23.865 Fire protection of flight controls, engine mounts, and other flight structure
There is no corresponding rule in CAR 3.
The corresponding airworthiness criteria is section 4.41, Airship Design Criteria, FAA-P-8110-2, Change 2.
Amendment 23-14 and Subsequent
A proposed revision in NPRM 71-13 explains this amendment as follows:
“Experience has indicated the need to ensure that flight controls and flight structure in powerplant fire zones remains operable in the event of a fire. The proposal requires this.”
Amendment 23-45 and Subsequent
A proposed revision in NPRM 90-18 added “engine mounts” to the amendement with the following explanation: “This proposal clarifies existing Section 23.865 by excluding those portions of the engine mount certificated with the engine from this section. Additionally, a clarification is provided to address the allowable damage expected on engine isolators.”
The engine mounts refer to the aircraft structure for mounting the engine and not the mount pads or attachment points, which are integral parts of the engine.
The intent of the regulations on engine mounts is the engine remains in place with a fire heating an engine mount. FAA does not intend to cover the case of a general conflagration where the entire engine compartment is burning. Therefore, an applicant should design enough load paths for the engine to remain in place with a localized fire.
For purposes of this rule, landing gears are not considered to be flight structures, so fireproofing or shielding landing gears are at the option of the manufacturer.
Shielding made from fireproof materials in part 23, § 23.1191(h), may be used without flame testing. While the shielding may be made of fireproof materials that do not require testing, means of installing the shielding such as sealers and adhesives should be shown not to reduce the efficacy of the shielding. Shielding materials subject to corrosion should be appropriately protected. Shielding need not be fireproof if it protects the enclosed structure to an extent equivalent to the enclosed structure being fireproof by itself.
The effectiveness of such shielding or fireproof materials should be determined by subjecting the shielded or fireproof structure, or control, to flammability testing as defined in AC 23-2A, “Flammability Tests.” Before removal of the flame at the end
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162 of the test, loads should be applied to the shielded structure or control to show that it can withstand the loads expected to occur during completion of the flight. These loads can be treated as ultimate loads. Without a more rationale determination of the expected flight loads, a load factor of 70 percent of maneuver load or 40 percent of gust load is superposed with the loads from the engine thrust and torque for maximum continuous power. After five minutes and until the end of 15 minutes the engine may be assumed to be shutdown.
Amendment 23-48 and Subsequent
Policy on compliance of 14 CFR, part 23, § 23.865 at Amendment 23-48 for Structures in Adjacent Areas Subjected to Effects of Fire in Designated Fire Zones
The revision of 14 CFR, part 23, § 23.865 at Amendment 23-48 includes:
1. changing the words “engine compartment” to “designated fire zones” for consistency with §§ 23.1181 and 23.1203; and
2. adding the phrases “adjacent areas that woul d be subjected to the effects of fire in the designated fire zones.”
The intent of this section in the rules is to require the materials and components, in the designated fire zone, that are essential to flight safety: 1) be fabricated either from a material meeting defining fireproof under Title 14, part 1.1, or 2) be shown capable of maintaining their integrity or performing their function under the conditions of fire at least as well as steel. The intent of this section is also to require that materials and components, in adjacent areas to a designated fire zone, that are essential to flight safety, be capable of: 1) maintaining their integrity or 2) performing their function under the conditions of fire in the designated fire zone.
The fire condition characterized by a 2000-degree Fahrenheit (F) flame can be treated as a failure condition that should not prevent continued safe flight and landing for at least 15 minutes. The rule requires the structures (composite and metallic) behind the firewall and subjected to the heat effects of the fire be able to withstand the flight loads expected to occur during completion of the flight. It also requires these flight loads to not be less than the gust loads expected to be encountered during the completion of the flight. These loads can be treated as ultimate loads. Design features, including multiple load path arrangement, can be considered when establishing the remaining structural capacity. Freedom from flutter and whirl mode should also be shown.
Compliance with this requirement must be shown by tests, or by analysis supported by tests. Assessing heat effects needs to include all heat transf er mechanisms that may occur. For composite structure, the long-term environmental effects that may degrade the mechanical properties of the structures also need to be considered. These may include the effects due to moisture and steam pressure.
163 EASA AMC effective February 12, 2009, AMC 23.865 is acceptable for FAA certification.
164 Section 7. Electrical Bonding And Lightning Protection
23.867 Electrical bonding and protection against lightning and static electricity
There is no corresponding rule in CAR 3.
The corresponding airworthiness criteria is section 4.42, Airship Design Criteria, FAA-P-8110-2, Change 2.
