23.863 Flammable fluid fire protection Amendment 23-23 and Subsequent Those areas where ignition sources and flammable fluids are present must be designated as flammable fluid zones, and measures must be taken to minimize the probability of ignition sources and leakage being present. This is followed by a means to minimize the effects once a fire has occurred. This could be accomplished by extinguishing, ventilation, isolation, drainage, etc. The rule does not go so far as to make the entire airplane a “designated fire zone.”
Fire detection and extinguishing is believed to be impractical for many part 23 airplanes.
Where fire detection and extinguishing means might be impractical, the back up provisions could, for example, consist of a means to limit fluid leakage and fireproofing or isolation of critical parts. Therefore, compliance with § 23.863 could be accomplished with a means to limit fluid leakage, minimizing the probability of ignition, fireproofing or isolating critical parts.
Minimization of ignition requires that equipment where a single failure can cause flammable fluid leakage, be tested to the explosion proof standards in RTCA/DO-160.
If a finding is made that flammable fluids or vapors cannot escape into an area containing a potential ignition source or if the fluids are nonflammable, this rule would not apply to that area. Design measures could support the finding such as (1) shrouding (sealing off) of all potential ignition sources; or (2) shrouding or sealing off of all flammable fluid/vapor sources.
In either case, it should be ascertained that the means will continue to serve its function following any single failure of the system or component it is isolating from the area.
23.865 Fire protection of flight controls, engine mounts, and other flight structure Amendment 23-14 and Subsequent 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 regarding engine mounts is that the engine remains in place with a fire heating an engine mount. We do not intend to cover the case of a general conflagration where the entire engine compartment is burning. Therefore, an applicant should design sufficient 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 is 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 don’t require testing, means of installing the shielding such as sealers, adhesives, etc. should be shown to not 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 23-2, Flammability Tests. Before removal of the flame at the end of the test, loads should be applied to the shielded structure or control to demonstrate that it can withstand the loads expected to occur during completion of the flight. These loads can be treated as ultimate loads.
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:
- changing the words “engine compartment” to “designated fire zones” for consistency with §§ 23.1181 and 23.1203; and
- adding the phrases “adjacent areas that would be subjected to the effects of fire in the designated fire zones.”
135 The intent of this section in the rules is to require that the materials and components, in the designated fire zone, that are essential to flight safety be fabricated from a material meeting the definition of fireproof under Title 14 Part 1.1 or be shown to be 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 maintaining their integrity or performing their function under the conditions of fire in the designated fire zone.
The fire condition characterized by a 2000° F flame can be treated as a failure condition that should not prevent continued safe flight and landing for at least fifteen (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 taken into account when establishing the remaining structural capacity. Freedom from flutter and whirlmode should also be demonstrated.
Compliance with the above requirement must be demonstrated by tests, or by analysis supported by tests. The assessment of heat effects needs to include all heat transfer mechanisms that may occur in the area of concern. For composite structure, the longterm 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.
JAA ACJ 23.865 is acceptable for FAA certification.
ELECTRICAL BONDING AND LIGHTNING PROTECTION
23.867 Electrical bonding and protection against lightning and static electricity Amendment 23-7 and Subsequent Lightning protection of VFR airplanes was considered because there is a possibility that a lightning strike on a VFR airplane could occur. However, the probability and consequences of a VFR lightning strike are more pertinent than the possibility. The hundreds of millions of hours of service history on metallic airplanes illustrate neither a probability nor a consequence worthy of requiring the customer’s assets be expended on lightning certification of this class of airplane. Therefore, this section is not applicable to VFR-Only airplanes that have electrical-bonding characteristics commensurate with metallic construction.
