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Section 3. PERSONNEL AND CARGO ACCOMMODATIONS
15. SECTION 25.773 - PILOT COMPARTMENT VIEW.
a. Rule Text.
(a) Nonprecipitation conditions. For nonprecipitation conditions, the following apply:
(1) Each pilot compartment must be arranged to give the pilots a sufficiently extensive, clear, and undistorted view, to enable them to safely perform any maneuvers within the operating limitations of the airplane, including taxiing, takeoff, approach, and landing.
(2) Each pilot compartment must be free of glare and reflection that could interfere with the normal duties of the minimum flight crew (established under § 25.1523). This must be shown in day and night flight tests under nonprecipitation conditions.
(b) Precipitation conditions. For precipitation conditions, the following apply:
(1) The airplane must have a means to maintain a clear portion of the windshield, during precipitation conditions, sufficient for both pilots to have a sufficiently extensive view along the flight path in normal flight attitudes of the airplane. This means must be designed to function, without continuous attention on the part of the crew, in −
(i) Heavy rain at speeds up to 1.6 VS1 with lift and drag devices retracted; and
(ii) The icing conditions specified in § 25.1419 if certification with ice protection provisions is requested.
(2) The first pilot must have −
(i) A window that is openable under the conditions prescribed in paragraph (b)(1) of this section when the cabin is not pressurized, provides the view specified in that paragraph, and gives sufficient protection from the elements against impairment of the pilot's vision; or
(ii) An alternate means to maintain a clear view under the conditions specified in paragraph (b)(1) of this section, considering the probable damage due to a severe hail encounter.
(c) Internal windshield and window fogging. The airplane must have a means to prevent fogging of the internal portions of the windshield and window panels over an area which would provide the visibility specified in paragraph (a) of this section under all internal and external ambient conditions, including precipitation conditions, in which the airplane is intended to be operated.
(d) Fixed markers or other guides must be installed at each pilot station to enable the pilots to position themselves in their seats for an optimum combination of 59
outside visibility and instrument scan. If lighted markers or guides are used they must comply with the requirements specified in § 25.1381.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, Apr. 8, 1970; Amdt. 25-46, Oct. 30, 1978; Amdt. 25-72, Jul. 20, 1990]
b. Intent of rule. The intent of this rule is for the flight deck windshield to provide sufficient external vision to permit the pilot to safely perform any maneuvers within the operating limits of the aircraft and, at the same time afford an unobstructed view of the flight instruments and other critical components and displays from the same eye position.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). Section 4b.351 of the CAR became § 25.773 of 14 CFR for pilot compartment view.
(1) Amendment 25-23 (April 8, 1970) added a new § 25.773(c) to require means to prevent fogging of the internal portions of the windshield and window panels which can occur under certain temperature and humidity conditions and create a hazardous situation.
(2) Amendment 25-46 (October 30, 1978) added a new § 25.773(d) requiring means (such as fixed markers) to guide the pilot to determine an optimum seat position for proper visibility.
(3) Amendment 25-72 (July 20, 1990) revised § 25.773(b)(1)(i) for clarity and consistency with actual certification practice by specifying that all lift and drag devices, e.g., slats and spoilers as well as flaps, must be retracted. In addition, section 25.773(b)(2) was revised to allow alternate means of compliance to maintain clear vision as opposed to an openable sliding window being the only means.
(4) Harmonization. Parts of this regulation (§ 25.773(b)(2) and (b)(4)) will be the subject of a Federal Aviation Regulations/Joint Aviation Requirements (FAR/JAR) harmonization effort under the Aviation Rulemaking Advisory Committee (ARAC). The ARAC harmonization working group may adopt parts of both FAR and JAR as well as revise AC 25.783-1.
d. Policy/Compliance Methods. For guidance with this requirement, refer to the preamble of this rule and Advisory Circular (AC) 25-7A, Flight Test Guide for Certification of Transport Category Airplanes, and AC 25.773-1, Pilot Compartment View for Transport Category Airplanes.
e. References. None.
16 - 25. [RESERVED]
26. SECTION 25.783 - DOORS.
a. Rule Text.
(a) Each cabin must have at least one easily accessible external door.