Amendment 23-7 and Subsequent
A proposed revision in NPRM 67-14 explains this amendment as follows: “Small airplane operations involving potential exposure to lightning strikes are increasing.
The hazardous effects of lightning on aircraft are well known. Economically practical means of protecting aircraft from such effects have been under study for several years. In order to prevent undue dictation of design, and yet, on the other hand, avoid an unnecessarily vague standard, this proposal summarizes the design objectives derived from the studies and experience obtained in the field of lightning protection of aircraft structures.”
Amendment 23-7 states: “The Final Rule notice proposed to add a new Sec. 23.581 to require lightning protection of the airplane structures. The designation of that amendment has been changed to new Sec. 23.867 since it is a design and construction requirement and should be included in Subpart D of Part 23. One comment objected to the proposal, citing a report regarding a particular airplane which indicated that the recorded lightning strikes on that airplane had not been catastrophic. The report does not, however, cover the numerous other small airplanes and does not establish that lightning strikes would not be catastrophic for small airplanes. Another commentator suggested that the requirement be applied only to all-weather airplanes.
While the term "all-weather" is not defined, service experience has established that lightning strikes occur most frequently along frontal patterns and squall lines in VFR conditions. A third comment stated that the proposal was a satisfactory general statement but that it should be supported by guidance material. General information about lightning and its effect on aircraft is available (Advisory Circular No. AC 20-
53). The FAA believes that the proposal is clear and that no change is warranted.
Except for the change in section number, the amendment is adopted as proposed.”
Lightning protection of Visual Flight Rules (VFR) airplanes was considered because there is a possibility that a lightning strike on a VFR airplane could occur. However, the probability of a lightning strike during VFR operations is low, and consequences of a lightning strike are generally minor if good airplane design practices are followed. Therefore, compliance to this section for VFR-only airplanes may be achieved by following accepted design practices, without specific certification lightning tests or analysis. Accepted design practices may be found in DOT/FAA/CT-89/22, Aircraft Lightning Protection Handbook, September 1989.
165 For VFR-only airplanes, an applicant should submit a certification plan that describes the airplane lightning protection design for structure, controls, and systems.
Compliance may be demonstrated by any of the following: Design review, reference to aircraft lightning protection design handbooks, calculations or analysis, lightning test data, or system lightning qualification.
For any other airplane, an applicant should submit a certification test plan describing the analyses or tests to be used to show lightning protection effectiveness. The lightning compliance should, as a minimum, include the following steps:
a. Define the lightning zones for the entire aircraft, and describe the method for determining the zones, such as lightning strike attachment model tests, similarity to previous airplane designs, or service experience.
b. Evaluate the lightning direct effects protection for all flight critical portions of the airframe, flight controls, and propulsion systems. Define the lightning qualification tests and damage assessment procedures. Fuel system lightning protection compliance should be demonstrated by compliance to 23.954.
c. Evaluate lightning indirect effects protection for the airplane and its electrical and avionics systems. Include both upset and damage assessment for the electrical and avionics systems.
d. Define the test procedures, test parameters, analysis methods simulation techniques, and lightning waveforms and test voltages and currents used to demonstrate the lightning protection compliance.
e. Define the airplane grounding and bonding design features, particularly for composite structures. Demonstrate airplane grounding and bonding tolerance to environments such as vibration, temperature and corrosion.
Define instructions for continued airworthiness of the airplane lightning protection, including maintenance practices and repairs for structure.
The following documents are applicable:
AC 20-155, SAE Documents to Support Aircraft Lightning Protection Certification.
This AC states that SAE ARP5412A, Aircraft Lightning Environment and Related Test Waveforms, and ARP5414A, Aircraft Lightning Zoning, are acceptable for certification.
AC 20-53B, Protection of Aircraft Fuel Systems Against Fuel Vapor Ignition Caused by Lightning. This AC addresses ignition hazards caused by direct effects on main and auxiliary fuel tanks, fuel tank components and plumbing, and the indirect effects (upset or damage) on analog or digital electronic and electrical systems that could
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166 lead to ignition hazards on wires or equipment such as fuel quantity probes located in a fuel tank cavity containing fuel vapor.
AC 20-136A, Protection of Aircraft Electrical / Electronic Systems Against the Indirect Effects of Lightning,” December 21, 2006.
SAE ARP 5412A, “Aircraft Lightning Environment and Related Test Waveforms,” February 21, 2005.
SAE ARP 5414A, “Aircraft Lightning Zoning,” February 16, 2005.
SAE ARP 5415A, “Users Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning,” May 14, 2002.
