Chapter 3. EQUIPMENT
Section 1. GENERAL
47. SECTION 25.1301 - FUNCTION AND INSTALLATION.
a. Rule Text.
Each item of installed equipment must-
(a) Be of a kind and design appropriate to its intended function;
(b) Be labeled as to its identification, function, or operating limitations, or any applicable combination of these factors;
(c) Be installed according to limitations specified for that equipment; and
(d) Function properly when installed.
b. Intent of Rule. The intent of this requirement is to define general conditions for certification of all installed equipment regardless if it's covered under another requirement. This requirement applies to all equipment/systems whether required as minimum equipment for installation on airplanes or non-required/non-essential equipment (e.g., advisory systems, pilot aids, or passenger comfort related amenities).
c. Background. This requirement originated under § 4b.682 of the Civil Air Regulations (CAR), October 1, 1949, with reference to items of equipment for which type certification was required outlined in part 15 of the CAR. Effective July 20, 1950, it was recodified as § 4b.601 by deleting reference to part 15 per Amendment 04b-2 (effective February 6, 1950), and allowing approval of materials, parts, and appliances per § 04b.05 and the new TSO system.
Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the CAR. Section 4b.601 of the CAR became § 25.1301 of 14 CFR.
(1) Harmonization. This regulation is the subject of a Federal Aviation Regulations/Joint Aviation Requirements (FAR/JAR) harmonization effort under Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group is recommending revisions to §§ 25.1301, 25.1309, a new 25.1310, and a revised Advisory Circular AC 25.1309- 1B. Section 25.1301(d) will be deleted as being redundant with the proposed § 25.1309(a).
d. Policy/Compliance Methods. Information regarding installation limitations and proper functioning is normally available from the equipment manufacturers in their installation and operations manuals. For example, TSO Rating Limits apply under § 25.1309(c). Under § 25.1301(d), TSO is not an installation approval. The user/installer is responsible for form, fit, and function.
(1) Joint Aviation Requirements (JAR) ACJ 25.1301(b). The following guidance is extracted from JAR ACJ 25.1301(b):
(a) An adequate means of identification should be provided for all cables, connectors, and terminals. The means employed should be such as to ensure that the identification does not deteriorate under service conditions.
(b) When pipelines (hydraulic/pneumatic, etc.) are marked for the purpose of distinguishing their functions, the markings should be such that the risk of confusion by maintenance or servicing personnel will be minimized. Distinction by means of color markings alone is not acceptable. The use of alphabetic or numerical symbols will be acceptable if recognition depends upon reference to a master key and any relation between symbol and function is carefully avoided. Specification ISO.12 gives acceptable graphical markings.
e. Reference. None.
48. SECTION 25.1309 - EQUIPMENT, SYSTEMS, AND INSTALLATION.
a. Rule Text.
(a) The equipment, systems, and installations whose functioning is required by this subchapter, must be designed to ensure that they perform their intended functions under any foreseeable operating condition.
(b) The airplane systems and associated components, considered separately and in relation to other systems, must be designed so that-
(1) The occurrence of any failure condition which would prevent the continued safe flight and landing of the airplane is extremely improbable, and
(2) The occurrence of any other failure conditions which would reduce the capability of the airplane or the ability of the crew to cope with adverse operating conditions is improbable.
(c) Warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action.
Systems, controls, and associated monitoring and warning means must be designed to minimize crew errors which could create additional hazards.
(d) Compliance with the requirements of paragraph (b) of this section must be shown by analysis, and where necessary, by appropriate ground, flight, or simulator tests. The analysis must consider-
(1) Possible modes of failure, including malfunctions and damage from external sources.
(2) The probability of multiple failures and undetected failures.
(3) The resulting effects on the airplane and occupants, considering the stage of flight and operating conditions, and
(4) The crew warning cues, corrective action required, and the capability of detecting faults.
(e) Each installation whose functioning is required by this subchapter, and that requires a power supply, is an ''essential load'' on the power supply. The power sources and the system must be able to supply the following power loads in probable operating combinations and for probable durations:
(1) Loads connected to the system with the system functioning normally.
(2) Essential loads, after failure of any one prime mover, power converter, or energy storage device.