(b) There must be a means to lock and safeguard each external door against opening in flight (either inadvertently by persons or as a result of mechanical failure or failure of a single structural element either during or after closure).
Each external door must be openable from both the inside and the outside, even though persons may be crowded against the door on the inside of the airplane.
Inward opening doors may be used if there are means to prevent occupants from crowding against the door to an extent that would interfere with the opening of the door. The means of opening must be simple and obvious and must be arranged and marked so that it can be readily located and operated, even in darkness. Auxiliary locking devices may be used.
(c) Each external door must be reasonably free from jamming as a result of fuselage deformation in a minor crash.
(d) Each external door must be located where persons using them will not be endangered by the propellers when appropriate operating procedures are used.
(e) There must be a provision for direct visual inspection of the locking mechanism to determine if external doors, for which the initial opening movement is not inward (including passenger, crew, service, and cargo doors), are fully closed and locked. The provision must be discernible under operational lighting conditions by appropriate crewmembers using a flashlight or equivalent lighting source. In addition, there must be a visual warning means to signal the appropriate flight crewmembers if any external door is not fully closed and locked. The means must be designed such that any failure or combination of failures that would result in an erroneous closed and locked indication is improbable for doors for which the initial opening movement is not inward.
(f) External doors must have provisions to prevent the initiation of pressurization of the airplane to an unsafe level if the door is not fully closed and locked. In addition, it must be shown by safety analysis that inadvertent opening is extremely improbable.
(g) Cargo and service doors not suitable for use as emergency exits need only meet paragraphs (e) and (f) of this section and be safeguarded against opening in flight as a result of mechanical failure or failure of a single structural element.
(h) Each passenger entry door in the side of the fuselage must meet the applicable requirements of §§ 25.807 through 25.813 for a Type II or larger passenger emergency exit.
(i) If an integral stair is installed in a passenger entry door that is qualified as a passenger emergency exit, the stair must be designed so that under the following conditions the effectiveness of passenger emergency egress will not be impaired:
(1) The door, integral stair, and operating mechanism have been subjected to the inertia forces specified in 25.561(b)(3), acting separately relative to the surrounding structure.
(2) The airplane is in the normal ground attitude and in each of the attitudes corresponding to collapse of one or more legs of the landing gear.
(j) All lavatory doors must be designed to preclude anyone from becoming trapped inside the lavatory, and if a locking mechanism is installed, it be capable of being unlocked from the outside without the aid of special tools.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-15, 32 FR 13262, Sep. 20, 1967; Amdt. 23-23, 35 FR 5676, Apr. 8, 1970; Amdt. 25- 54, 45 FR 60173, Sep. 11, 1980; Amdt. 25-72, 55 FR 29780, Jul. 20, 1990; Amdt.
25-88, 61 FR 57956, Nov. 8, 1996]
b. Intent of Rule. The intent of the term "reasonably free" is to provide proper dimensional clearances around door structure and seals. The requirement is also defined under § 25.809(g):
"There must be provisions to minimize the probability of jamming of the emergency exits resulting from fuselage deformation in a minor crash landing."
c. Background. This regulation is the subject of a Federal Aviation Regulations/Joint Aviation Requirements (FAR/JAR) harmonization effort under the Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group is tasked to recommend revisions to § 25.783 and related crashworthiness regulations and to recommend revisions to AC 25.783-1A.
d. Policy/ComplianceMethods. For policy and guidance on compliance with this requirement, refer to Advisory Circular (AC) 25-783-1, Fuselage Doors, Hatches, and Exits;
AC-25-21, Certification of Transport Airplane Structure, paragraph 85; and AC 25-17A, Transport Airplane Cabin Interiors Crashworthiness Handbook.
e. Reference. None.
27 - 29. [RESERVED]
Section 4. VENTILATION AND HEATING
36. SECTION 25.831 - VENTILATION.
a. Rule Text.
(a) Under normal operating conditions and in the event of any probable failure conditions of any system which would adversely affect the ventilating air, the ventilation system must be designed to provide a sufficient amount of uncontaminated air to enable the crewmembers to perform their duties without undue discomfort or fatigue and to provide reasonable passenger comfort. For normal operating conditions, the ventilation system must be designed to provide each occupant with an airflow containing at least
0.55 pounds of fresh air per minute.
