approved performance levels on each type design would be required. The actual content of the test program would depend on many factors, including the similarity of the old and new designs, the relative performance envelopes of the demonstrated brake and candidate airplane, effect of the new brake design on fuse plug performance (if applicable), presence or absence of antiskid systems, and possible effects of the change on ground handling. It is also possible that the addition of these new brakes to certain existing airplanes could be considered to be a minor change, in which case AC 25-7A (formerly Order 8110.8, paragraph 89(b)) would apply, and only uninstrumented functional landings would be required. It was recognized that it may be impossible to duplicate test data that may have been created over 20 years ago, especially if the airplane in question is not equipped with an antiskid system. In this case, it may be appropriate to apply a suitable performance penalty to allow for this uncertainty. In any event, engineering judgment should be applied to each individual situation so that the intent of the test program discussed above will be followed.
(d) While the performance of the new brake must be no less than that of the originally approved brake, it also should not be greater; e.g., a higher brake torque is desirable for reducing stopping distance but may be undesirable for structural integrity of other components of the landing gear. Original landing gear designs are based on structural analysis, which could be adversely affected by a brake system change.
(11) Certification Requirements for Brake Components - Performance. The following is extracted from an FAA letter dated October 26, 1987, which addresses "major" and "minor" changes to aircraft brake components and explains FAA policy on this subject.
(a) Measured accelerate-stop distance, landing distance, and functional flight tests may be required depending upon an evaluation of the individual characteristics of each brake system change and in order to establish aircraft landing and RTO certification performance levels for a replacement or modified brake. The type and magnitude of flight tests required will depend on whether or not a requested change to the brake involves a change in heat sink capacity or torque requirements of the original certificated brake. In addition, such tests will also depend on whether or not an increase in the FAA certificated performance level is desired by the applicant, and whether the proposed change to the brake would affect the landing gear static or dynamic loads.
(b) The flight test procedures applicable to brake certification, among others, are contained in AC 25-7A, Flight Test Guide for Transport Category Airplanes (formerly FAA Order 8110.8). The testing requirements in AC 25-7A (formerly Order 8110.8, paragraph 89(b)), relate to the addition of a highly modified brake design to an existing type certificated airplane.
A highly modified brake is defined in this section as one which contains new or modified parts which in turn will cause a significant variance in the kinetic energy absorption characteristics of the brake. The FAA concurs that a change to either the rotors or stators in a previously approved brake could meet this definition, and be considered a major change. In order to adequately demonstrate the performance of a major change to the brakes or brake control system, a maximum kinetic energy RTO, as described in AC 25-7A (formerly Order 8110.8), would normally be required, as well as six functional takeoffs and landings. In addition, fuse plug 53
substantiation tests (melt and no-melt) would be required (if applicable), unless it can be demonstrated that heat transfer from the brake stack to the wheel is identical to the original.
Also, antiskid-on and antiskid-off tests (if applicable), qualitative taxi tests, and wet runway tests (antiskid-on, if applicable) would be required. Order 8110.8 has been canceled. Relevant portions of Order 8110.8 and additional information have been included in AC 25-7A, chapter 4, section 4, paragraph 55.
(c) Minor brake changes that cannot affect airplane braking performance may require functional landings. This may be required to verify airplane-pilot-brake-antiskid combination compatibility. Normally, five non-instrumented functional landings are considered sufficient to verify this compatibility. A change to thicker friction material, heavier heat sink elements, or other structural improvements generally fall into this minor change category, and the effect of the weight change on landing gear performance and other airplane effects would be evaluated. If the change to the brake resulted in a lighter weight heat sink, the effects of this change would be carefully evaluated to ensure that the thermal characteristics of the brake, wheel, axle, fuse plugs, or other landing gear structure is not adversely affected.
(d) Technical Standard Order (TSO) approval of a modification to a brake is only the first step towards approval for the brake to be installed on an airplane. In each case, the modification must be shown to have no adverse effect on airplane performance. Depending on the magnitude of the proposed change, this demonstration may consist of functional tests only, a full test program, or a selection of the various test procedures described in AC 25-7A (formerly Order 8110.8). Enough flexibility exists in FAA procedures to allow for a thorough evaluation of a proposed brake change without causing undue burden on the applicant. In any event, if there is a question whether or not a given modification to a brake will result in a change to the certificated performance of the airplane, FAA policy has been to demonstrate the performance change on the airplane, or, at the very least, to impose a suitable performance penalty so as to cover any eventuality. There are no plans to relax this requirement.