Protection of Composite Structure and Installed Equipment from the Direct and Indirect Effects of Lightning Unless VFR-Only, per the preceding paragraph, an applicant should submit a certification test plan describing the analyses/testing to be used to demonstrate lightning protection effectiveness. At a minimum, the test plan should describe the sub-components, components, and systems to be tested and include the following:
a. Zone definition of the entire aircraft (show how this will be accomplished—strike attachment model tests, similar design, etc.).
b. Full scale or other acceptable means of simulated lightning qualification test on all flight critical portions of the airframe, flight controls, fuel, propulsion, electrical and avionics systems, including damage assessment procedures.
c. The indirect effect on the airplane and its systems after a direct lightning strike must also be evaluated. This will include both upset and damage assessment to the electrical and avionics systems.
d. Values for each phase of the protection should be delineated. This includes test procedures, test parameters, methodology and simulation techniques to be used during the validation phase.
e. Grounding and bonding concerns are paramount in any aircraft but are more critical in composite structures. The test plan must address these areas and include life cycle environmental tests.
f. Lightning simulation methods including test voltages and current waveforms must be defined.
g. The test plan should address maintenance practices and repairs to the structure that ensure the continued lightning protection effectiveness.
The following SAE documents are applicable:
SAE ARP 5412, Aircraft Lightning Environment and Related Test Waveforms.
SAE ARP 5413, Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning, (being converted to an AC, AC 20-136A).
SAE ARP 5414, Aircraft Lightning Zoning.
SAE ARP 5415, User’s Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning.
MISCELLANEOUS
23.871 Leveling means No policy available as of June 30, 2001.
139 Subpart F—Equipment
GENERAL
23.1301 Function and installation Original Issue and Subsequent When performing Technical Standard Order (TSO) testing to RTCA/DO-160, Sections 16 and 17, the sentence “After exposure. DETERMINE COMPLIANCE WITH APPLICABLE EQUIPMENT PERFORMANCE STANDARDS” is considered to refer to the appropriate section of the RTCA Minimum Operational Performance Standards (MOPS) that references DO-160.
For a test section of a MOPS that is titled “Normal Operating Conditions,” the applicable equipment standards should be met while the test is being conducted. If the equipment experiences an interruption of operation as a result of the test, then the acceptability of the duration of the interruption will depend on the intended function of the equipment and must be justified.
Manual resets or pilot actions required to restore normal operation following any test must be explicitly permitted by the applicable TSO or MOPS. If the TSO or referenced MOPS does not specifically allow for a reset, then the equipment must continue to operate or resume normal operation without any pilot action.
Instruments and equipment installed to meet the requirements of 14 CFR part 23, § 23.1303 and part 91, § 91.205 should meet the Technical Standard Order requirements that are applicable for that instrument or equipment or equivalent requirements.
Original Issue through Amendment 23-19 A system/equipment that is neither essential for safe operation nor required by airworthiness or operating rules may be approved if it is not a hazard in normal operation or when it malfunctions/fails. It does not have to perform its intended function.
Section 23.1301 requires that instruments be installed in accordance with prescribed limitations. Therefore, if an instrument manufacturer specifies any allowable installation requirements (i.e., panel slope for gyroscopic instruments), the installer should stay within the limitation(s).
Each piece of installed equipment must be labeled as to its identification, function or operating limitations or any combination. This applies to the manufacturer of the equipment
140 not the installer. The installer is required to verify the intended function and make any placards or flight manual limitations per Subpart G that the installed equipment makes necessary.
See AC’s 23-8A, Flight Test Guide for Certification of Part 23 Airplanes; 20-67B, Airborne VHF Communications Equipment Installations; and 20-41A, Substitute Technical Standard Order (TSO) Aircraft Equipment.
Amendment 23-20 and Subsequent All installed systems/equipment should perform their intended functions. For systems/equipment neither essential for safe operation nor required by airworthiness or operating rules, the manufacturer should define the intended functions that the FAA will verify as part of the certification project.
Section 23.1301 requires that instruments be installed in accordance with prescribed limitations. Therefore, if an instrument manufacturer specifies any allowable installation requirements (i.e., panel slope for gyroscopic instruments), the installer should stay within the limitation. We recommend that the slope be no more than 15°. If applicants want a slope greater than 15°, they should show conclusively by tests or analyses that the instrument will function properly when subjected to all expected airplane maneuvers.
