140 Amendment 23-14 and Subsequent
This amendment requires that cabin pressure altitude not exceed 15,000 feet in any probable failure for airplanes certificated to operate over 31,000 feet. It is not proper to use an emergency descent procedure to show compliance to this rule when compliance can be achieved through design. The Emergency Operations Section of the AFM should include an emergency descent procedure for use in a rapid decompression from any failure not withstanding the likelihood of its occurrence.
Amendment 23-17 and Subsequent A proposed revision in NPRM 75-10 explains Amendment 23-17 as follows: “This proposal would make clear that the rule applies to cabin pressure and the rate of change of cabin pressure. The proposal would also conform the rule to current practice, which is to provide a warning when the cabin pressure altitude exceeds 10,000 feet. This amendment established 10,000 feet as the maximum absolute cabin pressure for operation of the pressure altitude warning. Therefore, the pressure sensors used in the warning system cannot have an operating set point and tolerance that would prevent the warning from being given at or before 10,000 feet. A feature that automatically changes the warning altitude to 15,000 feet for operations at field elevations above 10,000 feet is acceptable to prevent nuisance warnings.”
The following material is a means of compliance to § 23.841(b)(3) that requires a means by which the pressure differential can be rapidly equalized. Section
23.841(b)(6) offers a provision for a warning indication at the pilot station to indicate when a cabin pressure altitude of 10,000 feet is exceeded.
1. RELATED 14 CFR PART 23 SECTIONS . These acceptable means of compliance refer to certain provisions of part 23 and the corresponding provisions of part 3 of the CAR for airplanes for which those regulations are applicable.
Listed below are the applicable and the related part 23 sections with the corresponding CAR sections shown in parenthesis:
a. § 23.365 (3.197)
b. § 23.775(c) (3.383)
c. § 23.841 (3.395)
d. § 23.843 (3.396)
2. DISCUSSION OF REQUIREMENTS . In discussing these requirements, a brief history on the development of the applicable airworthiness regulations is first presented. The purpose of the airworthiness requirements for small airplanes is then explained.
a. Rapidly Equalizing the Pressure
(1) History. The requirement for a means by which the pressure differential can be rapidly equalized was introduced in the airworthiness regulations for pressurized cabins for transport category airplanes when part 04 of the CAR became effective on November 9, 1945. Because of the trend to develop pressurized cabins for small airplanes, the 1956 Annual Airworthiness Review established similar requirements for pressurized cabins for small airplanes. The criteria were developed by using the principles that were applicable to pressurized cabins on transport category airplanes. This was because most of the cabin pressure control system design for small airplanes drew heavily on the equipment designed and developed for transport category airplanes. As a result, many of the provisions added to part 3 of the CAR by Amendment 3-2, effective August 12, 1957, were substantially the same as those which applied to transport category airplanes. Under the recodification program in 1965, part 23 replaced part 3 of the CAR and these requirements are now in § 23.841(b)(3).
(2) The purpose of this requirement is to provide the crew with a means to rapidly equalize the differential pressure to permit quick opening of the emergency exits and entry door(s) for a gear up landing under emergency conditions. This means may be used for other events such as over pressurization and reducing cabin contamination. These functions are described in further detail as follows:
(a) Because of a malfunction in the pressurization system or abnormal operational conditions, the cabin pressure is above normal conditions during the airplane-landing phase. In this case, the cabin pressure may be vented by the safety-dump valve operated through a manual controller or triggered by the landing gear safety switch so the emergency exits and the cabin entrance doors could be opened.
(b) If a failure such as a cracked wi ndow or windshield occurs, the cabin pressure should be capable of being rapidly reduced so the loads because of cabin pressure differential can be reduced accordingly.
(c) When a threatening cabin overpre ssure condition exists because of cabin pressurization system malfunction, the cabin pressure can be reduced by the safety-dump valve to prevent a structural failure of the pressure vessel.