(12) Approval of Brake Components Utilizing New Brake Friction Material. The following is extracted from an FAA memorandum dated July 27, 1987, which addresses guidance regarding certification of brake components utilizing new brake friction material.
(a) This is in response to questions regarding an approval for new replacement brake pads. For the purpose of approving a replacement brake pad, the FAA may issue a design approval by either a Parts Manufacturer Approval (PMA) or a Technical Standard Order Authorization (TSOA) followed by a Supplemental Type Certificate (STC) for installation, or a procedure using an STC followed by a PMA for production. Each of these approval methods is discussed below. Once a PMA approval is given, the applicant could then mark the brake assembly with his own nameplate, indicating the method of approval (STC number), without altering the existing TSO nameplate.
(b) Issuance of a PMA. If the applicant intends to show identicality with existing TSO-authorized parts, he must consider not only the form and fit of the parts, but also the chemical and/or metallurgical characteristics (including microstructure, surface and cross- 54
sectional hardness, and material spectrum analysis), and process and manufacturing specifications. Previous experience with various brake manufacturers has shown that it is extremely difficult to duplicate the physical and chemical characteristics of brake lining materials. For example, two linings with similar hardness or other measurable characteristics could have been produced using different process specifications. If the applicant satisfactorily shows that his parts are indeed identical to the originals, the change could then be considered to be a "minor change," as discussed in AC 25-7A (formerly Order 8110.8, paragraphs 89(b, (c)).
Five non-instrumented landings would be sufficient to demonstrate compatibility between the airplane, pilot, brake, and anti-skid systems on the airplane. With respect to the TSO, a statement of conformance and submittal of the data showing identicality would be sufficient.
Order 8110.8 has been canceled. Relevant portions of Order 8110.8 and additional information have been included in AC 25-7A, chapter 4, section 4, paragraph 55.
(c) Issuance of a TSOA+STC or an STC+PMA. If the applicant is unable to demonstrate identicality, the change must then be considered to be a major change, since the coefficient of friction and wear rates may be different, and the new parts could, therefore, cause a significant variance in the heat sink capacity, the torque characteristics, or the kinetic energy absorption characteristics of the brake. It would be necessary, therefore, for the applicant to demonstrate compliance with the pertinent parts of TSO-C26c, including the 100 landing stops and 1 accelerate-stop described in Table III of § 4.2 of the TSO.
(d) In addition to the TSO requirements, a maximum kinetic energy Rejected Takeoff (RTO), as described in AC 25-7A (formerly Order 8110.8), must be conducted in the airplane, as well as six functional takeoffs and landings. In addition, fuse plug substantiation tests (melt and no-melt) must be conducted, unless the applicant can demonstrate that heat transfer from the brake stack to the wheel is identical to the original. Also, antiskid-on and antiskid-off tests, qualitative taxi tests, and wet runway tests (antiskid-on) must be conducted.
These test procedures are described in AC 25-7A (formerly Order 8110.8, paragraph 89), and are required to adequately demonstrate the performance of the new lining material .
(e) If the applicant successfully demonstrates that the performance of the brake with his parts installed is identical to the original, he may mark the brake as described above. If the demonstrated performance is greater than that of the original, however, an FAA evaluation by the cognizant ACO is essential, since original landing gear designs are based on structural analysis which could be adversely affected by a brake system change.
(13) Maximum Quick Turnaround Times. The following is extracted from an FAA letter dated August 19, 1983, which addresses a request to intermix brakes from different manufacturers for testing of the fuse plug integrity and receive certification credit for each brake/wheel system.
(a) It is fundamental FAA policy to test the complete configuration of an airplane system that is to be certificated for transportation service. In this case the applicant proposed to certificate two unmixed configurations, the Original Equipment Manufacturer 1(OEM1) and the Original Equipment Manufacturer 2 (OEM2) wheel/brake systems. In general, the FAA does not 55
certificate unmixed configurations based solely on a test of mixed configurations. Further, certification of the mixed configuration requires extensive testing, beyond the test outlined in AC 25-7A (formerly FAA Order 8110.8). Order 8110.8 has been canceled. However, the relevant portions of the Order and additional information have been included in AC 25-7A, chapter 4, section 4, paragraph 55.