Each piece of installed equipment must be labeled as to its identification, function or operating limitations or any combination. This applies to the manufacturer of the equipment not the installer. The installer is required to verify the intended function and make any placards or flight manual limitations per Subpart G that the installed equipment makes necessary.
There has been a trend to install equipment, mainly navigation related such as moving maps, as non-required, “Not approved for primary navigation” or “Situation Awareness Only (SA- Only).” The basis for certification has been to perform its intended function and not present a hazard per this section. Instruments that aid situational awareness should be certified per the requirements in § 23.1309, functional hazard assessment. It is not acceptable to label an instrument as “SA-Only” and assume its failure in normal operation is acceptable. It is also unacceptable to place such an instrument in the primary field of view of the pilot. Based on history where pilots have tended to fly to known failed gyroscopic instruments, they cannot be expected to ignore an instrument in this position. Last, it is not acceptable to install an instrument as non-required and use its outputs as input data to required instruments.
Guidance for Required Instruments The purpose of this guidance is to provide clarification on instrument and equipment requirements that are required by 14 CFR part 91, § 91.205 for part 23 airplanes.
141 Instruments and equipment installed to meet the requirements of § 91.205 should meet the Technical Standard Order (TSO) or equivalent requirements. Technical Standard Order or equivalent requirements are an acceptable means of compliance for the instrument or equipment standards for installation in part 23 airplanes. The pertinent requirements in 14 CFR part 23 for the basis of the above statement are as follows:
(1): Section 23.1301 Function and installation.
Each item of installed equipment must--
(a) Be of a kind and design appropriate to its intended function.
(b) Be labeled as to its identification, function, or operating limitations, or any applicable combination of these factors;
(c) Be installed according to limitations specified for that equipment;
and
(d) Function properly when installed.
And
(2): Section 23.1525 Kinds of operation.
The kinds of operation authorized (e.g., VFR, IFR, day or night) and the meteorological conditions (e.g., icing) to which the operation of the airplane is limited, or from which it is prohibited, must be established appropriate to the installed equipment.
Accuracy of the Magnetic Gyroscopically Stabilized Heading System PURPOSE.
The purpose of this guidance is to provide information on accuracy of the magnetic gyroscopically stabilized heading system that can be displayed on a Horizontal Situation Indicator (HSI) installed in part 23 airplanes.
The operating rules such as 14 CFR part 91 and 14 CFR part 135 specify the minimum required equipment that must be installed based in part 23 airplanes for the type of operation, such as Visual Flight Rules (VFR) or Instrument Flight Rules (IFR). 14 CFR part 91, § 91.205 requires for heading information; under VFR operation, a magnetic non-stabilized direction
142 indicator (i.e. compass) is required and; in addition under IFR operation, a gyroscopically stabilized heading system is required.
The general airworthiness requirements in 14 CFR part 23, § 23.1301 and § 23.1525, determine the flight instrument and equipment accuracy requirements for part 23 airplanes. Part 23 does not prescribe specific accuracy requirements for magnetic gyroscopically stabilized heading systems. Specific accuracy requirements for avionics may be found in Technical Standard Orders and as acceptable means of compliance to § 23.1301 in advisory circulars, notices, or policy statements/letters.
ACCURACY REQUIREMENTS:
Magnetic Non-Stabilized Direction Indicator. A magnetic non-stabilized direction indicator (compass) is required (reference § 23.1327) to have an accuracy of ±10º or have a correction card, placard, or a back-up gyroscopic direction indication provided that indicator has an accuracy better than ±10º. If the sole purpose of the gyroscopic direction indication is for backing up the magnetic non-stabilized direction indicator, then the accuracy of displayed headings can also be to ±10º. However, if a gyroscopic direction indicator is installed to meet the IFR operating rules, then the installation requirements are defined by § 23.1301.
