7. Can the applicant assume an emergency descent?
For answer 1, the smoke must obscure the panel. An emergency descent cannot be started until the smoke evacuation takes effect.
Amendment 23-42 and Subsequent
This amendment makes § 23.831(b) and the policy under Amendments 23-34 and subsequent applicable to all part 23 pressurized airplanes, not just commuter category.
AC 25-9A, “Smoke Detection, Penetration, and Evacuation Tests and Related Flight Manual Emergency Procedures,” dated January 6, 1994, provides an acceptable means of compliance for the smoke evacuation requirements of this section.
Amendment 23-62 and Subsequent
In Docket No. FAA-2009-0738, the Discussion of the Regulatory Amendments stated: The FAA amended § 23.831 to add new paragraphs §§ 23.831(c) and (d), which include standards appropriate for airplanes operating at high altitudes beyond those included in part 23. The changes are intended to ensure flight deck and cabin environments do not result in the crew’s mental errors or physical exhaustion that would prevent the crew from successfully completing assigned tasks for continued safe flight and landing. An applicant may demonstrate compliance with § 23.831(d) of this requirement if the applicant can show that the flight deck crew’s performance is not degraded.
The cabin environment must be conservatively specified such that no occupant would incur any permanent physiological harm after a depressurization. The environmental and physiological performance limits used for demonstrating compliance must originate from recognized and cognizant authorities as accepted by the regulatory authority reviewing the compliance finding.
As part of the certification process, the FAA considers the entire flight profile of the airplane during the depressurization event. The profile includes cruise and transient conditions during descent, approach, landing, and rollout to a stop on the runway.
The FAA does not include taxiing as a compliance consideration because the airplane would be on the ground and could be evacuated, or flight deck windows and cabin doors could be opened for ventilation. The condition of the airplane from the beginning of the event to the end of the landing roll is accounted for when assessing the safe exit of an airplane.
The FAA chose the words “… shall not adversely affect crew performance …” to mean the crew can be expected to reliably perform either their published or trained duties, or both, to complete a safe flight and landing. The FAA has measured this in the past by a person’s ability to track and perform tasks. The event should not result
Change 1 AC 23-17C 7/16/2012
138 in expecting the crew to perform tasks beyond the procedures defined by the manufacturer or required by existing regulations. The FAA uses the phrase “No occupant shall sustain permanent physiological harm” to mean the occupants who may have required some form of assistance, once treated, must be expected to return to their normal activities.
To show compliance to the proposed rule, the applicant must consider what happens to the airplane and systems during depressurization. The applicant may also consider operational provisions, which provide for or mitigate the resulting environmental effects to airplane occupants. If the manufacturer provides an approved procedure(s) for depressurization, the flight deck and cabin crew may configure the airplane to moderate either temperature or humidity extremes, or both, on the flight deck and in the cabin. This configuration may include turning off non-critical electrical equipment and opening the flight deck door or opening the flight deck window(s).
This amendment applies ventilation rules in new § 23.831(c) and (d) to all jet powered pressurized airplanes with any service ceiling.
The Final Rule is intended to apply to flight above 41,000 feet. The final rule for paragraphs § 23.831(c) and (d) is changed to state the paragraphs are applicable only for the cruise phase of flight above 41,000 feet. The intent is for airplanes that operate above 41,000 feet, and the FAA is not aware of any turboprop or piston engine airplanes that operate above 41,000 feet. Special conditions would be applied to a turboprop or piston airplane with a maximum service ceiling above 41,000 feet.
Section 23.831 is modified as discussed.
139 Section 5. Pressurization
23.841 Pressurized cabins
The corresponding rules in CAR 3 are CAR 3.394 and 3.395.
There is no corresponding airworthiness criteria in the Airship Design Criteria.
Original Issue and Subsequent
§ 23.841(c) requires there be a means to rapidly equalize the pressure differential.
Assuming isothermal conditions, the time for the pressures to equalize depends on the cabin volume, the effective area of the safety-dump valves, the cabin inflow, and the pressures inside and outside the cabin. If the size of the effective area of the valve is small in comparison to the cabin volume, the rate of pressure change may be too slow to equalize the pressures before an adverse event could occur. The time period to rapidly equalize the pressures should consider maximum certificated cabin pressure differential, operation of the pressurization system, and either operation of the emergency exits or the cabin entrance doors, or both. When landing the airplane under emergency conditions, the safety-dump valve should have sufficient flow capacity to rapidly equalize the cabin pressure within a time period so the cabin doors and emergency exits can be opened and evacuation is not impaired. Time to equalize the ambient and cabin pressures should be shown. Inflatable door seals, if installed, are subject to the requirements of this rule.
§ 23.841(f) requires a warning device for safe or preset pressure differential and absolute cabin pressure. A warning is interpreted to suggest the need for an immediate corrective action, so it may not operate unless there is a failure, and the visual indication should be red per § 23.1322. Red lines on altimeters or pressure indicators are used to indicate operating limits, but they are not acceptable warning means.
Amendment 23-7 and Subsequent This amendment changed the warning requirements in § 23.841(f). The explanation in NPRM 67-14 states as follows: “Present Sec. 23.841 (f) does not describe what pressure warning devices are acceptable. This proposal would follow the approach of Sec. 25.841 (b) (6), that is, that instrument markings are sufficient for safe warning of pressure differential limits, whereas aural or visual means are necessary for safe warning of absolute pressure limits.” The Final Rule, Docket 8083, added the following: “The proposed requirement permits the use of markings on the presently required pressure differential indicator as the warning indicator.”
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