(3) Essential loads after failure of-
(i) Any one engine on two-engine airplanes; and
(ii) Any two engines on three-or-more-engine airplanes.
(4) Essential loads for which an alternate source of power is required by this chapter, after any failure or malfunction in any one power supply system, distribution system, or other utilization system.
(f) In determining compliance with paragraphs (e) (2) and (3) of this section, the power loads may be assumed to be reduced under a monitoring procedure consistent with safety in the kinds of operation authorized. Loads not required in controlled flight need not be considered for the two-engine-inoperative condition on airplanes with three or more engines.
(g) In showing compliance with paragraphs (a) and (b) of this section with regard to the electrical system and equipment design and installation, critical environmental conditions must be considered. For electrical generation, distribution, and utilization equipment required by or used in complying with this chapter, except equipment covered by Technical Standard Orders containing environmental test procedures, the ability to provide continuous, safe service under foreseeable environmental conditions may be shown by environmental tests, design analysis, or reference to previous comparable service experience on other aircraft.
[Amdt. 25-23, 35 FR 5679, Apr. 8, 1970, as amended by Amdt. 25-38, 41 FR 55467, Dec. 20, 1976; Amdt. 25-41, 42 FR 36970, Jul. 18, 1977]
b. Intent of Rule. This regulation covers, but is not limited to, mechanical, electrical, pneumatic, and hydraulic power sources, associated distribution, and corresponding utilization systems.
c. Background. This regulation originated under Amendment 4b-6 of the Civil Air Regulations (CAR), effective March 5, 1952, as § 4b.606 and was codified on December 31, 1953. It was amended under Amendment 4b-1, effective May 18, 1954, by clarifying the allowed assumptions in the determination of probable operating combinations of essential loads for the power failure conditions. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the CAR. Section 4b.606 of the CAR became § 25.1309 of 14 CFR.
(1) Amendment 25-23 (April 8, 1970) added these requirements:
(i) Where the consequences of complete loss of system function would be catastrophic, combinations of failures and multiple failures due to common causes must be considered, and sufficient reliability, redundancy and isolation provided to make catastrophic systems failure extremely improbable.
(ii) Occurrence of failures that result in serious degradation of flight characteristics, a large increase in crew work-load, or difficult emergency procedures be improbable.
(iii) Warning information must be provided to alert the crew to unsafe system operating conditions and to enable them to take corrective action.
(iv) Compliance to (i), (ii), and (iii) be shown by analysis and ground/flight/simulator tests.
(2) Amendment 25-38 (February 1, 1977) amended the title by inserting a comma between the words "equipment" and "Systems" and between the words "Systems" and "and."
The change was strictly editorial.
(3) Amendment 25-41 (September 1, 1977(revised §§ 25.1309(b)(2), (c), lead-in of (d),
(e)(3), and (f). The reference to occupant injury in (b)(2) was deleted because the matter of preventing injuries to occupants is covered elsewhere in the regulations; deleted reference to (c) in (d) because it could have been unreasonably burdensome for compliance; added provisions in
(c) to minimize crew errors; revised (e)(3) and (f) related to electrical systems.
(4) Harmonization. This regulation is the subject of a Federal Aviation Regulations/Joint Aviation Requirements (FAR/JAR) harmonization effort under Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group is recommending revisions to §§ 25.1301, 25.1309, a new 25.1310, and a revised AC 25.1309-1B. Section
25.1301(d) will be deleted as being redundant with the proposed § 25.1309(a).
d. Policy/Compliance Methods. The term "subchapter" in § 25.1309(a) is intended to cover not only subchapter "C," but also the equipment, systems, and installations not specifically required by subchapter "C" but installed in airplanes in order to engage in operations covered by other subchapters. Dependence for safety of flight might be placed on installations not otherwise mentioned in the rules.
