AC 23-24

AIRWORTHINESS COMPLIANCE CHECKLISTS 

FOR COMMON PART 23 SUPPLEMENTAL TYPE 

CERTIFICATE (STC) PROJECTS 

August 24, 2005 

For sale by the Superintendent of Documents, U.S. Government Printing Office, Initiated By: ACE-100 

Washington DC 20401 

8/24/05 AC 23-

24T 

FOREWORD 

This Advisory Circular (AC) describes one method that may be used to generate compliance 

checklists for some common airplane changes. These compliance checklists may be used to 

fulfill some of the requirements for a Certification Plan as part of a part 23 STC project. 

s/ Kim Smith 

Acting Manager, Small Airplane Directorate 

Aircraft Certification Service 

i (and ii) 

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CONTENTS

Section Page

1. What is the purpose of this Advisory Circular (AC)?..............................................................1 

2. Who is affected by this AC? ....................................................................................................1 

3. What documents does this AC supersede? ..............................................................................1 

4. What other publications are related to this AC? ......................................................................1 

5. How is this Advisory Circular (AC) related to other Federal Aviation 

Administration (FAA) ACs and Policy Statements? .......................................................................5 

6. What common STC projects does this AC address? ...............................................................6 

7. Where can the common STC project checklists be found? .....................................................7 

8. How were the standard compliance checklist and the lists of

applicable regulations for these common STC projects developed? ...............................................7 

9. How should the compliance checklists in this AC be used in 

certification projects?.......................................................................................................................7 

10. Should these checklists be combined into one for projects that cover 

more than one of these changes? .....................................................................................................7 

11. How should the standard checklist be filled in to generate a checklist 

specific to a project? ........................................................................................................................8 

12. What are the applicable regulations and guidance for the installation 

of an autopilot system? ..................................................................................................................14 

13. What are the applicable regulations and guidance for the installation 

of a reciprocating engine with increased horsepower? ..................................................................15 

14. What are the applicable regulations and guidance for the installation 

of a turbo-prop engine with increased horsepower? ......................................................................17 

15. What are the applicable regulations and guidance for the installation 

of turbine engines to replace reciprocating engines?.....................................................................20 

16. What are the applicable regulations and guidance for the installation 

of a different propeller (simple)? ...................................................................................................21 

17. What are the applicable regulations and guidance for the installation 

of a different propeller (complex)? ................................................................................................22 

18. What are the applicable regulations and guidance for the installation 

of auxiliary fuel tanks?...................................................................................................................23 

19. What are the applicable regulations and guidance to increase the 

airplane gross weight?....................................................................................................................23 

APPENDIX 1 – Standard Compliance Checklist..................................................................... A1-1 

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FIGURES 

Figure Page

Figure 1 – First page of the compliance checklist ........................................................................ 11 

Figure 2 – Second page of the compliance checklist.................................................................... 12 

Figure 3 – Example of an expanded checklist entry..................................................................... 13 

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AIRWORTHINESS COMPLIANCE CHECKLISTS FOR COMMON PART 23 

SUPPLEMENTAL TYPE CERTIFICATE (STC) PROJECTS 

1. What is the purpose of this Advisory Circular (AC)? 

This AC provides information to create compliance checklists for some common Title 14 of the 

Code of Federal Regulations (14 CFR) part 23 Supplemental Type Certificate (STC) projects. 

These checklists may be used to fulfill some of the requirements for a Certification Plan for STC 

projects. The standard compliance checklist provided with this AC shows typical methods of 

compliance with the regulations and provides a cross-reference to other related guidance 

material. Guidance specific to STCs for autopilot, engine, propeller, auxiliary fuel tank, and 

gross weight changes is included in sections 12 through 19 of this AC. The checklists created 

using the information in this AC complement the guidance in the Guides for Certification of Part 

23 Airplanes (ACs 23-8B, 23-16A, 23-17B, and 23-19) and other more project-specific 

guidance. The certification requirements listed in sections 12 through 19 of this AC may be 

complete for certain STC projects or may be used as a starting place when applying for an STC 

that may be beyond the scope of the common STCs in this AC. This AC describes an acceptable 

means, but not the only means, of compliance with 14 CFR part 23. The material in this AC is 

neither mandatory nor regulatory in nature and does not constitute a regulation. 

2. Who is affected by this AC? 

a. Anyone applying for an STC for the common changes covered in this AC may create a 

project-specific compliance checklist as a starting point for discussions with their geographical 

Aircraft Certification Office (ACO). The list of ACOs with their addresses and phone numbers 

may be found on the Internet at www.faa.gov/certification/aircraft/acochart.htm. 

b. Federal Aviation Administration (FAA) engineers working on STC projects for the 

common changes covered in this AC may also use the compliance checklists created using this 

AC as a basis for discussions with anyone applying for an STC. 

3. What documents does this AC supersede? 

This AC does not supersede any existing documents. 

4. What other publications are related to this AC? 

The publications listed in these paragraphs are a representative selection of documents that are 

relevant to part 23 airplane certification. The compliance checklist in Appendix 1 references 

many of these publications as guidance applicable to individual regulations. Depending on the 

details of a particular certification project, other guidance material may apply, and the project 

specific checklist should include all guidance material used. A complete list of documents is 

available at the Internet addresses listed below. 

a. Regulations: 

In general, this AC covers 14 CFR part 23 regulations in their entirety. Specific regulations that 

are applicable to the common STC projects covered in this AC are listed in paragraphs 12 

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through 19. In addition, the following regulations are available on the Internet at 

www.airweb.faa.gov/far. 

14 CFR part 21, subpart E Supplemental Type Certificates 

14 CFR part 33 Airworthiness Standards: Aircraft Engines 

14 CFR part 34 Fuel Venting and Exhaust Emission Requirements for Turbine 

Engine Powered Airplanes 

14 CFR part 35 Airworthiness Standards: Propellers 

14 CFR part 36 Noise Standards: Aircraft Type and Airworthiness 

Certification

Many small airplanes certificated before the Civil Air Regulations (CARs) recodification to the 

Federal Aviation Regulations in 1964 list the CARs in their original certification basis. The 

checklist in Appendix 1 lists the CAR 3 cross-reference to the 14 CFR part 23 regulations at the 

recodification. These historic references are on the Internet at 

http://dotlibrary.specialcollection.net/. 

b. FAA Orders and ACs available at no charge: 

Copies of the current FAA orders and ACs listed below may be obtained at no charge from: 

U.S. Department of Transportation 

Subsequent Distribution Office, M-30 

Ardmore East Business Center 

3341Q 75th Avenue 

Landover, MD 20795 

Telephone: 301-322-4779 

Facsimile: 301-386-5394 

These documents are also available on the Internet at www.airweb.faa.gov/orders and 

www.airweb.faa.gov/ac respectively.

