AC 23-15 Small Airplane Certification Compliance Program, provides historically acceptable means of compliance to selected 14 CFR part 23 rules. STEP 4 provides additional information on this subject.
STEP 3 Part 23 Regulations Not Provided in JAR-VLA
This step covers the instance when no JAR-VLA rule comparable to a part 23 section exists. There are numerous rules in part 23 that were not included in JAR-VLA because it was obvious the rules were not applicable. For example, any rules governing twin engine operations or performance, or turbine engine requirements, are clearly not applicable.
Those rules are not the topic of this section.
Rules addressed by part 23 and not listed in JAR-VLA, but deemed as necessary for part 23 type certification, must be identified in an Issue Paper. The methods of compliance to these specific rules will be documented in the Issue Paper.
STEP 4 Rules Specific to Nighttime or Instrument Operations
The 14 CFR part 23 regulations specific for the desired Night VFR and/or IFR operations must be addressed. The applicant will be required to show compliance to these regulations. You may find a listing of those rules specific to Night-VFR operations, applicable at Amendment level 23-46, in Table 3 of Appendix 1.
4-2. I am an Aircraft Certification Office (ACO) Program Manager. Does an Issue Paper template exist that can be used for each JAR-VLA airplane that seeks part 23 type certification?
Yes, Appendix 1 of this AC contains a sample Issue Paper. This Issue Paper was generated during a recent JAR-VLA/part 23 certification program. It should serve as an excellent starting point for the ACO Program Manager, and improve coordination between the Applicant, ACO Program Manager, and Directorate Project Officer.
A Word About Compliance and our Understanding of the Simplicity of a JAR-VLA Airplane
If you seek a part 23 TC, you should be prepared to demonstrate literal compliance to each rule. However, we understand the inherent level of safety that is fundamental to this airplane, and we believe that the use of an ELOS (or an exemption) may also show compliance to a rule.
A JAR-VLA airplane is not automatically entitled to either of these two methods of compliance. In the case of an ELOS, you will need to demonstrate a safety equivalence, with the understanding that very prescriptive rules are not well suited for findings of ELOS.
In the case of an exemption, you will likely need to incorporate mitigating factors into the airplane design to ensure safety is not adversely affected. You will also need to show how an exemption would be in the public’s interest.
In summary, we feel that a simplified method of compliance to certain 14 CFR part 23 rules may be in order (see AC 23-15). However, it is not an option to relax the applicable requirements of 14 CFR part 23. This has been the single largest source of confusion governing the certification of these airplanes.
AC 23-15 provides rationale that supports simplified methods of compliance to part 23 regulations. This AC does not attempt to identify every 14 CFR part 23 rule not covered by JAR-VLA standards. Rather, it provides a rationale that should be considered when evaluating small airplanes (like JAR-VLA airplanes), with a focus on the inherent level of safety expected of these airplanes.
We understand that many certification requirements in 14 CFR part 23 are not necessary for JAR-VLA airplanes. A careful and deliberate attempt to establish a valid certification basis will ensure that rules deemed unnecessary for a light, single-reciprocatingengine/propeller airplane are not included in the certification basis.
4-3. Is there a process that I should follow to receive FAA certification of my product?
You should follow the certification procedures identified in FAA Order 8110.4B.
4-4. Can I apply for a type certificate (TC) in the utility or acrobatic category?
Airplanes that were previously certificated to JAR-VLA regulations, and that are presented for part 23 type certification, are eligible for type certificates in the normal and utility categories. If you apply for a normal category TC only, then your airplane is limited to the normal category maneuvers described in Section 1.3.
If you apply for a utility category TC only, then your airplane must meet the part 23 utility category requirements and be limited to utility category maneuvers. Per 14 CFR § 23.3(b), utility category maneuvers include:
• Maneuvers permitted under the normal category;
• Spins (if approved for the particular type of airplane);
• Lazy eights, chandelles, and steep turns, or a similar maneuver, with bank angles greater than 60 degrees but less than 90 degrees.