SAE ARP 5416, “Aircraft Lightning Test Methods, “March 17, 2005.
SAE ARP 5577, "Aircraft Lightning Direct Effects Certification,” September 30, 2002.
Amendment 23-49 and Subsequent
A proposed revision in NPRM 94-21 explains the change in the title of § 23.867 as follows: “This proposed revision would change the heading that precedes the section from "Lightning Evaluation" to "Electrical Bonding and Lightning Protection." It would also revise the section heading form "Lightning protection of structures" to "Electrical bonding and protection against lightning and static electricity." The proposed revisions more accurately clarify the content of the section.”
167 Section 8. Miscellaneous
23.871 Leveling means
The corresponding rule in CAR 3 is CAR 3.401.
The corresponding airworthiness criteria is section 4.50, Airship Design Criteria, FAA-P-8110-2, Change 2.
Amendment 23-7 and Subsequent
The original rule required “reference marks.”
This amendment has the following explanation in NPRM 67-14: “any means, not just reference marks, are acceptable for leveling the airplane on the ground.”
168 Chapter 2 – Subpart F-Equipment
Section 1. General
23.1301 Function and installation
The corresponding rules in CAR 3 are CAR 3.651 and 3.652.
The corresponding airworthiness criteria is section 6.1, Airship Design Criteria, FAA- P-8110-2, Change 2.
Original Issue and Subsequent
Bench level environmental testing is required for Technical Standard Order Authorizations. It is acceptable data for Type Certificate, Amended Type Certificate, Supplemental Type Certificate and Parts Manufacturer Approval. Policy Memorandum “Standardization and Clarification of Application of 14 CFR Part 23, §§ 23.1301 and 23.1309, Regarding Environmental Qualification”; PS-ACE100- 2005-10039, dated February 16, 2006, provides additional guidance.
Standardization and Clarification of Application of 14 CFR Part 23, §§ 23.1301 and
23.1309, Regarding Environmental Qualification
Summary
This guidance applies to FAA’s 14 Code of Federal Regulations (CFR) part 23, §§ 23.1301 and 23.1309, Amendment 23-41 or later for environmental qualification.
The guidance allows the depth of the environmental qualification to be commensurate with the severity of the hazard. It is based on the five failure condition classifications defined in AC 23.1309-1E ranging from no safety effect to catastrophic. This policy should reduce the amount of environmental qualification, especially for equipment that has no safety effect and equipment that has only minor failure conditions.
Background
For part 23 airplanes, most certification of equipment for environmental qualifications was the same for all the equipment regardless of its failure condition.
In the past, applicants and certification authorities interpreted § 23.1301(d), Function properly when installed, from Amendment 23-20, to mean that equipment, even if it was not required or pertinent to safety, should have the same environmental qualification as equipment essential to safe operation. For airplanes with certification basis including § 23.1309, Amendment 23-41 or later, the FAA is clarifying the interpretation of § 23.1301(d) to focus this activity on items either required by the regulations or having an effect on safety. This interpretation is based on the notice for Amendment 23-20 stating that the main purpose of the amendment is to prevent hazards.
The environmental qualifications will be determined by the failure conditions of the equipment, as defined in AC 23.1309-1E. Currently, software and hardware developmental assurance levels, probability of failures, and lightning and High Intensity Radiated Fields (HIRF) protection levels are determined by the failure condition classification.
Definitions
Equipment Essential to Safe Operation: Equipment installed in order to comply with the applicable certification requirements of part 23 or operational requirements of parts 91 and 135. Also, for environmental qualifications, equipment or a system that has a failure or malfunction that results in anything from minor, to major, to hazardous, to catastrophic failure conditions as defined in AC 23.1309-1E.
Hazard: Any condition that compromises the overall safety of the airplane or that significantly reduces the ability of the flight crew to cope with adverse operating conditions.
Current Airworthiness Regulations, Advisory Material of 14 CFR Part 23, and RTCA Documents or the latest version.
§ 23.1301, Function and installation
§ 23.1309, Equipment, systems, and installations
AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes
RTCA/DO-160F, Environmental Test Conditi ons and Test Procedures for Airborne Equipment or equivalent
14 CFR part 23, §§ 23.1301 and 23.1309: These sections contain the general regulatory requirements for the environmental qualifications of installed equipment.
The level of qualification depends on the five failure condition classifications, as defined in AC 23.1309-1E. These classifications are no safety effect, minor, major, hazardous, and catastrophic. TSO articles must also meet the requirements of
23.1301 and 23.1309 when installed in Part 23 aircraft.
Section 23.1301 requires that the installed equipment perform its intended function.