FAA Order 8110.4B Type Certification 

FAA Order 8110.48 How to Establish a Certification Basis for Changed 

Aeronautical Products 

AC 20-53A Protection of Aircraft Fuel Systems Against Fuel Vapor 

Ignition Due to Lightning 

AC 20-66A Vibration and Fatigue Evaluation of Airplane Propellers 

AC 20-73 Aircraft Ice Protection 

AC 20-74 Aircraft Position and Anticollision Light Measurements 

AC 20-88A Guidelines on the Marking of Aircraft 

AC 20-119 Fuel Drain Valves 

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AC 20-122A Anti-misfueling Devices: Their Availability and Use 

AC 20-124 Water Ingestion Testing for Turbine Powered Airplanes 

AC 20-128A Design Consideration for Minimizing Hazards Caused by 

Uncontained Turbine Engine and Auxiliary Power Unit Rotor 

Failure

AC 20-130A Airworthiness Approval of Navigation or Flight Management 

Systems Integrating Multiple Navigation Sensors 

AC 20-135 Powerplant Installation and Propulsion System Component 

Fire Protection Test Methods, Standards, and Criteria 

AC 20-136 Protection of Aircraft Electrical/Electronic Systems against the 

Indirect Effects of Lightning 

AC 20-138A Airworthiness Approval of Global Navigation Satellite System 

(GNSS) Equipment 

AC 20-146 Methodology for Dynamic Seat Certification by Analysis for 

Use in Part 23, 25, 27, and 29 Airplanes and Rotorcraft 

AC 20-147 Turbojet, Turboprop, and Turbofan Engine Induction System

Icing and Ice Ingestion 

AC 21-40 Application Guide for Obtaining a Supplemental Type 

Certificate 

AC 21.101-1 CHG 1 Establishing the Certification Basis of Changed Aeronautical 

Products 

AC 23-2 Flammability Tests 

AC 23-9 [Large AC] Evaluation of Flight Loads on Small Airplanes 

with T, V, +, or Y Empennage Configurations 

AC 23-10 Auxiliary Systems for Reciprocating and Turbine Powered part 

23 Airplanes 

AC 23-13 Fatigue and Fail-Safe Evaluation of Flight Structure and 

Pressurized Cabin for Part 23 Airplanes 

AC 23-14 Type Certification Basis for Conversion from Reciprocating 

Engine to Turbine Engine-Powered Part 23 Airplanes 

AC 23-15A Small Airplane Certification Compliance Program 

AC 23-15A CHG 1 Small Airplane Certification Compliance Program 

AC 23-19 Airframe Guide for Certification of Part 23 Airplanes 

AC 23-21 Airworthiness Compliance Checklists Used to Substantiate 

Major Alterations for Small Airplanes 

AC 23-21 CHG 1 Airworthiness Compliance Checklists Used to Substantiate 

Major Alterations for Small Airplanes 

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AC 23-23 Standardization Guide for Integrated Cockpits in Part 23 

Airplanes 

AC 23.143-1 Ice Contaminated Tailplane Stall (ICTS) 

AC 23.562-1 Dynamic Testing of Part 23 Airplane Seat/Restraint Systems 

and Occupant Protection 

AC 23.607-1 Self-Locking Nuts on Bolts Subject to Rotation 

AC 23.629-1B Means of Compliance with Section 23.629 “Flutter” 

AC 23.1309-1C Equipment, Systems, and Installations in Part 23 Airplanes 

AC 23-1311-1A Installation of Electronic Displays in Part 23 Airplanes 

AC 23.1419-2C Certification of Part 23 Airplanes for Flight in Icing Conditions 

AC 23-1523 Minimum Flight Crew 

AC 33-2B Aircraft Engine Type Certification Handbook 

AC 33.28-1 Compliance Criteria for 14 CFR § 33.28, Aircraft Engines, 

Electrical and Electronic Engine Control Systems 

AC 33.28-2 Guidance Material for 14 CFR § 33.28, Reciprocating Engines, 

Electrical and Electronic Engine Control Systems 

AC 35.37-1A Composite Propeller Blade Fatigue Substantiation 

AC 36-1H Noise Levels for U.S. Certificated and Foreign Aircraft 

AC 36-2C Measured or Estimated (Uncertificated) Airplane Noise Levels 

AC 36-3H Estimated Airplane Noise Levels in A-Weighted Decibels 

AC 36-4C Noise Standards: Aircraft Type and Airworthiness 

Certification

AC 183.29-1HH Designated Engineering Representatives 

c. ACs available for purchase: 

Copies of the current ACs listed below are available to buy from: 

Superintendent of Documents 

P.O. Box 371954 

Pittsburgh, PA 15250-7954 

These documents are also available on the Internet at www.airweb.faa.gov/ac. 

AC 23-8B Flight Test Guide for Certification of Part 23 Airplanes 

AC 23-16A Powerplant Guide for Certification of Part 23 Airplanes and 

Airships 

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AC 23-17B Systems and Equipment Guide for Certification of Part 23 

Airplanes and Airships 

AC 23-19 Airframe Guide for Certification of Part 23 Airplanes 

d. Policy Statements: 

Copies of the current Policy Statements listed below may be obtained at no charge from:

Small Airplane Directorate Regulations and Policy Branch 

901 Locust St., Room 301 

Kansas City, MO 64106 

These documents are also available on the Internet at www.airweb.faa.gov/policy. 

PS-ACE100-2001-004 Guidance for Reviewing Certification Plans to Address Human 

Factors for Certification of Part 23 Small Airplanes 

PS-ACE100-2001-006 Static Strength Substantiation of Composite Airplane Structure 

PS-ACE100-2002-002 Installation Approval of Multi-Function Displays Using the 

AML STC Process 

PS-ACE100-2002-004 Diesel Engine Installations 

PS-ACE100-2002-006 Material Qualification and Equivalency for Polymer Matrix 

Composite material Systems 

PS-ACE100-2002-007 Final Policy for Pitot Heat Indication Systems for 14 CFR, Part 

23, § 23.1326(b)(1) 

PS-ACE100-2002-008 Propeller Testing Vd Versus VNE 

PS-ACE100-2004-10023 Final Policy Statement for Flammability of Electrical Wiring 

Used in Part 23 Aircraft per 14 CFR, part 23, §§ 23.853 and 

23.1359 

PS-ACE100-2004-10024 Installation of Electronic Engine Control for Reciprocating 

Engine 

PS-ACE100-2004-10030 Substantiation of Secondary Composite Structures 

5. How is this Advisory Circular (AC) related to other Federal Aviation Administration 

(FAA) ACs and Policy Statements? 

a. This AC provides guidance on the applicable sets of regulations for some common STC 

projects and a standard checklist to use in creating a project-specific checklist. The standard 

checklist shows the typical methods of compliance with the regulations and cross-references 

other related guidance material. This AC is organized by topic to address some common STC 

projects and is to be used with other published guidance described in b and c below. 

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b. The Small Airplane Directorate has published Guides for Certification of Part 23 

Airplanes covering broad sections of Title 14 of the Code of Federal Regulations (14 CFR) part 

23 regulations (that is: Flight Test, Powerplant, Systems, and Structures). These Guides for 

Certification of Part 23 Airplanes (that is: ACs 23-8B, 23-16A, 23-17B, and 23-19) provide 

guidance for showing compliance with individual regulations. 

c. The Small Airplane Directorate has published ACs and Policy Statements that address 

specific airplane installations (for example: AC 23-10, AC 23-14, and AC 23-1419-2C). These 

documents provide guidance for showing compliance with the sets of regulations applicable to 

specific airplane design changes and installations. 

