Subject: TYPE CERTIFICATION BASIS Date: 9/30/93 AC No: 23-14 FOR CONVERSION FROM Initiated By: ACE-100 Change:
RECIPROCATING ENGINE TO
TURBINE ENGINE-POWERED PART 23 AIRPLANES
1. PURPOSE. This advisory circular (AC) provides information and guidance concerning an acceptable means, but not the only means of showing compliance with part 23 through amendment 23-45 of the Federal Aviation Regulations (FAR) applicable to replacing reciprocating engines with gas turbine engines (turbopropeller, turbojet, or turbofan). Accordingly, this material is neither mandatory nor regulatory in nature and does not constitute a regulation.
2. RELATED REGULATIONS AND DOCUMENTS.
a. Sections 21.17, 21.19, 21.101(b), 21.113, and 21.115 of part 21 of the FAR; parts 34 and 36 of the FAR.
b. Refer to appendix 1 for a list of related AC's.
3. SCOPE. This AC provides guidance and criteria for establishing the certification basis for installation of gas turbine engines in place of reciprocating engines in general aviation type airplanes certificated to part 23 of the FAR, part 3 of the Civil Air Regulations (CAR), or earlier regulation. It is intended to be used to determine that the engine installation has an acceptable minimum level of safety. Installations that involve changes to primary structure, aerodynamics, airspeed, mass distribution (may induce whirl mode, flutter, and fatigue life changes), maximum weight, system changes, changes in center of gravity (c.g.) limits or power increases which affect high speed characteristics or airplane handling qualities may require additional substantiation and/or additional certification basis requirements that could exceed the scope of this AC. Also, projects such as commuter category or restricted category airplanes will require a more detailed analysis to establish the appropriate certification basis.
4. BACKGROUND. Applications for supplemental type certificates (STC's) and amended type certificates (TC's) for incorporation of gas turbine engines in certificated reciprocating engine airplanes are received by the Federal Aviation Administration (FAA). This guidance is issued because the certification requirements for gas turbine engine installation are substantially different from those for reciprocating engine installation.
5. DESIGNATION OF APPLICABLE REGULATIONS.
a. Type Certificates. In accordance with § 21.19(b)(2), a change from reciprocating engine propeller driven airplanes to turbojet or turbofan engine powered airplanes (not propeller driven), will require a new application for a type certificate. The certification basis will be established in accordance with the type certification procedures in Part 21 of the FAR. For the issuance of a type certificate, an airplane must be shown to comply with the certification basis established in accordance with § 21.17 of the FAR. If the regulations do not provide adequate or appropriate standards because of a novel or unusual design feature, special conditions may be prescribed in accordance with § 21.16.
b. Other Design Changes. For conversion to a turbopropeller driven airplane by the addition of a model to an existing type certificate (amended TC) or modification of an existing model (STC), the airplane must be shown to comply with the certification basis established in accordance with §§ 21.101(b) or 21.115. The engine conversion is a substantially complete redesign of the powerplant installation and compliance with current rules are prescribed in accordance with § 21.101(b). Special conditions may be prescribed in accordance with § 21.16.
c. Commuter Category. For commuter category airplanes, those sections pertaining to commuter category should be included in the certification basis.
d. Restricted Category. A separate AC (AC 21.25-X) for restricted category airplanes will be issued.
e. Environmental Considerations. Parts 34 and 36 of the FAR must be addressed.
6. MODIFICATION CONSIDERATIONS.
a. Before modifying the airplane, the applicant should become familiar with the existing airplane structural and systems characteristics and functions, and with the applicable certification requirements. To avoid structural and systems compatibility problems, an intimate knowledge of the airplane is essential. In particular, the applicant should determine the effects of the turbine engine(s) on payload, c.g., mass distribution induced flutter changes, system changes, airplane operations, and structural margins. An automatic pilot system, if installed should be compatible with the airplane/turbine engine installation and flight test will be required.
b. The applicant should be particularly aware that in the absence of structural substantiation, § 23.1505(c) requires the airspeed indicator red line (VMO/MMO) not exceed Vc (usually top of the old green arc). This may limit operational usefulness of the airplane.
c. Turbine engine conversions typically require a certification flight test program. This may include handling qualities, performance, flutter (not part of FAA flight test), spins, hot fuel climb, engine cooling, engine operating characteristics, autopilot, etc.
d. The list of sections in paragraph 8, Certification Basis, is based on no power increase and no approval for flight in known icing conditions. However, the powerplant installation icing protection requirements are applicable (§ 23.1093).
e. If approval for flight in known icing conditions is requested, flight in icing conditions may have to be demonstrated (§ 23.1419).
f. The applicant should consult with the responsible FAA Aircraft Certification Office (ACO) early in the design program to avoid later changes.
g. Special conditions may be required for engines with electronic engine controls.