(d) When the cabin air becomes contaminated by smoke and fumes, the cabin safety-dump valve may be used, depending on the conditions to assist the pressurization or ventilation system, or both, in evacuation of the cabin air to reduce the contaminants.
b. Cabin Pressure Altitude Warning
(1) History
(a) The cabin altitude warning and many of the provisions for pressurized cabins for small airplanes were added to part 3 of the CAR by Amendment 3-2, effective August 12, 1957. Section
3.395(f) of part 3 of the CAR required, in relevant part, the pilot be provided a warning when safe or preset limits on pressure differential and on absolute cabin pressure were exceeded.
(b) In May 1958, a quantitative requi rement was introduced in the airworthiness regulations when FAA established policy for altitude warning on the sport category airplanes. This policy, which was set forth in § 4b.375-l of CAR part 3, required the warning for cabin pressure would meet the applicable requirements if it occurred when cabin absolute pressure was reduced below that equivalent to 10,000 feet. Under the recodification program in 1965, part 25 replaced part 4b of the CAR and the 10,000 feet warning policy was carried over as an appropriate means of meeting the warning requirements in § 25.841.
(c) As part of the First Biennial Airworthiness Review Program in 1975, Amendments 23-17 and 25-28, which changed parts 23 and 25 respectively, were issued and became effective February 1, 1977.
Amendment 25-28 transmitted a minor change to § 25.841 as follows: It changed "cabin absolute pressure is below that equivalent to 10,000 feet" to "cabin pressure altitude exceeds 10,000 feet."
Amendment 23-17 brought into § 23.841 of part 23 a warning indication when the cabin pressure altitude of 10,000 feet MSL is exceeded. The preamble for this change indicated this proposal was adopted because most small airplanes had such a warning and many pilots had begun to rely on this warning.
(2) The purpose of the cabin pressure al titude-warning requirement is to indicate a warning at the pilot station when the cabin pressure altitude is greater than 10,000 feet MSL. A possible hazardous condition could be when the airplane reaches the operating altitude, which is greater than 10,000 feet MSL, and a malfunction in the cabin pressurization system occurs. If there was no warning for cabin pressure altitude, the cabin pressure altitude could slowly increase undetected to the airplane altitude, and the crew and passengers could become unconscious because of hypoxia. The effects of hypoxia are usually encountered when the flight crew is exposed to altitudes above 10,000 feet during extended flights.
3. Acceptable Means of Compliance
Warnings and Cautions. Section 23.1322 provides specific requirements for assigning red and amber for visual indications. Specifically, for abnormal operational or airplane systems conditions, a "caution" should be generated for crew awareness and subsequent crew action may be required; the associated color is amber. Under emergency operational or airplane systems conditions, a “warning” should be generated for immediate crew recognition and when corrective or compensatory action may be required; the associated color is red. If the cabin pressure altitude warning is a visual indicator, it should be red to indicate a hazard.
Air Conditioning System R12 to R134 conversion
Because an unsafe condition could occur, direct conversion without certification is not possible due to the characteristics of the refrigerants. Incompatibilities can include o-rings, gaskets, washers, receiver-dryers, expansion valves, and hoses. The system oil must also be changed, so a flush is required.
Amendment 23-49 and Subsequent
This amendment changed the 33,000 feet in § 23.841(a) to 25,000 feet based on European Joint Aviation Requirements Proposals.
Amendment 23-62 and Subsequent
In Docket No. FAA-2009-0738, the Discussion of the Regulatory Amendments stated:
FAA found it necessary to amend the standards in § 23.841 to prevent exposure of the occupants to cabin pressure altitudes that could keep the flight crew from safely flying and landing the airplane or cause permanent physiological injury to the occupants.