6. What common STC projects does this AC address? 

a. Review of databases for STCs and Certification Project Notices (CPNs) initiated since 

2002 shows the five most common categories of changes over this time period are: 

(1) Automatic Flight Control Systems installations, including autopilot installations with 

electric trim; 

(2) Engine installations, including total engine replacements, horsepower (hp) increases, 

using different engine mounts, adding Full Authority Digital Engine Controls (FADEC), cowling 

modifications, and adding turbochargers; 

(3) Propeller installations, including spinner changes and new propellers with different 

diameters, different number of blades, and variable pitch; 

(4) Fuel systems installations, including the addition of auxiliary fuel tanks/cells, fuel 

filters and flow transducers, annunciators, indicators and pumps, and adding tip tanks; and 

(5) Airplane gross weight increases. 

b. These categories encompass many different potential airplane changes. This AC covers 

the following specific STC projects. In the future, checklists may be added to this AC to cover 

other specific STC projects. 

(1) Installation of an autopilot system; 

(2) Installation of a reciprocating engine with increased horsepower; 

(3) Installation of a turbine engine with increased horsepower; 

(4) Installation of turbine engines to replace reciprocating engines; 

(5) Installation of a different propeller (simple); 

(6) Installation of a different propeller (complex); 

(7) Installation of auxiliary fuel tanks; and 

(8) Increase in the airplane gross weight. 

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7. Where can the common STC project checklists be found? 

A standard checklist is in Appendix 1. Sections 12 through 19 of this AC list the basic 

regulations applicable to each of the different common STC projects. This information may be 

used to create a checklist for the project as described in sections 9, 10, and 11. The checklists 

created using this AC are also available on the Internet at 

http://www.faa.gov/other_visit/aviation_industry/designees_delegations/tools/forms/checklists in 

a format that allows the user to fill the forms in on their computer. 

8. How were the standard compliance checklist and the lists of applicable regulations for 

these common STC projects developed? 

Checklists used by various ACOs on past and present certification projects and current guidance 

material were used to develop the standard compliance checklist and the lists of applicable 

regulations for each of the common STC projects.

9. How should the compliance checklists in this AC be used in certification projects? 

Order 8110.4B and AC 21-40 describe the STC application process that begins with the 

applicant submitting a completed FAA Form 8110-12 with a Certification Plan. A compliance 

checklist may fulfill some of the requirements for the Certification Plan. The information in this 

AC is a starting point to create a project-specific compliance checklist for some common STC 

projects that tells how the applicant intends to show compliance with the regulations. This 

checklist submitted as part of the Certification Plan provides applicants and ACO engineers a 

communication tool to begin the project. 

10. Should these checklists be combined into one for projects that cover more than one of 

these changes? 

Yes, the requirements for each of the changes should be combined into a single checklist if the 

project includes more than one of the changes listed in this AC. For example, adding auxiliary 

fuel tanks could involve a gross weight increase. In such cases, it is prudent to plan the 

certification program to show compliance to the applicable rules for these changes at the same

time. 

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11. How should the standard checklist be filled in to generate a checklist specific to a 

project? 

Figures 1 and 2 show the first and second pages of the standard compliance checklist from 

appendix 1 of this AC. The following paragraphs describe the checklist entries with the letters of

the paragraphs below matching the circled letters in the figures. A template checklist for each of 

the common STC projects listed in sections 12 through 19 of this document is available at 

http://www.faa.gov/other_visit/aviation_industry/designees_delegations/tools/forms/checklists. 

The regulations shown in the standard and template checklists do not show all subparagraphs. 

Where the method of compliance differs between subparagraphs of the same regulation, you 

should expand the checklist to show the subparagraphs and the methods of compliance for each. 

Figure 3 shows an example of an expanded checklist entry. 

a. When you initially use the checklist, this field will be blank. The ACO assigns a project 

number when accepting the project application. 

b. Enter the name of the originator of the completed checklist. 

c. Enter the date of the latest checklist revision. 

d. Enter the latest checklist revision. The applicant may choose any method to track this, 

provided it can distinguish different versions. For example, use sequential numbering or 

lettering for each new version of the checklist. 

e. Enter the make of the airplane to receive this STC, as shown on the Type Certificate Data 

Sheet (TCDS) (for example: Cessna, Piper). 

f. Enter the complete model number of the airplane to receive this STC, as shown on the 

TCDS (for example: 150C, PA-32-260). 

g. Enter the number of the TCDS for the airplane make and model listed in e and f. The 

TCDS information is on the Internet at www.airweb.faa.gov/TCDS. 

h. Enter the original certification basis of the airplane as listed on the airplane TCDS. It is 

acceptable to reference the airplane TCDS. 

i. Enter the proposed certification basis for this STC project. Refer to AC 21.101-1 CHG 1 

and FAA Order 8110.4B for guidance on choosing the proposed certification basis. 

j. Check the box to indicate whether the proposed STC is for one serial number only or if it 

will be for duplication on other aircraft. 

k. Enter a brief description of the modification similar to that stated on FAA Form 8110-12 

(found in FAA Order 8110.4B). A complete description of the change will appear in the 

certification plan provided to the ACO as described in FAA Order 8110.4B. 

l. Enter the page number and the number of pages. 

m. Enter the applicable regulation amendment level used as the Certification Basis for the 

STC. 

n. Enter the method or combination of methods used to show compliance with the 

regulations. Make an entry for each regulation (or sub-paragraph as explained in paragraph 11 

above) in the checklist. The regulations listed in sections 12 through 19 are considered the 

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minimum required for showing compliance. Other regulations may be applicable depending on 

the specific changes proposed for the STC. Determine the applicability to the project for all the 

regulations. The standard checklist in appendix 1 lists typical methods of compliance that have 

been acceptable for other STC projects in the past. The unique features of the project may 

require other combinations of methods. Check whether the methods listed are appropriate and 

change them to reflect the certification plan for the specific STC project. When choosing the 

applicable regulations, make sure to consider the impact of the airplane changes on areas such as 

structural integrity, performance, controllability, and human factors. See FAA Policy Statement 

PS-ACE100-2001-004 for guidance that addresses human factors considerations. Use the 

following definitions when filling in this column. A more detailed description of the method of 

compliance (for example: component testing, hand calculations, validated finite element model 

analysis, or a combination of methods) should be included in any compliance plans referenced in 

the checklist plan column and remarks column described in sections 11.o and 11.q respectively. 

(1) Flight Test (FT) – This method of compliance is a test of the airplane in the air or on 

the ground when the nature of the test requires a flight test pilot. 

(2) Ground Test (GT) – This method of compliance includes component bench testing, 

testing of simulated airplane systems, and ground testing of the airplane. These tests may be 

precursors to a flight test or may be used to show compliance when appropriate, and judged to be 

conservative. 

(3) Analysis (AN) – This method of compliance includes a quantitative or qualitative 

assessment, as appropriate, of structures, systems, components, or the entire airplane. An 

analysis may be a precursor to ground and flight tests and a validation of the design. An analysis 

must be validated using published previous experience or appropriate testing to be accepted for 

showing compliance to the regulations. 

(4) Design (DE) – This method of compliance encompasses the inherent features of 

structures, systems, or components. Inspection of airplane hardware, the drawings, the bill of 

materials, or other documentation, such as material specifications shows compliance with the 

applicable regulations. 

(5) Similarity (SI) – This method of compliance is a comparison between a previously 

certificated design and the proposed design. The intent is to show that these designs are the same

in all ways relative to showing compliance with the applicable regulation, so the proposed design 

will perform the same or better than the previously certificated design. The applicant must 

account for any differences in the regulations if the amendment levels of the regulations are not 

the same for the two designs. Refer to the other guidance applicable to the different regulations 

to determine if similarity is proper. 