You cannot convert a JAR-VLA approval to a part 23 acrobatic category airplane. If your airplane shows full compliance to all part 23 acrobatic category requirements, then your airplane may be eligible for a type certificate in this category. However, this is well 12
beyond the scope of this AC. We are not aware of any airplane that earned a JAR-VLA approval and then sought a part 23 acrobatic category type certificate.
CHAPTER 5 – RULES OF INTEREST
5-1. Is there any additional information you can provide for 14 CFR, § 23.562, Emergency Landing Dynamic Conditions?
Yes. This rule has garnered the interest of applicants with JAR-VLA airplanes seeking part 23 certification. Previous guidance on this subject has been misinterpreted, leaving applicants to believe that the physical characteristics of the airframe will provide ELOS to this particular rule. This is not true.
For a very prescriptive rule like § 23.562, you should either demonstrate literal compliance to the rule or pursue an exemption. An exemption to § 23.562 is possible provided:
• You can show it is in the public’s interest, and
• You can show safety is not adversely affected.
To show that safety is not adversely affected, you must provide the following mitigating factors in the airframe:
SEAT/RESTRAINT DESIGN
• Each seat is to be equipped with a 4-point harness (a 5-point harness is also acceptable).
• Each seat/harness system must be statically tested to an ultimate load of 3,060 pounds (Note that 18G multiplied by 170 pounds = 3,060 pounds). The lapbelt should react 60 percent of this load, and the upper torso restraint should react 40 percent of this load. You may reference the Society of Automotive Engineers Aerospace Standard AS8049A, pages 16 through 19, for additional information.
HEAD STRIKE (INSTALLATION CONSIDERATIONS)
• The head strike path will be conservatively determined from actual test data, specifically, “Airplane Crash Survival Design Guide, Volume 1 – Design Criteria and Checklists,” report number USAAVSCOM TR 89-D-22A. This report is available, for a fee, from the National Technical Information Service.
You may reach them at 1-888-584-8322 or (703)-605-6050.
• The applicant should overlay the flail envelope from Figure 43 of this document with the cockpit of the airplane.
• The overlay of the head strike path with the cockpit must show that a head strike will not occur.
A request for exemption is a public process, and the public may comment on the exemption request. While we intend to issue an exemption if you satisfy the criteria in this Section, we must either be able to resolve the comments in a successful manner or deny the grant of exemption. You should refer to § 11.81 for further details on the exemption process.
5-2. Is there any additional information you can provide for 14 CFR, § 23.572, Metallic Wing, Empennage, and Associated Structure?
Yes. For part 23 certification, you must show compliance to 14 CFR § 23.572 for metallic wing, empennage, and associated structures.
One acceptable method of compliance to § 23.572 is to establish a fatigue safe-life. For wing structure, we advise establishing a safe-life using the methods contained in FAA report AFS-120-73-2, Fatigue Evaluation of Wing and Associated Structure on Small Airplanes. For empennage structure, we advise using FAA report ACE-100-1, Fatigue Evaluation of Empennage, Forward Wing, and Winglets/Tip Fins on Part 23 Airplanes.
Other acceptable methods of showing compliance to § 23.572 include demonstrating that a structural element will have an “infinite” fatigue life. You can do this by showing that the stresses produced by an appropriate usage loading spectra will not cause fatigue damage to accumulate. You could use a graphical representation of appropriate material S-N data to demonstrate that fatigue damage will not accumulate.
The S-N data you use in this analysis should provide the same probability of a fatigue crack-free life as provided by the AFS-120 report, 99.98 percent probability (equivalent to a 99.82 percent probability with 95 percent confidence). You may need to adjust your S-N data to achieve the AFS-120 probability level using your S-N curve’s statistical properties. Your S-N data should also accurately reflect the stress concentrations, Kt’s, found in your structure.
You should base an appropriate usage spectra on the anticipated usage and an adequate database that defines the loadings expected for that usage. Published sources, including FAA publications, are acceptable databases. Flight test data may be acceptable if statistically significant data is available. However, in some instances, such as water loads on an amphibian airplane, flight data may be necessary to define the usage spectrum.
For aluminum structures, you may use the S-N curve from the AFS-120-73-2 report. At your discretion, a different S-N curve may be used if the S-N curve is for the same material and for the same stress concentration factor, Kt, found in the structure.
