuration.

The complexity of a contra-rotating propeller has not been considered; therefore, additional requirements may need to be established.

2.1.7 Pusher Propellers.

Additional aircraft installation design and test factors may be needed for a pusher propeller configuration that is not included in part 35, such as engine exhaust heat and aircraft ice shedding. These factors may be incorporated into § 35.19 requirement as agreed to by the Administrator.

2.2 Section 35.2, Propeller configuration.

Applicants must provide a parts list of all components in the propeller type design.

The list of components does not need to be reduced to a piece part level. Component assemblies, such as blades or controls, may be listed by assembly part number with references to the appropriate drawings.

2.3 Section 35.3, Instructions for propeller installation and operation.

The instructions for propeller installation and operation in the installation manual may apply to a specific propeller model or to a family of propellers. Information on the propeller TCDS does not need to be repeated in the installation manual. The constant speed, feathering, and reversing propeller installation manual contains the following items, if applicable:

 Propeller system description.

 Propeller specifications and limitations list, such as diameter; number of blades;

power and revolutions per minute (rpm) limits; torque limits; overspeed and overtorque limits; propeller shaft loads; propeller system mounting instructions and bolt torques; propeller balance (as delivered); vibration environment; altitude versus ambient temperature limitations; ground de-icing limitations; propeller system component weights; moments of inertia; center of gravity; and list weights.

2-3  A brief control system description that may reference a more detailed system description. The description should include control system characteristics and define operation in primary and all alternate operational modes. If applicants anticipate any changes in operating characteristics when transitioning between modes or in backup mode(s), then they should describe those characteristics.

 Components and accessories list.

 Interface and rigging requirements.

 Pitch change information, such as settings; slew rates; beta sensor position; limits on intended movement below the in-flight low pitch position; feathering limitations;

and start lock engagement and disengagement rpm.

 Recommended operating procedures, such as ground (starting, propeller brake, overspeed governor check; secondary low pitch stop check; limitations and restrictions); de-icing; flight; emergency (loss of hydraulic pressure and electrical power); fault detection; isolation; and accommodation.

 Ice protection system description.

 Electrical system description, such as power requirements and loss of aircraft electrical power effects.

 Electromagnetic interface (EMI) and lightning protection information, such as system description; qualification results; and limitations.

 Actuation and lubrication system information, such as actuating and lubrication fluids; propeller pump fluid requirements; fluid filtration; lubricating fluid; hub lubricating fluid; auxiliary motor and pump; and hydraulic system pressure requirements.

 Assumptions, such as safety analysis, design, and operation.

 Propeller TCDS and supplemental type certificate references.

2.4 Section 35.4, Instructions for Continued Airworthiness.

See AC 35.4-1 for additional guidance on preparing the instructions for continued airworthiness (ICA) for propellers.

2.5 Section 35.5, Propeller ratings and operating limitations.

The rated power, rotational speed, and torque are those values declared by the applicant and substantiated to meet the requirements of part 35. The applicant may elect to conduct certification tests, analysis, and evaluation at values greater than the declared rated values. The regulations do not require that takeoff power and rpm be greater than maximum continuous power and rpm. Propeller takeoff power and rpm and maximum continuous power and rpm are validated during the endurance test required by § 35.39.

2.5.1 Power and RPM Ratings.

The power and rpm ratings declared on the propeller TCDS, do not apply to any given airplane installation. They only apply to the propeller. The propeller may have

2-4 multiple ratings, depending on the specific configuration definition that may only be suitable for operation on some aircraft at a lower power or rpm. Appropriate aircraft installation limitations are established by 14 CFR part 23 for normal category or 14 CFR part 25 for transport category aircraft. Installation limitations are also referenced in the aircraft TCDS and aircraft flight manual. The propeller power and rpm listed in the aircraft TCDS and aircraft flight manual cannot be greater than that listed on the propeller TCDS.

2.5.2 Overspeed and Overtorque Limits.

The overspeed and overtorque limits established in § 35.41 are independent of the maximum power and rotational speeds. These limits are not intended to be used routinely. They are to be used for service checks, and unplanned exceedance of torque and speed.

2.6 Section 35.7, Features and characteristics.

Applicants should review the development and service history of earlier model propellers to meet the requirements of § 35.7. For a new model, applicants should review the development and service experience of models with similar design features.

3-1 3 GUIDANCE FOR SUBPART B – DESIGN AND CONSTRUCTION

3.1 Section 35.15, Safety analysis.

3.1.1 Safety Analysis Objective.

The safety analysis objective is to ensure the risk to the aircraft from all propeller failure conditions is within an acceptable range. An acceptable total propeller design risk is achievable by managing the individual, major, and hazardous risks to acceptable levels. This concept emphasizes reducing the risk of the likelihood or probability of an event in proportion to the severity of the hazard event occurrence. Safety analysis results should support the regulatory compliance goals so that major or hazardous propeller effects do not exceed an established probability of occurrence.

3.1.1.1 Safety Assessment Scope. The depth and scope of an acceptable safety assessment depends on the complexity and criticality of the functions performed by the system(s), components, or assemblies under consideration. Severity of related failure conditions, design uniqueness, relevant service experience, number and complexity of the identified causal failure scenarios, and the ability to detect contributing failures are also included.

3.1.1.2 Safety Analysis Methods. There are various safety analysis methods for assessing the causes, severity levels, and likelihood of potential failures available to support experienced engineering judgment. Some common safety analysis methods, based on inductive or deductive approaches, include FTA, FMEA, or dependence diagram (reliability block diagram), Markov analysis, or preliminary system safety assessment. See paragraph

3.1.10 for further discussion.

3.1.2 Propeller Level Failure Conditions.

Part 35 certification procedures address a single propeller. Therefore, the effects of failures should be assessed at the propeller level, independent of the airplane installation. When the propeller passes into the certification environment of the airplane, specifics of the particular installation are used to address the issues of power plant redundancy or the effects of various failure conditions to the airplane. The FAA ACO Branch and the FAA standard branches regulate the airplane-level effects of all parts of the airplane, including propellers.

3.1.2.1 Propeller Failure Classifications. Airplane failure classifications do not apply directly to propeller failure classifications. The airplane may have features that decrease or increase the consequences of a propeller failure effect. Additionally, the same type of certificated propellers may be used in a variety of installations, each with different airplane failure classifications. Therefore, in the absence of an actual safety classification from aircraft and engine manufacturers, the classification of the