(6) Equivalent Level of Safety Finding (ELOS) – Title 14 CFR part 21, § 21.21(b)(1) and 

FAA Order 8110.4B paragraph 2-10g describe this method of compliance. An ELOS is issued 

when the applicant cannot show literal compliance with a regulation, and the applicant shows to 

the FAAs satisfaction that compensating factors achieve a safety level equal to that of the 

applicable regulation. The applicant may propose the use of an ELOS by submitting a letter to 

the ACO for consideration. The FAA is responsible for making the finding of equivalency and 

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issuing the ELOS memo if satisfied. If proposing an ELOS for a given regulation, enter the 

reference for the proposal letter into the checklist under the “Plan, Drawing, Report Number” 

column for the regulation (see section 11.o.) and on the last page of the checklist under the 

“EQUIVALENT LEVELS OF SAFETY (ELOS):” heading. Make all proposals for ELOSs to 

the ACO early in the project to allow time for processing. 

(7) Petition for Exemption (PExmpt) – Title 14 CFR part 11, § 11.15 defines a petition 

for exemption as, “...a request to the FAA by an individual or entity asking for relief from the 

requirements of a current regulation.” Petitions for exemptions are rulemaking as described in 

14 CFR part 11 and are subject to a public review process that is outside the scope of this AC. If 

petitioning for exemption from a given regulation, enter the reference for the petition letter into 

the “Plan, Drawing, Report Number” column for the regulation (see section 11.o.) and on the last 

page of the checklist under the “EXEMPTIONS:” heading. Make all petitions for exemption to 

the ACO early in the project to allow time for processing. 

(8) Not Applicable (N/A) – This means the specific regulation does not apply to the 

design or modification for this STC; therefore, a showing of compliance is not necessary. Enter 

the reason the rule is not applicable in the “Applicable Guidance, References, and Remarks” 

column of the checklist described in section 11.q. below. 

o. Enter the plan, drawing, and report numbers used to document the showing of 

compliance with the regulation. The items referenced here should contain sufficient detail to 

show compliance to the regulation. 

p. Enter the name and designee number (as applicable) of the Person or Entity that will find 

or recommend compliance with each of the applicable regulations. This could be a Designee 

(Designated Engineering Representatives (DER), Designated Alteration Stations (DAS), 

Delegated Option Authorization) or the FAA. The FAA encourages applicants to use Designees 

in their projects. More information on designees is on the Internet at 

www.faa.gov/other_visit/aviation_industry/designees_delegations. Consultant DERs typically 

provide their services to applicants for a fee. A directory of DERs is available in 

AC 183.29-1HH. An updated electronic directory and more information on DERs may is on the 

Internet at www.faa.gov/certification/aircraft/av-info/dst/DER_content.htm. Get Designees 

concurrence before submitting the checklist to the ACO. 

q. Enter the applicable guidance followed as well as other references and remarks clarifying 

how you are showing compliance with the applicable regulations. If entering N/A for Method of 

Compliance, enter the reason the rule is not applicable in this column. The checklist in this AC 

lists the latest revisions of other ACs with applicable guidance in this column. These revisions 

are current as of the release date of AC 23-24. When creating a project-specific checklist, enter 

the latest revisions of these documents in this column as found on the Internet at 

www.airweb.faa.gov/AC. Reference other applicable guidance as appropriate. 

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a 

g

f 

e 

b d

c 

j

k

h 

i 

l

 Figure 1 – First page of the compliance checklist 

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b

a 

d

c 

m n o p q

l

 Figure 2 – Second page of the compliance checklist 

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 Figure 3 – Example of an expanded checklist entry

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12. What are the applicable regulations and guidance for the installation of an autopilot 

system? 

a. This change covers the installation of components associated with an autopilot system

including the autopilot mode control and annunciation panel, the autopilot computer, the servos 

and actuators that drive control surfaces, and the data sources (pressure sensors, attitude data 

sources, navigation sources, other system interfaces) needed for proper functioning. The 

certification requirements for these installations are dependent on the type of autopilot system

being implemented. AC 23-17B provides additional guidance regarding autopilot installations. 

b. There are common certification issues that are related to autopilot installation approvals 

that need to be addressed, but are not covered in AC 23-17B and other existing guidance. Most 

of these issues can be related to specific installation aspects and complexity of a particular 

installation, the interface with existing systems on a particular airplane, and maintenance related 

issues. These items are dependent on the autopilot design. The following are examples of items

that should be considered: 

(1) Certification Basis: Advisory Circular 21.101-1 CHG 1 generally classifies autopilot 

installations as non-significant. Digital autopilot systems frequently are complex enough that 

this may not be the case. These systems may require additional effort to assure the proper 

interactions of the software and hardware. Hardware design assurance should also include 

RTCA/DO-160 testing to make sure the sensors and components being used meet appropriate 

airworthiness requirements. Other regulations in addition to those listed in section 12.c. below 

may need to be considered in this case. 

(2) System Integration: Current guidance in AC 20-130A and AC 20-138A requires the 

source of navigation information be annunciated on or near the affected display. For an autopilot 

installation, the source of navigation data must be clearly annunciated to indicate to the pilot 

which source is driving the autopilot. This could include a Global Positioning System (GPS) roll 

steering source, an Instrument Landing System course deviation source, or some other navigation 

source. The lack of clear annunciation and the subsequent potential for confusion has been a 

contributing factor to several small airplane accidents. Any new autopilot installation must be 

integrated with existing navigation systems in a way that is clear to the pilot. The autopilot 

should be designed to avoid inadvertent mode changes. Also, if a Control Wheel Steering 

(CWS) function is implemented to allow temporary interrupt of the autopilot for the pilot to 

reposition the airplane, the CWS switch should not cause inadvertent mode changes. 

(3) AFM Limitations on the Autopilot Envelope: Many autopilots are not capable of 

acceptable control of the airplane in all flight conditions. Frequently, flight manual limitations 

are used to restrict the use of the autopilot above or below a given airspeed, in certain turbulence 

conditions, or in certain airplane configurations. Title 14 CFR part 23, § 23.1329 clearly states 

that the autopilot cannot cause deviations in flight path. This includes the requirement that the 

autopilot should not be able to drive the airplane into a stalled condition, particularly in icing 

conditions. 

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(4) Maintenance Related Issues: The applicant should provide a means to insure proper 

autopilot rigging with the existing controls system. This would include checking primary and 

bridal cable tensions to make sure the airplane is rigged properly before and after the installation, 

and at regular maintenance intervals. 

c. The applicable regulations for the installation of an autopilot system should include but 

are not limited to the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.143, 23.253; 

(2) Title 14 CFR part 23, subpart C, §§ 23.301, 23.303, 23.305, 23.307, 23.391, 23.395, 

23.397, 23.561; 

(3) Title 14 CFR part 23, subpart D, §§ 23.603, 23.605, 23.607, 23.609, 23.611, 23.613, 

23.619, 23.625, 23.627, 23.671, 23.672, 23.677, 23.685, 23.689, 23.693, 23.771, 23.777, 23.779, 

23.853, 23.867; 

(4) Title 14 CFR part 23, subpart F, §§ 23.1301, 23.1307, 23.1309, 23.1311, 23.1321, 

23.1322, 23.1325, 23.1329, 23.1335, 23.1351, 23.1357, 23.1359, 23.1365, 23.1367, 23.1381, 

23.1431; and 

(5) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1529, 23.1541, 23.1555, 23.1581, 

23.1583, 23.1585. 