The intent of the changes to § 23.841 is to provide airworthiness standards that allow subsonic, pressurized jets to operate at their maximum achievable altitudes—the highest altitude an applicant can choose to demonstrate the effects to several occupant related items after decompression. The applicant must show that: (1) the flight crew would remain alert and be able to fly the airplane, (2) the cabin occupants would be protected from the effects of hypoxia (i.e., deprivation of adequate oxygen supply), and (3) if some occupants do not receive supplemental oxygen, they would be protected against permanent physiological harm.
Existing rules require the cabin pressure control system maintain a cabin altitude of not more than 15,000 feet if any probable failure or malfunction in the pressurization system occurs. Cabin pressure control systems on part 23 airplanes frequently exhibit a slight overshoot above 15,000 feet cabin altitude before stabilizing below 15,000 feet. Existing technology for cabin pressure control systems on part 23 airplanes cannot prevent this momentary overshoot, which prevents strict compliance with the rule. FAA has granted findings of ELOS for this characteristic because physiological
144 data shows the brief duration of the overshoot has no significant effect on an airplane’s occupants.
Special conditions issued for part 23 jets are similar and, for operating altitudes above 41,000 feet, equivalent to the requirements in § 25.841 adopted in Amendment 25-87 (61 FR 28684). That Part 25 amendment revised § 25.841(a) to include requirements for pressurized cabins that were previously covered only in special conditions. The special conditions required consideration of specific failures. The FAA incorporated reliability, probability, and damage tolerance concepts addressing other failures and methods of analysis into part 25 after the issuance of the special conditions. The Small Airplane Directorate requires the use of these additional methods of analysis as part of this rulemaking.
This proposal also specifies a more performance-based criterion such that failures cannot adversely affect crew performance nor result in permanent physiological harm to passengers.
NOTE: It is a different standard for the crew than the passengers.
Part 23 requires a warning of excessive cabin altitude at 10,000 feet. Those regulations do not adequately address airfield operation above 10,000 feet. Rather than disable the cabin altitude warning to prevent nuisance warnings, FAA has issued ELOS findings that allow the warning altitude setting to be shifted above the maximum approved field elevation, not to exceed 15,000 feet. FAA proposes to revise § 23.841to incorporate language from existing ELOSs into the regulation.
This amendment made several changes:
1. § 23.841(a) was changed to permit an overshoot above 15,000 feet cabin altitude for 10 seconds or less following a decompression from a probable failure of the pressurization system. The overshoot cannot exceed 25, 000 feet. This eliminates the need for an equivalent level of safety.
2. § 23.841(b)(6) was changed the warning indi cation to allow it to occur up to 15,000 feet for high altitude operations, which removes the need for an equivalent level of safety.
3. §§ 32.841(c), (d) and (e) were added to im pose high altitude rules for any Part 23 airplane with a service ceiling above 41,000 feet and not more than 45,000 feet. These new rules remove the need for high altitude special conditions.
The Final Rule substantially changed the NPRM. The FAA changed §
23.841(b)(6)(ii) to permit a single operation for high altitude takeoffs and landings. §
23.841(c)(2) is changed to exclude extremely improbable failures. The Level of Validity and the full scale cyclic test requirements are deleted. Proposed § 23.841(e)
145 was deleted and the damage tolerance requirement is moved to Section 23.571.
Section 23.841 is modified as discussed.
23.843 Pressurization tests
Original Issue and Subsequent
The corresponding rule in CAR 3 is CAR 3.396.
There is no corresponding airworthiness criteria in the Airship Design Criteria.
This rule applies to all doors. This includes doors that open outward, doors that open inward and emergency exits.
The 1.5 safety factor in § 23.303 does not apply when executing the pressurization tests in this section. § 23.843(a) of the rule specifies the pressure differential of § 23.365(d), which is 1.33 times the maximum relief valve setting. § 23.843(b) requires functional testing to verify operation so there cannot be any gross plastic deformation from the 1.33 factor.
147 Section 6. Fire Protection
23.851 Fire extinguishers
The corresponding rule in CAR 3 is CAR 3.388.