5-3. Is there any additional information you can provide for 14 CFR, § 23.573, Damage Tolerance and Fatigue Evaluation of Structure?
14 CFR part 23, § 23.573, addresses both the Damage Tolerance/Fatigue evaluation of the composite airframe structure and the development of the maintenance program for part 23 aircraft.
You will need to use static and fatigue tests to substantiate repairs. You will need to perform these tests on coupons, subcomponents, and full-scale articles. The following is a synopsis of how 14 CFR part 23 addresses repairs for composite aircraft.
14 CFR part 23, § 23.573 requires composite structures and bonded joints to be damage tolerant. The basic building block for damage tolerant design is selecting the largest defect and unrepaired damage allowed in components and assemblies during manufacturing and service. You must be able to inspect for these damage levels. You must also include this damage in the static strength and damage tolerant test articles.
You may use an impact survey to select the appropriate damage criteria to determine the “Threshold of detectability." The testing accomplished will help develop criteria for imparting and inspecting impact damage.
Test specimens from the impact survey form the basis for development of inspection criteria for the quality assurance program. Typical repairs for the damaged specimens are developed and substantiated in the damage tolerant test articles.
Per 14 CFR, part 23, § 23.573 (a)(1): The damaged test article is statically tested up to ultimate load to show sufficient capability with impact damage up to the threshold of detectability.
Per 14 CFR, part 23, § 23.573(a)(2): The test article has damage and is tested under repeated loading to establish the growth rate or no-growth rate of damage that may occur from fatigue, manufacturing flaws or impact damage. You may establish the criteria for "no growth" by visual and ultrasonic inspection. No change in the structural stiffness or strain response may also indicate "no growth." During this part of the test, you may repair some of the defects in order to validate repairs that will become part of the OEM Structural Repair Manual (SRM).
Per 14 CFR, part 23, § 23.573 (a)(3): You will conduct limit load testing at the conclusion of the repeated loading. This will substantiate the residual strength of the aircraft. You must also address loads such as the critical limit flight loads with the combined effects of normal operating pressure and the expected external aerodynamic pressures that the structure must sustain when the airplane is pressurized.
Per 14 CFR, part 23, § 23.573 (a)(4): Based on the data collected during cycle testing, you must establish a rational probability based inspection interval. This interval is 16
specified in the aircraft's Continued Airworthiness Instructions contained in the FAA approved sections of the Aircraft Maintenance Manual.
Per 14 CFR, part 23, § 23.573 (a)(5): You must substantiate the maximum disbonds of each bonded joint for limit load residual strength as indicated by § 23.573 (a)(3). You may determine this by test, analysis or both. A maximum disbond means an entire bondline is missing between any two primary structural components such as the spar/skin, skin/skin, rib/skin or rib/spar.
Per 14 CFR, part 23, § 23.573 (a)(6): Damage tolerant criteria may be impractical for a particular structural component. If so, you must perform a sufficient number of component, subcomponent, element, or coupon tests to establish the fatigue scatter factor and the environmental effects for this component. You must show by tests, or analysis supported by tests, that the component will withstand the repeated loads of variable magnitude expected in service.
In addition, you must perform component, subcomponent, element or coupon tests to establish the fatigue scatter factor and the environmental effects for these structural components.
You may consult AC 20-170A for additional information.
5-4. Do I need to perform a flight flutter test?
Yes. A flight flutter test is required for all part 23 airplane categories. JAR-VLA airplanes that seek part 23 certification will not be exempt from this requirement.
Reference 14 CFR § 23.629 for additional information and requirements.
5-5. Is there any information you can provide for 14 CFR, § 23.1309, Equipment, Systems, and Installation?
Yes. System reliability may be a significant issue when expanding a Day VFR airplane to a Night VFR airplane. The applicant will need to show compliance to § 23.1309 for some of these systems. A thorough discussion on this topic is available in AC 23.1309-1C. We encourage you to review this document, focusing on those areas that discuss Class I applications.