7. PROCEDURES. To avoid possible delays and redesign, it is recommended that the applicant follow these procedures after application for approval of the installation.
a. Submit a proposed overall certification plan that identifies the essential steps or actions and the sequence anticipated for submitting drawings, process specifications, reports, analyses, 3
tests, and other documentation to complete the installation approval. This program should include the proposed or target schedule for the required FAA approval tests and inspections.
b. Generate a certification test plan for each required test which describes the analytical procedures and/or certification testing to be used to demonstrate the airplane design. Each plan should list the applicable FAR and describe how each requirement will be met. In addition, the plan should include a description of the airplane or test articles to be used, drawings, method of production (if applicable), and the target date for installation and test. The certification test plan should be submitted for review and approval by the appropriate FAA Aircraft Certification Office (ACO) prior to initiation of tests, to prevent certification delays.
c. Obtain FAA approval of each certification test plan.
d. After the FAA has received the results of the applicants testing per the FAA approved test plans, a Type Inspection Authorization (TIA) will be issued to specify the required installation conformity inspection and official ground and flight tests.
e. Schedule FAA conformity inspection of the test article(s) and installation.
f. Schedule and conduct the ground and flight test(s) with FAA witnessing.
g. Submit final test reports describing all test results and obtain FAA approval.
h. It is recommended that a certification compliance checklist be utilized.
i. It is recommended that the AC index be examined at the time certification projects are initiated to check the available methods of determining compliance with individual regulation sections.
8. CERTIFICATION BASIS. For proper implementation of § 21.101(b) to an STC or amended TC application for turbopropeller engine installation, the type certification basis should include the applicable prior certification basis regulations of the airplane being modified plus at least the latest amendment (through amendment 23-45) of the following sections of part 23 as they apply to the airplane modifications:
9/30/93
23.25
23.33
23.45
23.49
23.65
23.67
23.77
23.145(c)
23.149
23.155
23.161
23.175
23.177
23.201
23.203
23.205
23.221
23.231
23.233
23.239
23.251
23.253
23.301
23.305
23.307
23.335
23.361
23.363
23.367
23.371
23.457(b)
23.479(d)
23.572(b)(3)
23.603
23.627
23.629(e)
23.735(b)
23.777(d)
23.781(b)
23.831
23.863
23.865
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(b)
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 AC 23-14
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
23.1301
23.1303
23.1305
23.1309
23.1321(a), (b), and (c)
23.1322
23.1329
23.1337
23.1351
23.1353(f) and (g)
23.1357(b)
23.1435
23.1438
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 5
If engine power, airspeed limits, propeller rotational speed (revolutions per minute), or number of propeller blades are changed, the applicant should provide substantiating data showing that the vibratory response of the horizontal tail assembly to the propeller slipstream environment will not result in fatigue failures [§§ 23.251, 23.572(a)(1), and 23.572(b)(3)].
BARRY D. CLEMENTS Manager, Small Airplane Directorate Aircraft Certification Service 6
Appendix 1 APPENDIX 1. RELATED ADVISORY CIRCULARS
The advisory circulars (AC's) listed below may be obtained from the U.S. Department of Transportation, General Services Section, M-443.2, Washington, DC 20590:
AC 20-36R Index of Articles (Materials, Parts, Processes and Appliances) Certified Under the Technical Standard Order System AC 20-66 Vibration Evaluation of Aircraft Propellers AC 20-73 Aircraft Ice Protection AC 20-88A Guidelines on the Marking of Aircraft Powerplant Instruments AC 20-110G Index of Aviation Technical Standard Orders AC 20-116 Marking Aircraft Fuel Filler Openings with Color Coded Decals AC 20-119 Fuel Drain Valves AC 20-122A Anti-misfueling Devices:
Use Their Availability and AC 20-124 Water Ingestion Testing for Turbine Powered Airplanes AC 20-128 Design Considerations for Minimizing Hazards Caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor and Fan Blade Failures AC 20-135 Powerplant Installation and Propulsion System Component Fire Protection Test Methods Standards and Criteria AC 23-2 Flammability Tests AC 23-7 Substantiation for an Increase in Maximum Weight, Maximum Landing Weight, or Maximum Zero Fuel Weight AC 23-8A Flight Test Guide for Certification of Part 23 Airplanes 1
Appendix 1 AC 23-10 Auxiliary Fuel Systems for Reciprocating and Turbine Powered Part 23 Airplanes AC 23-12 Structural Substantiation of Part 23 Airplane Modifications Involving Increased Engine Power AC 23.629-1A Means of Compliance with Section 23.629, "Flutter" AC 23.955-1 Substantiating Flow Rates and Pressures in Fuel Systems of Small Airplanes AC 23.959-1 Unusable Fuel Test Procedures for Small Airplanes AC 23.961-1 Procedures for Conducting Fuel System Hot Weather Operation Tests AC 23.1011-1 Procedures for Determining Acceptable Fuel/Oil Ratio as Required by FAR 23.1011(b) AC 23.1309-1A Equipment, Systems, and Installations in Part 23 Airplanes AC 23.1329-2 Automatic Pilot Systems Installation in Part 23 Airplanes AC 23.1419-2 Certification of Part 23 Airplanes for Flight in Icing Conditions AC 36-4B Noise Certification Handbook 2