(b) Crew and passenger compartment air must be free from harmful or hazardous concentrations of gases or vapors. In meeting this requirement, the following apply:
(1) Carbon monoxide concentrations in excess of 1 part in 20,000 parts of air are considered hazardous. For test purposes, any acceptable carbon monoxide detection method may be used.
(2) Carbon dioxide concentration during flight must be shown not to exceed 0.5 percent by volume (sea level equivalent) in compartments normally occupied by passengers or crewmembers.
(c) There must be provisions made to ensure that the conditions prescribed in paragraph
(b) of this section are met after reasonably probable failures or malfunctioning of the ventilating, heating, pressurization, or other systems and equipment.
(d) If accumulation of hazardous quantities of smoke in the cockpit area is reasonably probable, smoke evacuation must be readily accomplished, starting with full pressurization and without depressurizing beyond safe limits.
(e) Except as provided in paragraph (f) of this section, means must be provided to enable the occupants of the following compartments and areas to control the temperature and quantity of ventilating air supplied to their compartment or area independently of the temperature and quantity of air supplied to other compartments and areas:
(1) The flight crew compartment.
(2) Crewmember compartments and areas other than the flight crew compartment unless the crewmember compartment or area is ventilated by air interchange with other compartments or areas under all operating conditions.
(f) Means to enable the flight crew to control the temperature and quantity of ventilating air supplied to the flight crew compartment independently of the temperature and quantity of ventilating air supplied to other compartments are not required if all of the following conditions are met:
(1) The total volume of the flight crew and passenger compartments is 800 cubic feet or less.
(2) The air inlets and passages for air to flow between flight crew and passenger compartments are arranged to provide compartment temperatures within 5 degrees F. of each other and adequate ventilation to occupants in both compartments.
(3) The temperature and ventilation controls are accessible to the flight crew.
(g) The exposure time at any given temperature must not exceed the values shown in the following graph after any improbable failure condition.
temperature curve from Amdt. 25-87
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-41, 42 FR 36970, Jul. 18, 1977; Amdt. 25-87, 61 FR 28695, Jun. 5, 1996; Amdt. 25- 89, 61 FR 63956, Dec. 2, 1996]
b. Intent of Rule. The intent of this rule is to supply passengers and crewmembers with enough uncontaminated air to provide reasonable comfort during normal operating conditions and also after any probable failure of any system that would adversely affect the cockpit or cabin ventilation air.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The majority of the requirements from section 4b.371 of the CAR were carried over directly to § 25.831 of 14 CFR for ventilation.
(1) Amendment 25-41 (July 18, 1977) revised the rule to clarify the requirements for the means by which crewmembers can control the temperature and quantity of ventilating air in the flight crew compartment and compartments occupied by other crew members.
(2) Amendment 25-87 (June 5, 1996) revised the rule to codify special conditions that had been used to certify certain airplanes for high altitude operation (maximum altitudes up to 64
45,000 or 51,000 feet). The amendment added the requirement that each occupant be provided with 0.55 pounds (equivalent to 10 cubic feet) per minute of fresh air, reference § 25.831(a).
The amendment also specifies limits for interior temperatures after specific failures, reference § 25.831(g). Compliance to Amendment 25-87 is required for only those airplanes whose certification basis includes this amendment. Most of the airplanes that are currently produced do not fall into this category. An accompanying advisory circular, AC 25-20, Pressurization, Ventilation, and Oxygen Systems Assessment for Subsonic Flight including High Altitude Operation, was also issued to provide one means, but not the only means, of compliance to the regulations affected by Amendment 25-87.
(3) Harmonization. This regulation is the subject of a Federal Aviation Regulations/Joint Aviation Requirements (FAR/JAR) harmonization effort under the Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group will be tasked to recommend revisions to §§ 25.831, 25.841, and related regulations and to recommend revisions to AC 25.20.