(b) Precedent tests previously accepted by the FAA have been cited. These cases were judged on their merits, as must be done here. Approval of the eutectic melt temperature reduction was based on dynamometer tests and an analysis. In that case, wherein the wheel/brake configuration was fixed and test date/analysis were provided, the FAA judged equivalency in a single system element (fuse plugs). The FAA did not consider it appropriate to compare the equivalency finding in the foregoing case to that of mixing wheel/brake configurations for establishing new turnaround limitations.
(c) The OEM1 and OEM2 wheel/brake configurations are “similar in design and performance" was cited as justification to allow mixed wheel/brake fuse plug turnaround testing.
The FAA noted that the wheel brake designs were intended to mount on the same axle using the same hydraulic and antiskid/autobrake systems and brake torque reaction rods. Both wheel/ brake assemblies have double heat shields and the tolerance of the OEM1 fuse plug is inside the tolerance of the OEM2 fuse plug. The nominal difference is not considered significant.
(d) The structural arrangement in detail, however, is different in a number of places, including in and around the fuse plugs. The FAA must assume the variations in metal mass and configuration will affect heat transfer. Also, there are differences in the hydraulic actuators. The brakes themselves are made up of proprietary materials that will exhibit different thermal reactions. The wheels are similar in appearance because they have to be interchangeable; however, it has not been established that they are similar relative to the fuse plug performance.
(e) "Significant margin exists for higher certificated no melt energy levels" is also proposed. It is the FAA's understanding that the applicant intends to use this margin, derived from dynamometer tests minus airplane test data available, to increase the fuse plug "no melt" energy. The FAA has determined this increase is a valid reason to substantiate by test both configurations, i.e., OEM1 and OEM2, with the wheels and brakes in the unmixed state.
(f) The applicant proposed that twice as many fuses be instrumented as in the basic certification. This would give useful empirical data, although the FAA does not require fuse plug instrumentation. In the final analysis, the success of the test is judged by whether the fuse plug integrity is maintained.
(g) In light of the foregoing, the FAA has determined that each wheel/brake configuration should be tested separately for the "no melt" condition to provide a technically defensible minimum wheel/brake fuse plug sample size. This decision is consistent with FAA policy published in AC 25-7A, Flight Test Guide for Transport Category Airplanes, chapter 4, section 4, paragraph 55. This information was in Order 8110.8, paragraphs 89(a), (b), and (c), 56
which has been canceled. However, the relevant portions of the Order and additional information have been included in AC 25-7A,
(h) It has been suggested that the proposed intermix and test procedure ensures minimal data scatter between brakes. If this statement means that the test data scatter between the two tire/wheel configurations will be minimized because all the data will be collected on one test run versus two, which may occur at separate times of the day or different days under varying conditions, then we can concur. However, this does not lend credence to the selection of an inadequate sample size. The proposal does not address what occurs if differences in brake performance are observed; or how to establish a significant difference (which could affect turnaround times), when comparing one brake system to another.
e. References. The addresses for ordering the latest revision of advisory circulars, technical standard orders, and other referenced documents listed below can be found in the Appendix 4 to this AC.
TSO-C26, was an acceptable standard to CAA but not part of the regulations.
TSO-C26a, was part of regulations as § 514.72 of the CAR.
TSO-C26b, was part of regulations as § 37.172.
TSO-C26c, was part of regulations as § 37.172 of 14 CFR.
TSO-C26c with Addendum I, was removed from regulations (§ 37.172, Amendment 25-52, 1980) and became a voluntary standard.
AC 25-7A, Flight Test Guide for Transport Category Airplanes (formerly FAA Order 8110.8).
AC 43.13-1A, Acceptable Methods, Techniques and Practices- Aircraft Inspection and Repair; L. G. Equipment.
FAA Letter, Dynamometer Test Guidelines to Establish Brake wear Limits.
FAA's Wheels and Brakes Approval Process Videos, parts 1 and 2.
SAE AS-1145A - Aircraft Brake Temperature Monitor System.
SAE ARP-1907 - Automatic Braking Systems Requirements.
SAE AIR-1064C - Brake Dynamics.
SAE ARP-1070B - Design and Testing of Antiskid Brake Control.
SAE AIR-1739 - Information on Antiskid Systems.
SAE ARP-813B - Maintainability Recommendations for Aircraft Wheels and Brakes.
SAE ARP-1619 - Replacement and Modified Brakes and Wheels.
SAE AS-483A - Skid Control Equipment.
SAE ARP-862A - Skid Control Performance.
SAE AIR-1934A - Use of Carbon Heat Sink Brakes on Aircraft.
SAE ARP-597C - Wheels and Brakes, Supplementary Criteria for Design Endurance.
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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