13. What are the applicable regulations and guidance for the installation of a reciprocating 

engine with increased horsepower? 

a. This change covers the replacement of a spark ignition reciprocating engine with a 

different spark ignition reciprocating engine that is able to supply more horsepower. This type of 

change is done mostly to increase the performance of the airplane in take-off and climb and 

maintains the airspeed limits of the airplane. These installations may increase the gross weight 

of the airplane in which case the applicant should refer to the gross weight increase compliance 

checklist for additional requirements. The impact of the increased horsepower on the noise level 

should be considered and accounted for per Title 14 CFR part 36. AC 23-19 provides additional 

guidance regarding modifications involving increased engine power. 

b. The need for a limited spin matrix on an STC program is a subjective decision based on 

the service history of the specific airplane being modified. It is not possible to offer a 

comprehensive list of when to re-test the spin matrix because of the number of variables to 

consider. There are instances of airplanes with significant modifications that had little effect on 

spin recovery, and airplanes with subtle modifications that changed the spin recovery 

dramatically. If it is determined that the airplane does need to be re-evaluated for spin recovery, 

then a limited matrix using the middle and edges of the envelope is normally all that is needed to 

verify the airplane recovers. 

c. The following key airplane characteristics and features seem to relate directly to the 

“stall/spin” or departure accidents, and should indicate the need for more evaluation of the spin 

characteristics. 

15 
AC 23-24T 

8/24/05 

(1) Stall characteristics - Does the airplane just buffet at full aft control or does it roll 

off dramatically with no aerodynamic warning? Does the airplane require talented footwork to 

keep the wings level or could the pilot put their feet on the floor during the stall with little rolloff? An airplane that is resistant to stalling and easy to keep the wings level may not need a spin 

recovery re-evaluation, but an airplane with poor stall handling qualities and a poor “stall/spin” 

accident history will need a spin recovery re-evaluation. 

(2) Stick force gradient - Airplanes with steep stick force gradients are involved in 

fewer “stall/spin” accidents than airplanes with light force gradients. 

(3) Stall warning - A stall warning system can reduce the number of “stall/spin” 

accidents depending on the effectiveness of the system. There are numerous stall warning 

schemes ranging from the ineffective lights to the very effective stick shakers with warning 

horns. 

d. The following rules-of-thumb have been used with reasonable success since 1972 for 

airplane changes that increase the power and should be considered when addressing the spin 

recovery. 

(1) Spin tests that are required because of mass distribution changes will require the use 

of power (75% Maximum Continuous Power (MCP) / thrust or full throttle, whichever is less) 

for one full turn into the spin. 

(2) Airplanes modified by increasing the installed horsepower (maximum takeoff power) 

by more than 10% or 25 horsepower, whichever is less, over the original type certificated 

airplane installed horsepower rating, will require spin testing.

(3) Turbocharged engine installations will be evaluated as follows: 

(a) Determine the maximum power available on the original engine at 10,000 feet 

pressure altitude. 

(b) Determine the value of 75% MCP on the new engine. 

(c) If the difference between (a) and (b) exceeds either 10% of the original installed 

horsepower (maximum takeoff power) or 25 horsepower, spin tests will be conducted. 

(4) Airplanes modified as described in paragraph 9.d.(2) may accept a de-rated power 

schedule in lieu of spin testing. The maximum horsepower difference criteria, 10% or 25 

horsepower, whichever is less, applies from sea level to the airplane service ceiling. This 

requires a placard of manifold pressure versus pressure altitude (at rated Revolutions Per Minute 

(RPM)) corresponding to the maximum allowable horsepower differential between the de-rated 

engine and the original type certificated engine. 

16 
8/24/05 AC 23-

24T 

e. Using a limited spin matrix should be considered if the change to the airplane causes a 

weight and/or a rotational inertia increase of greater than 10%. 

f. The applicable regulations for the installation of a reciprocating engine with increased 

horsepower should include, but are not limited to, the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.25, 23.33, 23.45, 23.49, 23.65, 23.66, 23.67, 

23.75, 23.77, 23.143, 23.145, 23.147, 23.149, 23.155, 23.161, 23.171, 23.175, 23.177, 23.201, 

23.203, 23.207, 23.221 (except agricultural and twin engine airplanes), 23.231, 23.233, 23.235, 

23.237, 23.239, 23.251, 23.253; 

(2) Title 14 CFR part 23, subpart C, §§ 23.301, 23.303, 23.305, 23.307, 23.331, 23.333, 

23.335, 23.337, 23.341, 23.361, 23.363, 23.371, 23.479, 23.499, (23.572, 23.573, 23.574, 23.575 

as required or if part of original certification basis); 

(3) Title 14 CFR part 23, subpart D, §§ 23.601, 23.603, 23.607, 23.609, 23.611, 23.613, 

23.619, 23.627, 23.629, 23.735, 23.777, 23.779, 23.781, 23.831, 23.841, 23.863, 23.865, 23.867; 

(4) Title 14 CFR part 23, subpart E, §§ 23.901, 23.903, 23.905, 23.907, 23.925, 23.929, 

23.933, 23.939, 23.943, 23.951, 23.953, 23.954, 23.955, 23.959, 23.961, 23.991, 23.993, 23.994, 

23.995, 23.997, 23.1105, 23.1107, 23.1011, 23.1013, 23.1015, 23.1017, 23.1019, 23.1021, 

23.1023, 23.1027, 23.1041, 23.1043, 23.1047, 23.1091, 23.1093, 23.1101, 23.1103, 23.1105, 

23.1107, 23.1121, 23.1123, 23.1141, 23.1143, 23.1145, 23.1147, 23.1149, 23.1153, 23.1163, 

23.1165, 23.1181, 23.1182, 23.1183, 23.1189, 23.1191, 23.1193, 23.1195, 23.1197, 23.1199, 

23.1201, 23.1203; 

(5) Title 14 CFR part 23, subpart F, §§ 23.1301, 23.1303, 23.1305, 23.1309, 23.1311, 

23.1321, 23.1322, 23.1329, 23.1337, 23.1351, 23.1353, 23.1357, 23.1359, 23.1416, 23.1437, 

23.1435, 23.1438; 

(6) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1505, 23.1513, 23.1521, 23.1527, 

23.1529, 23.1541, 23.1543, 23.1545, 23.1549, 23.1551, 23.1555, 23.1557, 23.1581, 23.1583, 

23.1585, 23.1587; and 

(7) Title 14 CFR part 36. 

14. What are the applicable regulations and guidance for the installation of a turbo-prop 

engine with increased horsepower? 

a. This change covers the replacement of a turbo-prop engine with a different turbo-prop 

engine that is able to supply more horsepower. This type of change is done mostly to increase 

the performance of the airplane in take-off, climb, and cruise at altitude. These installations may 

increase the gross weight of the airplane, in which case, the applicant should refer to the gross 

weight increase compliance checklist for additional requirements. The impact of the increased 

horsepower on the noise level should be considered and accounted for per Title 14 CFR part 36. 