(4) Amendment 25-89 (December 2, 1996) revised § 25.831(b)(2) to change the carbon dioxide requirements from three percent by volume to 0.5 percent by volume (sea level equivalent). The following information is extracted from an FAA letter dated May 18, 1999, to the Society of Automotive Engineers (SAE) Committee AC-9, Aircraft Environmental Systems, to acknowledge an error in the preamble to Amendment 25-89, page P-610, 3rd paragraph. It states that ". . . sea level equivalent (SLE) for a cabin altitude of 8,000 feet would be 0.5 percent multiplied by 0.74 . . ." The word "multiplied" should have read "divided." The FAA does not feel that an increase in carbon dioxide concentration from 0.5 percent SLE to 0.68 percent at altitude will introduce an appreciable discomfort or hazard to passengers and maintains a concentration level well below industry recommendations for carbon dioxide exposure.
d. Policy/Compliance Method. For guidance on compliance with this requirement, refer to the preambles of this rule and the following information.
(1) Ventilation rates are determined by tests and/or analyses. For compliance with § 25.831(b) and (c), carbon monoxide and carbon dioxide levels may be measured with hand held samplers or gas measurement devices for the various flight conditions, such as takeoff, cruise, and landing. Measurements are made at "head" level in the cockpit, other compartments occupied by crewmembers, and in the passenger cabin.
(2) Smoke Evacuation. For compliance with § 25.831(d), cockpit smoke evacuation test methods are addressed in AC 25-9A, Smoke Detection, Penetration, and Evacuation Tests and Related Flight Manual Emergency Procedures. The AC 25-9A also provides guidance regarding lavatories, galleys, crew rest areas, equipment cooling bays, and cargo compartments smoke detection/penetration/evacuation.
(3) Ventilation System Design. The ventilation system design should be reviewed and tests or analyses conducted to ensure compliance with § 25.831(e) and (f), which address control of temperatures and ventilating air quantity in compartments occupied by crewmembers.
(4) Airplane Operation with Airconditioning Packs Off. The following policy is extracted from an FAA memorandum dated September 3, 1999, in response to questions regarding compliance with § 25.831 while operating with the airconditioning packs off.
(a) Background. The following summarizes some key elements that are necessary to understand in determining the certification policy regarding cabin ventilation, smoke detection and evacuation, and equipment cooling.
(b) The provisions of § 25.831(a), as amended by Amendment 25-41, state: “Each passenger and crew compartment must be ventilated, and each crew compartment must have enough fresh air (but not less than 10 cu. ft. per minute per crewmember) to enable crewmembers to perform their duties without undue discomfort or fatigue”.
(c) A 1983 memo addressing airconditioning packs-off operation provides additional guidance to the regulatory provisions of § 25.831(a), as amended by Amendment
25-41.
1 The memo states: “The proposed environmental control system (ECS) takeoff procedure for the Model ABC should be processed for certification by an exemption to
25.831(a).”
2 The memo also states: “Analysis and tests have been used to substantiate that operating without the required 10 cubic feet per minute per pilot (§ 25.831(a)) for short duration will not impair pilot performance or significantly affect equipment reliability. This is not to say that the pilots need be comfortable. These ECS ‘off’ approvals were made in accordance with adequate criteria, but not all were made in accordance with correct certification procedures (i.e., equivalency or exemption).”
(d) Subsequently, Amendment 25-87, effective April 30, 1998, amended several of the airworthiness provisions concerning cabin ventilation. Section 25.831(a) was changed to require that “. . . the ventilation system must be designed to provide a sufficient amount of uncontaminated air to enable the crewmembers to perform their duties without undue discomfort or fatigue and to provide reasonable passenger comfort. For normal operating conditions, the ventilation system must be designed to provide each occupant with an airflow containing at least
0.55 pounds of fresh air per minute.”
1 The preamble to Amendment 25-87 adds the following additional information. “One commenter recommends allowing the fresh air requirements proposed to be required under § 25.831(a) to remain a crewmember requirement only. The FAA does not concur with this recommendation. It has been determined that this level of airflow is required for several reasons. Members of the flightcrew performing their functions in the passenger cabin are not sedentary and must perform their duties without undue discomfort or fatigue. In addition, fresh airflow has been determined to be necessary to provide adequate smoke clearance in the event of smoke accumulation due to a system failure or fire. However, it is clear that the 66
additional airflow is not required at all times and under all operating conditions. Therefore, the wording in the final rule has been changed to state that the ventilation system must be designed to provide the fresh airflow. This also addresses concerns regarding the low fresh airflow capability that occurs during descent at low power levels.”