(1) Probability of a Fire. The following is extracted from an FAA memorandum, dated March 9, 1995. This is in response to a request for guidance regarding the use of the probability of a fire in a failure analysis when showing compliance with § 25.1309. The focus of the request was directed at the three issues addressed below:
(a) The first issue concerns whether the occurrence of a cargo compartment fire should be considered to have a probability of one, or something less than one. Advisory Circular (AC) 25.1309-1A, paragraph 8e, "Operational and Environmental Conditions," allows that random conditions may be considered to have a probability of occurrence less than one, and may usually be included in a safety analysis. The AC indicates that a random condition is a condition 128
for which the airplane is not designed, and in which the airplane is not normally approved to operate. It also indicates that a random condition may be used in the analysis even when the system under analysis is designed to protect against the occurrence of the random condition. The AC provides, as an example, that it would be reasonable and rational to use a probability of less than one of encountering hazardous turbulence or gust levels after the failure of a structural load alleviation system. A probability less than one of fire occurring after a failure of the fire protection system is similar to this example, and may be used in the analysis. Advisory Circular
25.1309-1A also provides counter-examples for conditions which should not be considered random, and for which a probability of one should be used. These are conditions for which the airplane is designed. The examples provided, instrument meteorological conditions and Category III weather operations, are conditions in which the airplane would be expected to operate as a matter of course, and for which operational approval would be granted.
(b) The second issue concerns what value less than one should be assigned to the probability of the occurrence of a fire. Advisory Circular 25.1309-1A, paragraph 8e, provides guidance that the statistically-derived probability used in the analysis should be based on an applicable supporting database and a valid statistical distribution. When requesting approval for the use of the probability of a random condition in a safety analysis, it is incumbent on the applicant to supply the data, show the applicability of the database from which the data is supplied, and derive a valid statistical conclusion. The ACO should then evaluate the applicant's statistical information and determine if the value used in the analysis is supported by the data presented. This value must be reassessed for subsequent programs, as service experience gained in the future may require the probability of the occurrence to be re-evaluated.
(c) The third issue is whether the required safety level reached through the use of the Maintenance Steering Group, Revision 3 (MSG-3) procedures is higher than that reached using a § 25.1309 related analysis. We contend that this is not so, and that a like-comparison of the two sets of procedures is not valid. The § 25.1309 analysis process is directed at assessing the contributions of failures to given failure conditions, and to directing the airplane or system design appropriately. The MSG-3 process is directed at determining appropriate maintenance actions given the contribution of a failure to a reduction in safety. Findings from the § 25.1309 analysis process are used as starting points for certain MSG-3 processes to determine maintenance activities and intervals, or whether the maintenance process can adequately minimize the risk elements assigned to it. The MSG-3 procedures must assume the combination of a system failure with the occurrence of the condition, which the system was designed to protect against, in order to account for hidden failures when determining maintenance actions.
Expected or allowable probabilities related to system failures are not derived through the MSG-3 process. In applying the above guidance, note that § 25.1309 is a rule of general applicability, and should not be used to replace a more specific and stringent requirement. Cargo compartments, and compartment fire detection and protection systems must meet requirements specified in §§ 25.855, 25.857, and 25.858, regardless of probabilities as determined in a § 25.1309 related analysis.
(2) Examples. For an example of compliance with § 25.1309(c), see paragraph d(1) under § 25.1441, Oxygen equipment and supply, of this AC. Another example of compliance is included under paragraph d(2), § 25.855, Cargo or baggage compartments, of this AC.
(3) Safe and Reliable. The following is extracted from an FAA memorandum dated October 26, 1990, and addresses an inquiry regarding (i) The meaning of "safe and reliable" used in §§ 25.109(b) and 25.125(b)(3) in terms of AC 25.1309-1A probability, and (ii) The acceptable failure probability for deceleration devices like anti-skid and ground spoilers that have relatively large and small effects on landing distance. The FAA response follows:
(a) Safe and reliable is generally used to mean that a failure condition is improbable. In terms of AC 25.1309-1A quantitative probability terms, improbable failure conditions are those having a probability on the order of 1 X 10-5 or less.
(b) Each deceleration device, such as anti-skid and ground spoilers, would be expected to have a failure condition that is at least improbable (i.e. 1 X 10-5 or less) regardless of its effect on stopping distance.
e. References. For policy and guidance on compliance with this requirement, see AC 25.1309-1A, System Design Analysis, issued June 21, 1988, or latest revision, and AC 25-19, Certification Maintenance Requirements, issued November 28, 1994, or latest revision.