CHAPTER 6 - BACKGROUND OF 14 CFR PART 23 AND JOINT AVIATION REQUIREMENTS – VERY LIGHT AIRPLANES
In the early 1990’s, we attempted to address the burden that the general aviation industry felt was being placed on very light single engine airplanes with low stall speeds. Their concern was that the certification requirements of 14 CFR part 23 were unnecessarily burdensome to these simple, low speed airplanes.
Our action followed a rule making activity undertaken by the JAA, known as “Joint Aviation Requirements for Very Light Aeroplanes,” or JAR-VLA, dated April 26, 1990.
In developing the JAR-VLA standards, the JAA used 14 CFR part 23 to form the basis of the regulation. In an attempt to address the design features of these airplanes, changes and deletions were made to those requirements deemed as either impractical or unnecessary.
Subsequently, we, in conjunction with industry, developed a simplified method to certificate very light airplanes. These airplanes would be treated as a “special class” of airplane under 14 CFR § 21.17(b). The requirements of JAR-VLA would stand as suitable airworthiness criteria for certification of these airplanes, with the following restrictions:
• The airplanes are limited to normal category maneuvers, and
• The airplanes are limited to Day-VFR operations only under 14 CFR part 91.
In addition, JAR-VLA permits the use of engines and propellers certificated to JAR-22, Powered Sailplanes, Subparts H and J. The FAA agrees that these engine and propeller requirements are suitable for JAR-VLA airplanes operating under Day-VFR conditions.
Therefore, a JAR-VLA airplane, equipped with an engine and propeller certificated to JAR-22, Subparts H and J, may earn FAA certification as a special class of airplane under 14 CFR § 21.17(b).
14 CFR part 23 type certification, required for Night-VFR or IFR operations, is a more robust process. The material provided in previous sections of this AC provides guidance to applicants who seek this level of certification.
Appendix 1
ISSUE PAPER
PROJECT: Acme Aircraft Company – Model 123 Night VFR Approval ITEM: G-1 Project No. BR-AWN22 STAGE: 2
REG.REF.: 14 CFR parts 21 & 23 DATE: May 23, 2001 (14 CFR part 21, § 21.17(b), JAR-VLA, VLA-Special Class Category, & 14 CFR part 23)
NATIONAL POLICY REF.: Order 8110.4A, Advisory Circulars
21.17-3 and 23.11-2 ISSUE STATUS: Open SUBJECT: Night-VFR Certification Basis BRANCH ACTION: As required
COMPLIANCE TARGET: Pre-ATC
Night-VFR Certification Basis
STATEMENT OF ISSUE:
Acme Aircraft Company (AAC) has applied for Night-VFR certification for the Model 123 airplane. The country of origin has certificated the Model 123 airplane to the JAR- VLA regulations. The applicable airworthiness regulations, including special conditions as necessary (i.e., the type certification basis), must be designated in accordance with 14 Code of Federal Regulations (CFR) part 21, § 21.101.
BACKGROUND:
The Model 123 is designed and manufactured by AAC. It is a fixed gear, two seat, sideby-side composite aircraft. A conventional elevator on the horizontal stabilizer provides pitch control. It uses a conventional yoke. The propulsion system consists of a TCM IO- 240-B engine and a McCauley fixed pitch propeller - both FAA certified. Its maximum weight is 1,500 pounds (680 kg).
If AAC requested Day-VFR operations only, the aircraft could be certificated as a § 21.17(b) aircraft in the VLA-Special Class category. This method of certification is described in Advisory Circular (AC) 21.17-3, Type Certification of Very Light Airplanes Under Federal Aviation Regulations § 21.17(b), which are eligible for Day-VFR operation only.
A1 However, AAC has made application to include Night-VFR certification in the U.S. type certificate of the Model 123 aircraft.
Appendix 1 FAA POSITION:
The applicable airworthiness regulations must be designated in accordance with § 21.101 of the Federal Aviation Regulations.