The corresponding airworthiness criteria is section 4.39, Airship Design Criteria, FAA-P-8110-2, Change 2.
Amendment 23-34 and Subsequent
A proposed revision in NPRM 83-17 lists the source for Amendment 23-34 as SFAR 41, sections 7(d) and (e).
See AC 20-42D, “Hand Fire Extinguishers for Use in Aircraft,” for guidance.
European Aviation Safety Agency (EASA) effective November 13, 2003, AMC
23.851(c) accepts the AC as an AMC pending research into Halon replacement.
Amendment 23-45 and Subsequent
A proposed revision in NPRM 90-18 explains this amendment as follows: “This proposal extends the commuter category requirement for a hand fire extinguisher in the pilot compartment to all small airplane categories. Additionally, this proposal provides minimum acceptable standards for on-board hand fire extinguishers.”
“Besides this specific rule for fire extinguishers, there are other rules including § 23.561, Emergency Landing Conditions (extinguishers cannot be a missile in an emergency landing); § 23.303, Factor of safety; § 23.601, Design and Construction, General; § 23.603, Materials and workmanship; and § 23.613, Material strength properties and design values. You will need to contact an Aircraft Certification Office for an installation in a small airplane.”
23.853 Passenger and crew compartment interiors
The corresponding rule in CAR 3 is CAR 3.388.
The corresponding airworthiness criteria is section 4.39, Airship Design Criteria, FAA-P-8110-2, Change 2.
See AC 21-4B, Special Flight Permits for Operation of Overweight Aircraft, for flammability issues in ferry fuel tanks.
Original Issue and Subsequent
See AC 23-2A, “Flammability Tests.”
The purpose of this policy is for standardization in the approval of flammability testing of materials used in small airplanes per 14 CFR part 23, §§ 23.853, 23.855, and 23.1359.
The Small Airplane Directorate policy for all certification projects, including engineering assistance for major alterations on FAA Form 337, Field Approvals, is as follows:
a. The only materials for which flammability testing is not required are those that would not contribute significantly to propagating a fire per 14 CFR, part 23, § 23.853. These materials/parts are typically small parts. Material certification by an applicant or their supplier can be used in the determination the material will not significantly contribute to propagating the fire.
Company/supplier material certifications cannot be used instead of official FAA flammability testing.
1. Materials/parts of metallic construction other than magnesium are able to meet the flame-resistant requirement for normal, utility, and acrobatic aircraft as well as the self-extinguishing requirement for commuter aircraft without testing.
2. Instruments with metallic cases other than magnesium can be approved without flammability testing based on the ability of the case to contain fire/sparks until the circuit protection device removes power to the instrument.
b. All other proposed materials must be tested to the flammability level required by the certification basis and category of airplane. AC 23-2A, “Flammability Tests,” gives guidance on conducting flash-resistant, flame-resistant, fire-resistant, fireproof, and self-extinguishing tests. The AC specifies that Appendix F of part 23 be used for proposed self-extinguishing materials. These are official FAA certification tests, which require witnessing by either an FAA certification
149 engineer or an FAA Flammability DER who has authorization to witness a test.
FAA will also accept from a DER submittal of an FAA Form 8110-3 that certifies to the validity of the data being approved. This can occur when the people running the test are well known to the DER and judged by the DER to be technically competent and reliable. Test data may only be approved by the FAA or by a DER with that approval authority.