49 - 51. [RESERVED]
Section 2. INSTRUMENTS: INSTALLATION
52. SECTION 25.1325 - STATIC PRESSURE SYSTEMS.
a. Rule Text.
(a) Each instrument with static air case connections must be vented to the outside atmosphere through an appropriate piping system.
(b) Each static port must be designed and located in such manner that the static pressure system performance is least affected by airflow variation, or by moisture or other foreign matter, and that the correlation between air pressure in the static pressure system and true ambient atmospheric static pressure is not changed when the airplane is exposed to the continuous and intermittent maximum icing conditions defined in Appendix C of this Part.
(c) The design and installation of the static pressure system must be such that-
(1) Positive drainage of moisture is provided; chafing of the tubing and excessive distortion or restriction at bends in the tubing is avoided; and the materials used are durable, suitable for the purpose intended, and protected against corrosion;
and
(2) It is airtight except for the port into the atmosphere. A proof test must be conducted to demonstrate the integrity of the static pressure system in the following manner:
(i) Unpressurized airplanes. Evacuate the static pressure system to a pressure differential of approximately 1 inch of mercury or to a reading on the altimeter, 1,000 feet above the airplane elevation at the time of the test. Without additional pumping for a period of 1 minute, the loss of indicated altitude must not exceed 100 feet on the altimeter.
(ii) Pressurized airplanes. Evacuate the static pressure system until a pressure differential equivalent to the maximum cabin pressure differential for which the airplane is type certificated is achieved. Without additional pumping for a period of 1 minute, the loss of indicated altitude must not exceed 2 percent of the equivalent altitude of the maximum cabin differential pressure or 100 feet, whichever is greater.
(d) Each pressure altimeter must be approved and must be calibrated to indicate pressure altitude in a standard atmosphere, with a minimum practicable calibration error when the corresponding static pressures are applied.
(e) Each system must be designed and installed so that the error in indicated pressure altitude, at sea level, with a standard atmosphere, excluding instrument calibration error, does not result in an error of more than +/- 30 feet per 100 knots speed for the appropriate configuration in the speed range between 1.3 Vso with flaps extended and 1.8 Vs1 with flaps retracted. However, the error need not be less than +/- 30 feet.
(f) If an altimeter system is fitted with a device that provides corrections to the altimeter indication, the device must be designed and installed in such manner that it can be bypassed when it malfunctions, unless an alternate altimeter system is provided. Each correction device must be fitted with a means for indicating the occurrence of reasonably probable malfunctions, including power failure, to the flight crew. The indicating means must be effective for any cockpit lighting condition likely to occur.
(g) Except as provided in paragraph (h) of this section, if the static pressure system incorporates both a primary and an alternate static pressure source, the means for selecting one or the other source must be designed so that-
(1) When either source is selected, the other is blocked off; and
(2) Both sources cannot be blocked off simultaneously.
(h) For unpressurized airplanes, paragraph (g)(1) of this section does not apply if it can be demonstrated that the static pressure system calibration, when either static pressure source is selected, is not changed by the other static pressure source being open or blocked.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-5, 30 FR 8261, Jun. 29, 1965; Amdt. 25-12, 32 FR 7587, May 24, 1967; Amdt. 25- 41, 42 FR 36970, Jul. 18, 1977]
b. Intent of Rule. This rule provides minimum design and certification requirements for static pressure systems to ensure proper static system operation in varying operating conditions.
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). Many of the requirements in § 4b.612(b) of the CAR were carried over essentially unchanged to § 25.1325 of 14 CFR.
(1) Amendment 25-5 (June 29, 1965) added requirements for (1) operation in icing conditions and (2) devices that provide corrections to the altimeter indication.
(2) Amendment 25-12 (May 24, 1967) added requirements for static system proof testing for pressurized and unpressurized airplanes.
(3) Amendment 25-41 (July 18, 1977) added standards for static pressure systems, which incorporate the ability to select one or the other of primary and alternate static systems.
d. Policy/Compliance Methods. For policy and guidance on compliance with this requirement, refer to Advisory Circular (AC) 25-XX, Electrical Systems Handbook.
e. References. None.
Section 3. SAFETY EQUIPMENT
53. SECTION 25.1419 ICE PROTECTION.
a. Rule Text.