AC 23-19 provides additional guidance regarding modifications involving increased engine 

power. 

17 
AC 23-24T 

8/24/05 

b. The need for a limited spin matrix on an STC program is a subjective decision based on 

the service history of the specific airplane being modified. It is not possible to offer a 

comprehensive list of when to re-test the spin matrix because of the number of variables to 

consider. There are instances of airplanes with significant modifications that had little effect on 

spin recovery, and airplanes with subtle modifications that changed the spin recovery 

dramatically. If it is determined that the airplane does need to be re-evaluated for spin recovery, 

then a limited matrix using the middle and edges of the envelope is normally all that is needed to 

verify the airplane recovers. 

c. The following key airplane characteristics and features seem to relate directly to the 

“stall/spin” or departure accidents, and should indicate the need for more evaluation of the spin 

characteristics. 

(1) Stall characteristics - Does the airplane just buffet at full aft control or does it roll 

off dramatically with no aerodynamic warning? Does the airplane require talented footwork to 

keep the wings level or could the pilot put their feet on the floor during the stall with little rolloff? An airplane that is resistant to stalling and easy to keep the wings level may not need a spin 

recovery re-evaluation, but an airplane with poor stall handling qualities and a poor “stall/spin” 

accident history will need a spin recovery re-evaluation. 

(2) Stick force gradient - Airplanes with steep stick force gradients are involved in 

fewer “stall/spin” accidents than airplanes with light force gradients. 

(3) Stall warning - A stall warning system can reduce the number of “stall/spin” 

accidents depending on the effectiveness of the system. There are numerous stall warning 

schemes ranging from the ineffective lights to the very effective stick shakers with warning 

horns. 

d. The following rules-of-thumb have been used with reasonable success since 1972 for 

airplane changes that increase the power and should be considered when addressing the spin 

recovery. 

(1) Spin tests that are required because of mass distribution changes will require the use 

of power (75% MCP or full throttle, whichever is less) for one full turn into the spin. 

(2) Airplanes modified by increasing the installed horsepower (maximum takeoff power) 

by more than 10% or 25 horsepower, whichever is less, over the original type certificated 

airplane installed horsepower rating, will require spin testing.

(3) Turboprop engine installations will be evaluated as follows: 

(a) Determine the maximum power available on the original engine at 10,000 feet 

pressure altitude. 

(b) Determine the value of 75% MCP on the new engine. 

(c) If the difference between (a) and (b) exceeds either 10% of the original installed 

horsepower (maximum takeoff power) or 25 horsepower, spin tests will be conducted. 

(4) Airplanes modified as described in paragraph 10.d.(2) may accept a de-rated power 

schedule in lieu of spin testing. The maximum horsepower difference criteria, 10% or 25 

18 
8/24/05 AC 23-

24T 

horsepower whichever is less, applies from sea level to the airplane service ceiling. This 

requires a placard of manifold pressure versus pressure altitude (at rated RPM) corresponding to 

the maximum allowable horsepower differential between the de-rated engine and the original 

type certificated engine.

e. Using a limited spin matrix should be considered if the change to the airplane causes a 

weight and/or a rotational inertia increase of greater than 10%. 

f. The applicable regulations for the installation of a turbo-prop engine with increased 

horsepower should include, but are not limited to, the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.25, 23.33, 23.45, 23.49, 23.65, 23.66, 23.67, 

23.75, 23.77, 23.143, 23.145, 23.147, 23.149, 23.155, 23.161, 23.175, 23.171, 23.177, 23.201, 

23.203, 23.207, 23.221 (except agricultural and twin engine airplanes), 23.231, 23.233, 23.235, 

23.237, 23.239, 23.251, 23.253; 

(2) Title 14 CFR part 23, subpart C, §§ 23.301, 23.303, 23.305, 23.307, 23.331, 23.333, 

23.335, 23.337, 23.341, 23.361, 23.363, 23.367, 23.371, 23.479, 23.499, (23.572, 23.573, 

23.574, 23.575 as required or if part of original certification basis); 

(3) Title 14 CFR part 23, subpart D, §§ 23.601, 23.603, 23.607, 23.609, 23.611, 23.613, 

23.619, 23.627, 23.629, 23.735, 23.777, 23.779, 23.781, 23.831, 23.841, 23.863, 23.865, 23.867; 

(4) Title 14 CFR part 23, subpart E, §§ 23.901, 23.903, 23.904, 23.905, 23.907, 23.925, 

23.929, 23.933, 23.937, 23.939, 23.943, 23.951, 23.953, 23.954, 23.955, 23.959, 23.961, 23.965, 

23.973, 23.977, 23.991, 23.993, 23.994, 23.995, 23.997, 23.1011, 23.1013, 23.1015, 23.1017, 

23.1019, 23.1021, 23.1023, 23.1027, 23.1041, 23.1043, 23.1045, 23.1091, 23.1093, 23.1103, 

23.1105, 23.1107, 23.1111, 23.1121, 23.1123, 23.1141, 23.1143, 23.1145, 23.1149, 23.1153, 

23.1155, 23.1163, 23.1165, 23.1181, 23.1182, 23.1183, 23.1189, 23.1191, 23.1193, 23.1195, 

223.1197, 23.1199, 23.1201, 23.1203; 

(5) Title 14 CFR part 23, subpart F, §§ 23.1301, 23.1303, 23.1305, (23.1307 if necessary 

to maintain original operating envelope and conditions), 23.1309, 23.1311, 23.1321, 23.1322, 

23.1329, 23.1337, 23.1351, 23.1353, 23.1357, 23.1359, 23.1416, 23.1435, 23.1437, 23.1438; 

(6) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1505, 23.1513, 23.1521, 23.1527, 

23.1529, 23.1541, 23.1543, 23.1545, 23.1549, 23.1551, 23.1555, 23.1557, 23.1581, 23.1583, 

23.1585, 23.1587; 

(7) Title 14 CFR part 34; and 

(8) Title 14 CFR part 36. 

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AC 23-24T 

8/24/05 

15. What are the applicable regulations and guidance for the installation of turbine engines 

to replace reciprocating engines? 

a. This change covers the replacement of reciprocating engines with gas turbine engines

(turbopropeller, turbojet, or turbofan). Additional guidance for this may be found in AC 23-14. 

The impact on the noise levels should be considered and accounted for per Title 14 CFR part 36. 

Installations that involve the following changes may require additional substantiation and/or 

additional certification basis requirements that could exceed the scope of this AC. 