NOTE: DOT/FAA/AR-00/12, “Aircraft Materials Fire Test Handbook” is acceptable for Part 23 compliance.
c. A DER should not use FAA Form 8110-3 for flammability test results for a material when the testing is for quality assurance purposes for either a manufacturer or a repair station. Testing done for these purposes should be documented in a quality assurance report. When the material supports a certification project or an alteration or repair, FAA Form 8110-3 is the DERs only means of approving the technical data. The DER should determine if the testing documented in the test report adequately addresses the applicable airworthiness standards for the intended use of the material. If found acceptable, the DER may generate an FAA Form 8110-3 that references the test report. For flammability testing, this technical data includes records of preconditioning of the test specimen. The flammability testing required by the certification basis is as follows:
Passenger and Crew Compartment Interiors, § 23.853
Certification Basis Category Material Flammability Testing
CAR 3 Normal Flame resistant if smoking allowed (1945-1946) Restricted Effective Experimental November 13, 1945
CAR 3 Normal, Flash resistant (1946-1949) Utility and Effective Acrobatic December 15, 1946
CAR 3 Normal, Flash resistant or flame resistant if (1949-1965) Utility and smoking is allowed in a specific Effective Acrobatic compartment November 1, 1949
150 Certification Basis Category Material Flammability Testing
Part 23 Normal, Flame resistant Through Utility and Amendment 23-22 Acrobatic (1965-1978) Effective December 5, 1978
Part 23 (78-present) Normal, Flame resistant or selfextinguishing
Amendment 23-23 Utility and pe r Appendix F for materials and Subs located Acrobatic on the cabin side of the firewall and Subsequent (1978-present) Effective December 1, 1978
Part 23 Commuter Self-ex tinguishing per Appendix F Amendment 23-34 except for small parts in and Subsequent § 23.853(d)(3)(v) (1987-present) Effective February 17, 1987
Cargo and Baggage Compartment Fire Protection, § 23.855
Part 23 Normal, Meet provisions of § 23.853(d)(3) Amendment 23-49 Utility and (1996-present) Acrobatic Effective March 11, 1996
Part 23 Commuter Meet provisions of § 23.853(d)(3) Amendment 23-49 (1996-present) Effective March 11, 1996
151 Certification Basis Category Material Flammability Testing
Electrical System Fire Protection, § 23.1359
Part 23 (96-present) Normal, Meet provisions of § 23.863 and Amendment 23-49 Utility, § 23.1182 and wire insulation self Effective Acrobatic and extinguishing per Appendix F, March 11, 1996 Commuter 60-degree angle test
1. Per AC 23-2A, cloth, wire and sheet sp ecimens may be taken from a sample segment (batch/roll/sheet). In this case, FAA conformed test specimens/parts per 14 CFR, part 21, § 21.33, are not required. Instead, conformity can be established for these types of materials based on bill of materials and roll identification. The FAA Form 8110-3 should state it applies to the specific batch/roll/sheet for which the test was conducted.
NOTE: Wire specified in AC 43-13-1B, section 7, has been determined to be acceptable for use in certified airplanes and may be used without flammability testing.
2. In other cases, test specimens must be fabricated to accurately represent the installation configuration or must be cut from parts. These parts should be conformed per 14 CFR, part 21, § 21.33, before testing.
3. In both 1 and 2 above, a DER mu st comply with Order 8110.37D, “Designated Engineering Representative (DER) Handbook.” While FAA understands that in the past some DERs have not always submitted FAA Forms 8110-3 with make and model information, FAA Forms 8110-3 must always be complete, including the make and model information.
d. Flammability requirements have not b een applied to conventional aircraft structure. However, the use of composite structure can result in a need to test a representative build-up panel with an interior material, adhesive and composite structure, unless it is shown the interior material does not allow an ignition source to penetrate it.
e. Interior flammability tests may be required with build-up samples. Experience has shown the thin exposed layer can burn away and expose the adhesive layer, which often is flammable and would contribute significantly to propagating a fire.
Testing only the exposed layer without the adhesive backing would not be representative. Adhesives with a flame-retardant additive should be encouraged and listed; known flammable adhesives should not be used.
f. FAA has reviewed the test criteria of part 25, Appendix F, part I, and have determined that parts/materials tested to the part 25 test criteria are acceptable data to show compliance with the flame-resistant material requirement of