(e) Advisory Circular 25-20 was developed concurrent with Amendment 25-87.
Paragraph 5d states: “Takeoff with airconditioning or bleed air system ‘off’ may be an acceptable procedure provided the ventilation system continues to provide an acceptable environment in the passenger cabin and cockpit for the brief period when the ventilation system is not operating normally.”
(f) The Draft Version of this AC (dated November 30, 1998) was issued for public comment as well as coordinated for directorate comments. This AC includes a statement that recommends that the exemption process be used to approve the cabin ventilation system for operation with airconditioning packs-off operation. However, the Aerospace Industries Association (AIA) has questioned the need for an exemption and stated that the no packs takeoff procedures already exist; that as the transient for this condition is short, this is an accepted practice; and that it does not cause the cabin environment to be unsafe. In addition, the Los Angeles Aircraft Certification Office (ACO) commented that an equivalent safety finding was more appropriate than an exemption.
(g) Analysis. The Transport Standards Staff’s (TSS) interpretation of the provisions of § 25.831(a), as amended by Amendment 25-41, is that the prescribed airflow for the flightcrew is required to be provided during normal operation. However, the certification records do not show that any such equivalent safety finding or exemption for airconditioning packs-off operation (i.e., no fresh air for crewmembers) was issued for the model ABC or for any other transport category airplane. Therefore, the TSS assumes that any transport category airplane for which the AFM allows packs-off operation, does not strictly comply with the provision of § 25.831(a), as amended by Amendment 25-41.
1 Recognizing that the cabin ventilation provisions of Amendment 25-41 were overly restrictive, the FAA, in Amendment 25-87, changed the requirement of § 25.831 so that the regulatory provision now reads: “ . . . the ventilation system must be designed to provide a sufficient amount of uncontaminated air to enable the crewmembers to perform their duties without undue discomfort or fatigue . . .”
2 The preamble discussion quoted above states that the reason for this change is that “. . . it is clear that the additional airflow is not required at all times and under all operating conditions.”
3 Therefore, provisions of § 25.831, as amended by Amendment 25-87, specify a design requirement and allow for limited interruptions of the specified design airflow.
However, this interruption may not result in “undue” discomfort or fatigue to the crewmembers.
Advisory Circular (AC) 25-20, which was developed concurrently with Amendment 25-87, supports this interpretation (see excerpt above).
4 Furthermore, an airplane accident heightened FAA awareness to the need to address smoke penetration and include cargo compartment fire protection (detection and suppression) throughout the flight, including taxi, takeoff and climb. When determining compliance with the sections of part 25 relating to flight crew compartment air quality, ventilation, smoke penetration/evacuation, cargo compartment fire protection (detection and suppression) and equipment cooling, all the impacts related to operating with the airconditioning packs off for a limited time must be determined. The TSS considers the failure to document any consideration of these issues in previous compliance findings an oversight by the FAA.
5 While direct compliance to § 25.831(a), as amended by Amendment 25-87, for airconditioning packs-off operation is possible without using an equivalent safety finding; an equivalent safety finding (§ 21.21(b)(1)) may be used for showing compliance with the provisions of § 25.831(a), as amended by Amendment 25-41, for airconditioning packs-off operation.
(h) Conclusion. The TSS has determined that while direct compliance to § 25.831(a), as amended by Amendment 25-87, for airconditioning packs-off operation is possible without using an equivalent safety finding, an equivalent safety finding (§ 21.21(b)(1)) may be used for showing similar compliance with the provisions of § 25.831(a), as amended by Amendment 25-41. The equivalent safety finding must document that the ventilation system continues to provide an acceptable environment in the passenger cabin and cockpit for the brief period when the ventilation system is not operating normally. The degradation of crewmember air quality must not reach the level that would cause undue discomfort and fatigue to the point that it could affect the performance of their duties.