(1) primary structure; 

(2) aerodynamics; 

(3) airspeeds; 

(4) mass distribution (may induce whirl mode, flutter, and fatigue life changes); 

(5) maximum weight; 

(6) system changes; 

(7) changes in center of gravity (c.g.) limits; or 

(8) power increases affecting high speed characteristics or airplane handling qualities. 

b. Projects such as commuter category or restricted category airplanes will require a more

detailed analysis to establish the appropriate certification basis. Installations that increase the 

gross weight of the airplane should refer to the gross weight increase compliance checklist for 

additional requirements. 

c. The applicable regulations for the installation of a turbine engine to replace a 

reciprocating engine should include, but are not limited to, the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.25, 23.33, 23.45, 23.49, 23.65, 23.67, 23.77, 

23.145, 23.149, 23.155, 23.161, 23.175, 23.177, 23.201, 23.203, 23.221 (except agricultural and 

twin engine airplanes), 23.231, 23.233, 23.239, 23.251, 23.253; 

(2) Title 14 CFR part 23, subpart C, §§ 23.301, 23.303, 23.305, 23.307, 23.331, 23.333, 

23.337, 23.341, 23.335, 23.361, 23.363, 23.367, 23.371, 23.479, (23.572, 23.573, 23.574, 23.575 

as required or if part of original certification basis); 

(3) Title 14 CFR part 23, subpart D, §§ 23.603, 23.627, 23.629, 23.735, 23.777, 23.781, 

23.831, 23.863, 23.865; 

(4) Title 14 CFR part 23, subpart E, §§ 23.901, 23.903, 23.904, 23.905, 23.907, 23.925, 

23.929, 23.933, 23.937, 23.939, 23.943, 23.951, 23.953, 23.955, 23.959, 23.961, 23.965, 23.973, 

23.977, 23.991, 23.993, 23.994, 23.995, 23.997, 23.1011, 23.1013, 23.1015, 23.1017, 23.1019, 

23.1021, 23.1023, 23.1027, 23.1041, 23.1043, 23.1045, 23.1091, 23.1093, 23.1103, 23.1111, 

23.1121, 23.1123, 23.1141, 23.1143, 23.1145, 23.1149, 23.1153, 23.1155, 23.1163, 23.1165, 

23.1181, 23.1182, 23.1183, 23.1189, 23.1191, 23.1193, 23.1203; 

20 
8/24/05 AC 23-

24T 

(5) Title 14 CFR part 23, subpart F, §§ 23.1301, 23.1303, 23.1305, 23.1307, 23.1309, 

23.1321, 23.1322, 23.1329, 23.1337, 23.1351, 23.1353, 23.1357, 23.1359, 23.1435, 23.1438; 

(6) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1505, 23.1513, 23.1521, 23.1527, 

23.1529, 23.1545, 23.1549, 23.1551, 23.1555, 23.1557, 23.1583, 23.1585, 23.1587; 

(7) Title 14 CFR part 34; and 

(8) Title 14 CFR part 36. 

16. What are the applicable regulations and guidance for the installation of a different 

propeller (simple)? 

a. A simple propeller change consists of replacing an originally certificated propeller with a 

different propeller that has the same diameter and number of blades as the original propeller. 

The regulations listed in section 16.b. apply to single engine tractor configuration (Normal 

Category) airplanes only. The impact on the noise levels should be considered and accounted for 

per Title 14 CFR part 36. AC 20-66A provides additional guidance regarding propeller 

installation.

b. The applicable regulations for the installation of a different propeller (simple) should 

include, but are not limited to, the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.33, 23.53, 23.65, 23.71, 23.75, 23.77, 23.201, 

23.251; 

(2) Title 14 CFR part 23, subpart C, §§ 23.301, 23.303, 23.305, 23.307, 23.361, 23.363, 

23.371, (23.573, 23.574, 23.575 as required or if part of original certification basis); 

(3) Title 14 CFR part 23, subpart E, §§ 23.901, 23.905, 23.907, 23.925, 23.1041, 

23.1043, 23.1045, 23.1047; 

(4) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1521, 23.1529, 23.1541, 23.1549, 

23.1559, 23.1581, 23.1583, 23.1585, 23.1587; and 

(5) Title 14 CFR part 36. 

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AC 23-24T 

8/24/05 

17. What are the applicable regulations and guidance for the installation of a different 

propeller (complex)? 

a. A complex propeller change consists of replacing an originally certificated propeller with 

a different propeller that has a different diameter and/or a different number of blades than the 

original propeller. The regulations listed in section 17.b. apply to single engine (Utility, 

Acrobatic, or Commuter Category) and twin-engine reciprocating and turbine airplanes only. 

The impact on the noise levels should be considered and accounted for per Title 14 CFR part 36. 

AC 20-66A provides additional guidance regarding propeller installation.

b. The applicable regulations for the installation of a different propeller (complex) should 

include, but are not limited to, the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.33, 23.45, 23.49, 23.51, 23.53, 23.55, 23.57, 

23.59, 23.61, 23.63, 23.65, 23.66, 23.67, 23.69, 23.71, 23.73, 23.75, 23.77, 23.141, 23.143, 

23.145, 23.147, 23.149, 23.151, 23.153, 23.155, 23.157, 23.161, 23.171, 23.173, 23.175, 23.177, 

23.181, 23.201, 23.203, 23.207, 23.221 (except agricultural and twin engine airplanes), 23.231, 

23.233, 23.235, 23.237, 23.239, 23.251, 23.253; 

(2) Title 14 CFR part 23, subpart C, §§ 23.301, 23.303, 23.305, 23.307, 23.321, 23.331, 

23.333, 23.335, 23.337, 23.341, 23.347, 23.349, 23.351, 23.361, 23.363, 23.367, 23.371, 23.391, 

23.393, 23.395, 23.397, 23.399, 23.405, 23.407, 23.409, 23.415, 23.421, 23.423, 23.425, 23.427, 

23.441, 23.443, 23.445, 23.455, 23.459, 23.571, (23.573, 23.574, 23.575 as required or if part of 

original certification basis); 

(3) Title 14 CFR part 23, subpart D, §§ 23.629, 23.671, 23.672, 23.673, 23.675, 23.677, 

23.679, 23.681, 23.683, 23.685, 23.687, 23.689, 23.691, 23.693, 23.697, 23.699, 23.701, 23.703, 

23.721, 23.723, 23.725, 23.726, 23.727, 23.729, 23.731, 23.733, 23.735, 23.737, 23.745, 23.751, 

23.753, 23.755, 23.757, 23.771, 23.773, 23.775, 23.777, 23.779, 23.781, 23.783, 23.785, 23.787, 

23.791, 23.803, 23.805, 23.807, 23.811, 23.812, 23.813, 23.815, 23.831, 23.841, 23.843, 23.851, 

23.853, 23.855, 23.859, 23.863, 23.865, 23.867, 23.871; 

(4) Title 14 CFR part 23, subpart E, §§ 23.901, 23.905, 23.907, 23.925, 23.929, 23.933, 

23.934, 23.937, 23.939, 23.943, 23.1027, 23.1041, 23.1043, 23.1045, 23.1047, 23.1091, 23.1093, 

23.1121, 23.1149, 23.1153, 23.1155; 

(5) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1505, 23.1507, 23.1511, 23.1513, 

23.1519, 23.1521, 23.1529, 23.1541, 23.1543, 23.1545, 23.1549, 23.1555, 23.1559, 23.1583, 

23.1585, 23.1587; and 

(6) Title 14 CFR part 36. 