The four (4) FAA steps for updating the § 21.17(b) VLA-Special Class airplane to include night certification, as described in AC 23-11-A, are:
Step 1
Review the original application of the Model 123 to determine what the Federal Aviation Regulations part 23 certification basis would have been – which amendment level. Compare this amendment level with Federal Aviation Regulations part 23 amendment 42 (the amendment level of Federal Aviation Regulations part 23 when the JAR-VLA rules were adopted by the FAA) and review the effect on the basic JAR-VLA rules. Update the basic JAR-VLA rules as necessary to reflect the (application date) Federal Aviation Regulations 23 certification basis amendment level.
The application date was 11/11/94. This would have resulted in a certification basis of Federal Aviation Regulations part 23, amendment 46. There are no changes to the basic JAR-VLA as a result of Federal Aviation Regulations part 23, amendments 23-43 through 46.
Step 2
Where JAR-VLA and Federal Aviation Regulations part 23 contain the same rule number but they are substantively different, demonstrate compliance with the Federal Aviation Regulations part 23 rule, request an Equivalent Level of Safety finding, or an exemption, if applicable. AC 23-15 describes simplified methods of compliance for certain Federal Aviation Regulations part 23 requirements.
Listed in Table 1 below are the Federal Aviation Regulations part 23 rules that must be addressed and that are substantively different from the corresponding JAR-VLA rules.
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Appendix 1 TABLE 1
No. Federal Aviation Regulations part 23, amendment 23-46 1 23.45 Performance 2 23.77 Balked Landing 3 23.145 Longitudinal Control 4 23.561 Emerg. Landing Condition, General 5 23.572 Wing, Empennage, & Associated Structure 6 23.629 Flutter 7 23.677 Trim System 8 23.733 Tires 9 23.783 Doors 10 23.807 Emergency Exits 11 23.965 Fuel Tank Tests 12 23.971 Fuel Tank Sump 13 23.1309 Equipment, Systems, and Installations 14 23.1529 Instructions for Continued Airworthiness
Step 3
The JAR-VLA rules address most of the Federal Aviation Regulations part 23 rules that would be applicable for an airplane of this size. Review and address the differences between the JAR-VLA and Federal Aviation Regulations part 23 requirements (at the appropriate Federal Aviation Regulations part 23 amendment level – see Step 1).
Listed in Table 2 below are the Federal Aviation Regulations part 23, amendment 46 rules that must be addressed but are not contained in the JAR-VLA rules:
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Appendix 1 TABLE 2
No. Federal Aviation Regulations part 23, amendment 23-46 1 23.3 Special Retroactive Requirements 2 23.31 Removable Ballast 3 23.53 Takeoff Speeds 4 23.253 High Speed Characteristics 5 23.302 Canard or Tandem Wing Configurations 6 23.507 Jacking loads 7 23.509 Towing Loads 8 23.511 Ground Load; Unsymmetrical Loads on Multiple-Wheel Units 9 23.562 Emergency Landing Dynamic Conditions 10 23.573 Damage Tolerance and Fatigue Evaluation of Structure 11 23.851 Fire Extinguishers 12 23.867 Lightning Protection of Structure 13 23.954 Fuel System Lightning Protection 14 23.997 Fuel Strainer or Filter 15 23.1043 Cooling Tests 16 23.1107 Induction System Filters 17 23.1157 Carburetor Air Temperature Controls 18 23.1181 Designated Fire Zones; Regions Included 19 23.1311 Electronic Display Instrument Systems 20 23.1329 Automatic Pilot System 21 23.1335 Flight Director System 22 23.1391 Minimum Intensities in the Horizontal Plane of Position Lights 23 23.1393 Minimum Intensities in any Vertical Plane of Position Lights 24 23.1397 Color Specifications 25 23.1413 Safety Belts and Harnesses 26 23.1441 Oxygen Equipment and Supply 27 23.1443 Minimum Mass Flow of Supplemental Oxygen 28 23.1445 Oxygen Distribution System 29 23.1447 Equipment Standards for Oxygen Dispensing Units 30 23.1449 Means for Determining Use of Oxygen 31 23.1523 Minimum Flight Crew 32 23.1524 Maximum Passenger Seating Configuration 33 23.1527 Maximum Operating Altitude 34 23.1553 Fuel Quantity Indicator 35 23.1563 Airspeed Placards 36 23.1567 Flight Maneuver Placard
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