(i) Advisory Circular (AC) 25.1581-1, Airplane Flight Manual, issued in 1997, states in paragraph 2b(11), Systems and Equipment Limitations, that; “all limitations applicable to systems and equipment installations that are considered necessary for safe operation must be included.” Airconditioning packs-off operation is intended to be a short duration operation.
Therefore, the maximum period of operation in this configuration should be defined by the applicant and specified in the AFM, along with any related operating procedures necessary to maintain compliance with the regulatory issues discussed above. An example of establishing "the maximum period of operation (short duration) for takeoff" would be an operational phase beginning with turning packs off when cleared into position for takeoff, and ending when packs were turned back on after takeoff thrust was reduced to climb thrust or when accomplishing the "after-takeoff" checklist.
(j) Packs-On and Packs-Off. In accordance with §§ 25.855 and 25.857, there must be a means to exclude hazardous quantities of smoke, flames, or extinguishing agent from any compartment occupied by crew or passengers. The FAA has historically found compliance to these requirements for packs-on operation but has not recognized the need to assess compliance with requirements for limited duration packs-off operation. A change in precedent set by historical practice is beyond the scope of this informational memorandum. The Transport Standards Staff (TSS) recognizes that service experience to date has not demonstrated that 68
packs-off operations have resulted in hazardous quantities of smoke. Therefore, at this time, determination that packs-off operation is acceptable can be predicated on an FAA finding that no unsafe condition due to limited duration packs-off operation would result should a cargo compartment fire occur. Criteria that should be considered include: (1) packs-on operation will not allow any smoke from the cargo compartment to penetrate the passenger compartment; and
(2) during limited duration packs-off operations the cargo compartment smoke detection system is effective and the aircondition packs can be turned on and returned to the approved packs-on configuration to exclude hazardous quantities of smoke. The local ACO may make a determination of compliance to the aforementioned criteria based upon available test data, analysis and extrapolation of these data, as has been historically accepted to demonstrate compliance to these and other sections of part 25.
(5) Fresh Air and Normal Operating Conditions. The following policy is extracted from an FAA memorandum dated September 10, 1997, in response to questions regarding the terms “fresh air” and “normal operating conditions” as it applies to compliance with § 25.831.
(a) The term “fresh air” was first documented with the ventilation requirements in § 4b.371 of the CAR. Section 4b.371(a) of the CAR required that all crew compartments be ventilated with a sufficient amount of fresh air. It was specified that “an outside air supply of approximately 10 cubic feet per minute is considered a minimum for each crewmember.” This requirement was later codified into 14 CFR § 25.831(a).
(b) Notice of Proposed Rulemaking (NPRM) 89-31 first proposed that § 25.831(a) be amended to include additional minimum airflow requirements for both crew and passengers.
NPRM 89-31 and Amendment 25-87 proposed that the minimum fresh airflow of 10 cubic feet per minute per crewmember be provided to each occupant during normal operation. Both the “Discussion” section of NPRM 89-31 and the “Background” section of Amendment 25-87 state that some airplanes “incorporate ventilation systems in which fresh air is augmented with conditioned and recirculated air.” It was specified that the rule change would permit a ventilation system that uses a mixture of the minimum amount of fresh air and any desired quantity of recirculated air that is shown to be uncontaminated by odors, particulates, or gases. It is stated that the “minimum amount of fresh air is specified by weight. . . .” Ten cubic feet of standard air at a typical cabin altitude of 8,000 feet weighs approximately 0.55 pounds, which is how the final rule was stated. This provides a clear distinction that the minimum amount of fresh air (outside air) is 0.55 pounds per minute per person, but may be augmented by additional conditioned and recirculated air.
(c) Requests have been made that “normal operating conditions” as used in § 25.831(a) be interpreted to mean normal cruise conditions with this interpretation excluding ground, climb, descent, and holding operations. The FAA does not agree. Ground, climb, descent, and holding operations are considered normal operating conditions. However, it should be noted that the wording in the preamble to the final rule stated that for normal operating conditions, the ventilation system must be designed to provide the fresh airflow. This was a change from the NPRM that which stated that each occupant must be provided the fresh airflow.
The preamble to Amendment 25-87 states that it is clear that the additional airflow is not 69