22 
8/24/05 AC 23-

24T 

18. What are the applicable regulations and guidance for the installation of auxiliary fuel 

tanks? 

a. AC 23-10 provides additional guidance and criteria for the installation of auxiliary fuel 

tanks. These installations may increase the gross weight of the airplane in which case the 

applicant should refer to the gross weight increase compliance checklist for additional 

requirements. 

b. Performing spin recovery tests with a limited spin matrix should be considered if the 

change to the airplane causes a weight and/or a rotational inertia increase of greater than 10%. 

c. The applicable regulations for the installation of auxiliary fuel tanks should include, but 

are not limited to, the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.23, 23.25, 23.29, 23.147, 23.251, 23.157, 

23.177, 23.181, 23.201, 23.203, 23.221 (except agricultural and twin engine airplanes); 

(2) Title 14 CFR part 23, subpart C, §§ 23.301, 23.303, 23.305, 23.307, 23.321, 23.331, 

23.333, 23.335, 23.337, 23.341, 23.343, 23.471, 23.473, 23.479, 23.485, 23.561, 23.571, 23.572, 

(23.573, 23.574, 23.575 as required or if part of original certification basis); 

(3) Title 14 CFR part 23, subpart D, §§ 23.601, 23.603, 23.605, 23.607, 23.609, 23.611, 

23.613, 23.619, 23.623, 23.625, 23.627, 23.629, 23.777, 23.787, 23.843, 23.853, 23.863, 23.867; 

(4) Title 14 CFR part 23, subpart E, §§ 23.901, 23.903, 23.951, 23.953, 23.954, 23.955, 

23.957, 23.959, 23.961, 23.963, 23.965, 23.967, 23.969, 23.971, 23.973, 23.975, 23.977, 23.991, 

23.993, 23.994, 23.995, 23.997, 23.999, 23.1001, 23.1011, 23.1183, 23.1189; 

(5) Title 14 CFR part 23, subpart F, §§ 23.1301, 23.1305, 23.1309, 23.1337, 23.1351, 

23.1357; 

(6) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1505, 23.1507, 23.1511, 23.1513, 

23.1519, 23.1521, 23.1522, 23.1523, 23.1524, 23.1525, 23.1527, 23.1529, 23.1541, 23.1543, 

23.1549, 23.1553, 23.1555, 23.1557, 23.1581, 23.1583, 23.1585, 23.1589; and 

(7) Title 14 CFR part 36 if the auxiliary tanks are externally mounted or there is a change

to the airplane performance. 

19. What are the applicable regulations and guidance to increase the airplane gross weight? 

a. Many changes may cause an increase in the airplane gross weight. In many cases, due to 

changes in the operational requirements of an owner/operator, the need arises to modify and 

23 
AC 23-24T 

8/24/05 

substantiate the structure for an increase in maximum takeoff weight, in maximum landing 

weight, or in maximum zero fuel weight. 

b. An increase in maximum gross weight is in general a large effort, as it requires a 

complete review of all aspects of the aircraft design. When an airplane is initially designed, the 

manufacturer determines the gross weight through a process of compromise with the desired 

performance features. Once the gross weight is fixed, the details of the aircraft are designed 

around that weight. This means that the basic loads for the aircraft are determined using that 

weight, then the control surfaces and wing area are sized for those loads, and the size of the 

primary structure is determined using the same loads. Most manufacturers over estimate the 

weight by a small percentage to allow for future growth and unforeseen weight increases. This 

margin may be used in some cases to allow a small gross weight increase without changing the 

primary structure, but the applicant must be familiar with all the analysis to determine how much 

margin exists in the design. It must be kept in mind that this margin may exist to mitigate fatigue

and airframe longevity. Gross weight changes that do not involve using this margin in the 

airframe will require a complete re-analysis of the airplane to determine the effect on basic loads, 

performance, and primary structural strength. 

c. A common misconception is that since an airplane has operated over gross weight and 

seems to fly fine, the airplane is good for that weight, and should be granted an approval for 

increased gross weight. The nature of aircraft design is that many airplanes have the capability 

to takeoff and fly well in excess of their allowable gross weight under the right conditions. 

However, the airplane will no longer be able to perform in its entire certificated performance 

envelope. This results in a lower service ceiling, decreased takeoff and climb performance, 

increased landing distance, a decreased ability to withstand the design g-loads without 

deformation, and a decrease in fatigue life of the airframe that could result in early structural 

cracking and possible failure. In the end, this airplane no longer meets the requirements of 14 

CFR part 23, and is less safe than the original design even though it seems to fly fine. 

d. The need for a limited spin matrix on an STC program is a subjective decision based on 

the service history of the specific airplane being modified. It is not possible to offer a 

comprehensive list of when to re-test the spin matrix because of the number of variables to 

consider. There are instances of airplanes with significant modifications that had little effect on 

spin recovery, and airplanes with subtle modifications that changed the spin recovery 

dramatically. If it is determined that the airplane does need to be re-evaluated for spin recovery, 

then a limited matrix using the middle and edges of the envelope is normally all that is needed to 

verify the airplane recovers. Using a limited spin matrix should be considered if the change to 

the airplane causes a weight and/or a rotational inertia increase of greater than 10%. 

e. The applicable regulations to increase the airplane gross weight should include, but are 

not limited to, the following: 

(1) Title 14 CFR part 23, subpart B, §§ 23.21, 23.23, 23.25, 23.29, 23.45, 23.49, 23.51, 

23.53, 23.55, 23.59, 23.63, 23.65, 23.66, 23.67, 23.69, 23.71, 23.73, 23.75, 23.77, 23.141, 

23.143, 23.145, 23.147, 23.149, 23.151, 23.153, 23.155, 23.157, 23.161, 23.171, 23.173, 23.175, 

24 
8/24/05 AC 23-

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(2) 23.177, 23.181, 23.201, 23.203, 23.207, 23.221 (except agricultural and twin engine 

airplanes), 23.231, 23.233, 23.235, 23.237, 23.239, 23.251, 23.253; 

(3) Title 14 CFR part 23, subpart C, §§ 23.301, 23.302, 23.303, 23.305, 23.307, 23.321, 

23.331, 23.333, 23.335, 23.337, 23.341, 23.343, 23.345, 23.347, 23.349, 23.351, 23.369, 23.373, 

23.391, 23.395, 23.397, 23.399, 23.405, 23.407, 23.409, 23.415, 23.421, 23.423, 23.425, 23.427, 

23.441, 23.443, 23.445, 23.455, 23.459, 23.471, 23.473, 23.479, 23.481, 23.483, 23.485, 23.493, 

23.497, 23.499, 23.505, 23.507, 23.509, 23.511, 23.521, 23.523, 23.525, 23.527, 23.529, 23.531, 

23.533, 23.535, 23.537, 23.561, 23.562, 23.571, 23.572, 23.573, 23.574, 23.575; 

(4) Title 14 CFR part 23, subpart D, §§ 23.601, 23.603, 23.605, 23.607, 23.609, 23.611, 

23.613, 23.619, 23.621, 23.623, 23.625, 23.627, 23.629, 23.641, 23.651, 23.657, 23.671, 23.672, 

23.673, 23.677, 23.681, 23.683, 23.687, 23.689, 23.691, 23.693, 23.721, 23.723, 23.725, 23.726, 

23.727, 23.731, 23.733, 23.735, (23.737 if part of type design), 23.751, 23.753, 23.755, 23.757; 

(5) Title 14 CFR part 23, subpart G, §§ 23.1501, 23.1505, 23.1507, 23.1511, 23.1513, 

23.1519, 23.1521, 23.1527, 23.1529, 23.1541, 23.1557, 23.1563, 23.1567, 23.1581, 23.1583, 

23.1585, 23.1587, 23.1589; and 

(6) Title 14 CFR part 36. 

25 (and 26) 

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Appendix 1T 

 APPENDIX 1 – STANDARD COMPLIANCE CHECKLIST 

A1T-1 (and A1-2)