Section 23.1309 requires equipment to not adversely affect equipment essential to safe operation of the airplane or affect other equipment without indicating the effects to the pilot. The following paragraphs provide guidance for environmental qualification for each of the failure condition classifications:
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Equipment with major, hazardous, and catastrophic failure conditions:
Applicants should design and install the equipment and systems to perform as intended under the anticipated airplane’s operating and environmental conditions that the equipment will encounter. For environmental qualification when using RTCA/DO-160F as an acceptable method of compliance, the applicant must present the appropriate sections and category levels for the airplane installation and environment to the FAA ACO. Equivalent testing methods, analyses, ground or flight tests, and qualification by similarity are also acceptable.
Following the appropriate levels of RTCA/DO-160F may be the most cost effective means for an applicant to comply, because other means of compliance may require more tests and more difficult testing. Testing for the indirect effects of lightning is also required for all of these failure conditions. For systems that have a catastrophic failure condition, testing for HIRF is required. When the proposed regulation is finalized for HIRF, testing for HIRF will also be required for all these failure conditions. For indirect effects of lightning or HIRF, additional guidance is in AC
23.1309-1E and this AC.
Equipment with minor or no safety effect failure conditions: Applicants should design and install the equipment and systems so they perform as intended under the airplane’s operating and environmental conditions that the equipment will encounter.
The applicant should install the equipment and systems in a way that does not adversely affect equipment essential to safe operation. In some cases, the FAA would only accept a ground or flight installation evaluation, or both. If the applicant is using ground or flight installation evaluation for compliance, instructions for these evaluations should consist of good engineering practices. It should include the appropriate operations modes and phases of flight. Although, the FAA would still accept qualitative evaluations for the specific airplane, it may be more efficient to address the environmental requirements by complying with the appropriate sections and levels of RTCA/DO-160. Testing for HIRF and the indirect effects of lightning is not required.
Equipment with no safety effect failure conditions: The primary purpose for environmental testing is to determine the performance characteristics of the equipment. The equipment should function when installed as intended by the manufacturer’s instructions; however, the focus should not be on the reliability of its operation for all installation environments.
Ground and flight evaluations for all equipment installations: The equipment and systems should be installed in a way that does not adversely affect equipment essential to safe operation. The evaluations should determine that neither normal operation nor failure of the equipment would pose a hazard.
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171 Similarity: For any failure condition it is acceptable for all equipment to show compliance without the need for additional tests by similarity. Only slight differences may exist between the previously certified system and installation and the new system and installation. To use similarity, there must be adequate service history. If there were any problems reported, there should be an adequate history with the product with the changed design to ensure the problems were resolved. A qualitative demonstration of similarity may be acceptable. The applicant is responsible for showing there are only slight differences between the products. If uncertainty exists about the effects of the differences, either additional tests or analysis, or both, should be conducted as necessary to resolve the open issues. Similarity may not apply for a combination of a new aircraft design and a new system design including approved model list.
Conformity: The product or part must have the appropriate design data, approved procedures, and processes to determine conformity of the product or part.
Conformity should be established for all parts with major, hazardous, and catastrophic failure conditions. For parts with minor or no safety effect failure conditions, conformity is recommended. However, if there is no conformity of the parts, when the part is replaced, the new part should be tested for its performance characteristics.
For additional specific environmental qualification guidance, see AC 23.1309-1E, RTCA DO-160F, and the applicable TSO.
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172 The following table summarizes the environmental qualification process for each failure condition.
Table 1. A Summary for Environmental Qualification as Related to Failure Condition Classifications
Failure Condition Classification Environmental Qualification Catastrophic Must function properly wh en installed. Does not affect other equipment essential to safe operation.
HIRF is required for all equipment.
Testing for indirect effects of lightning is required.
Normally, environmental testing using, RTCA/DO-160, or similarity.
Hazardous Must function properly when installed. Does not affect other equipment essential to safe operation.
Testing for the indirect effects of lightning is required.
Normally, environmental testing using RTCA/DO-160, or similarity.
Major Must function properly when installed. Does not affect other equipment essential to safe operation.
Testing for the indirect effects of lightning is required.
Normally, environmental testing using RTCA/DO-160, or similarity.
Minor Must function properly when installed. Does not affect other equipment essential to safe operation.
It may comply by ground or flight evaluation, or both, or similarity. If several airplane models are involved, it may be more efficient to use RTCA/DO-160.
No safety effects Must function properly when installed. Does not affect other equipment essential to safe operation.
It may comply by ground or flight evaluation, or both, or similarity. If several airplane models are involved, it may be more efficient to use RTCA/DO-160.