Magnetic Stabilized Gyroscopically Stabilized Direction Indicator. An installed final accuracy for a magnetic stabilized gyroscopically direction indicator of ±4º on the ground or ±6° in normal level flight on any heading would meet the requirements of 14 CFR part 23, § 23.1301. This accuracy applies after compensation and should include cumulative errors in all combinations due to:
• the equipment itself,
• the current flow in any item of electrical equipment and its associated wiring,
• the movement of any component, (e.g. controls or undercarriage), and
• the proximity of any item of equipment containing magnetic material direction indicators
COMPARATOR MONITOR For systems installations that include two magnetic gyroscopically stabilized heading systems and a comparator that monitors the differences between the headings of the two systems, the comparator trip point set as follows would meet the requirements of 14 CFR part 23, § 23.1301:
• 6º in stabilized level flight.
• 6º plus ½ of the bank angle; or
• 12º with a bank angle greater than 6º ;
• The alert function can be disabled at a bank angle greater than 20º.
• An alert is provided if the condition exceeds 60 seconds, but allow two minutes for a turn error as stated in the TSO.
It should be noted that the 6º trip point during level flight actually permits a heading error of as much as 12º. This would be comprised of one system at the 6º in-flight tolerance limit while the other system, presumably with some sort of malfunction, could have an error of 12º in the same direction before the comparator monitor alert is tripped.
BACKGROUND INFORMATION. The following background information is provided for additional information.
EQUIPMENT REQUIREMENTS.
Instruments and equipment installed to meet the requirements of § 91.205 should meet the Technical Standard Order (TSO) or equivalent requirements. Technical Standard Order or equivalent requirements are an acceptable means of compliance for the instrument or equipment standards for installation in small airplanes. The pertinent requirements in 14 CFR part 23 for the basis of the above statement are as follows:
Section 23.1301, Function and installation.
Each item of installed equipment must--
(a) Be of a kind and design appropriate to its intended function.
(b) Be labeled as to its identification, function, or operating limitations, or any applicable combination of these factors;
(c) Be installed according to limitations specified for that equipment; and
(d) Function properly when installed.
And Section 23.1525, Kinds of operation.
The kinds of operation authorized (e.g., VFR, IFR, day or night) and the meteorological conditions (e.g., icing) to which the operation of the airplane is limited, or from which it is prohibited, must be established appropriate to the installed equipment.
VFR REQUIREMENTS.
A magnetic non-stabilized direction indicator is required equipment by § 23.1303 and also for VFR operation by § 91.205. The required accuracy for magnetic non-stabilized direction
144 indicator is prescribed in § 23.1327 as ±10º unless a correction card, placard, or gyroscopic direction indicator is used. If the sole purpose of the gyroscopic direction indication is for backing up the magnetic non-stabilized direction indicator, then the accuracy of displayed headings can also be to ±10º. This should not be interpreted as the required accuracy for the gyroscopic direction indicator in general.
IFR REQUIREMENTS.
For IFR, a gyroscopic direction indication is required by § 91.205. The gyroscopic direction indicator should meet the TSO-C5d or TSO-C6c or equivalent. A Direction Instrument, Magnetic (Gyroscopically Stabilized) should meet the minimum performance standard of TSO- C6d. As with most TSO's, TSO-C6d refers to SAE documents AS 8013 for the minimum performance standards. In this document, the standard in paragraph 4.4, Turn Error, is “Two minutes after resumption of straight and level flight the scale error resulting from coordinated turn of 180º in 1 minute at a true airspeed of 180 miles per hour (289 km/h) shall be within 2º.”
During stabilized and under environmental conditions, the test requirement for the error tolerance is 2º.
The TSO is an equipment minimum performance standard and not an installation standard. For the TSO qualification, the equipment is tested under extreme environmental conditions and they should be compatible for this airplane installation.
See AC 23-8A, Flight Test Guide for Certification of Part 23 Airplanes, for additional guidance.