If certification with ice protection provisions is desired, the airplane must be able to safely operate in the continuous maximum and intermittent maximum icing conditions of appendix C. To establish that the airplane can operate within the continuous maximum and intermittent maximum conditions of appendix C:
(a) An analysis must be performed to establish that the ice protection for the various components of the airplane is adequate, taking into account the various airplane operational configurations; and
(b) To verify the ice protection analysis, to check for icing anomalies, and to demonstrate that the ice protection system and components are effective, the airplane or its components must be flight tested in the various operational configurations, in measured natural atmospheric icing conditions and, as found necessary, by one or more of the following means:
(1) Laboratory dry air or simulated icing tests, or a combination of both, of the components or models of the components.
(2) Flight dry air tests of the ice protection system as a whole, or of its individual components.
(3) Flight tests of the airplane or its components in measured simulated icing conditions.
(c) Caution information, such as an amber caution light or equivalent, must be provided to alert the flightcrew when the anti-ice or de-ice system is not functioning normally.
(d) For turbine engine powered airplanes, the ice protection provisions of this section are considered to be applicable primarily to the airframe. For the powerplant installation, certain additional provisions of Subpart E of this Part may be found applicable.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35 FR 5680, Apr. 8, 1970; Amdt. 25-72, 55 FR 29785, Jul. 20, 1990]
b. Intent of Rule. This rule provides standards for certification of an airplane with ice protection provisions. Certification for flight in icing conditions is optional at the discretion of the applicant. If the airplane is not certificated for flight in icing condition, appropriate limitations shall be placed in the type certificate data sheet and the airplane flight manual.
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). Many of the provisions in section 4b.640 of the CAR were carried over with minor word changes to § 25.1419 of 14 CFR. However, the intent of the CAR 4b.640 was unchanged.
Amendment 25-23 revised paragraph (c) to require flight tests in measured natural atmospheric icing conditions. Prior to Amendment 25-23 flight tests in measured natural atmospheric icing conditions were optional.
(1) Amendment 25-23 (April 8, 1970) added the requirements for flight testing in natural icing conditions contained in § 25.1419(c).
(2) Amendment 25-72 (July 20, 1990) rearranged the sub-paragraphs and inserted a new paragraph (c), which requires caution information when the anti-ice or de-ice system is not functioning normally. Prior to this amendment, a means to determine that a pneumatic de-icing boot system was working normally was required by § 25.1416. Section 25.1416 was removed to allow for the concept of the "dark cockpit.” (The term “dark cockpit” is descriptive language that refers to the absence of annunciation lights in the cockpit unless a system is operating abnormally.)
d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and AC 20-73 and AC 25.1419-1.
e. References. The addresses for ordering the latest revision of advisory circulars, and other referenced documents listed below can be found in the Appendix to this AC.
AC 20-73, Aircraft Ice Protection.
AC 23.1419-2, Certification of Part 23 Airplanes for Flight in Icing Conditions.
AC 25.1419-1, Certification of Transport Category Airplanes for Flight in Icing Conditions.
Report No. DOT/FAA/CT-88/8-1 - Aircraft Icing Handbook (three volumes) FAA Technical Report ADS-4 - Engineering summary of Airframe Icing Technical Data, December 1963. (Although most of the information contained in this report is still valid, some is outdated, and more usable information is now available through recent research and experience and is included in the Aircraft Icing Handbook.)
54 - 58. [RESERVED]
Section 4. MISCELLANEOUS EQUIPMENT
59. SECTION 25.1433 - VACUUM SYSTEMS.
a. Rule Text.
There must be means, in addition to the normal pressure relief, to automatically relieve the pressure in the discharge lines from the vacuum air pump when the delivery temperature of the air becomes unsafe.
[Amdt. 25-72, 55 FR 29785, Jul. 20, 1990]
b. Intent of Rule. This rule provides minimum design and certification requirements for vacuum systems, specifically to require automatic pressure relief in the presence of high delivery air temperatures.
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 requirements in section 4b.658 of the CAR were carried over essentially unchanged to § 25.1433 of 14 CFR.
(1) Amendment 25-72 (July 20, 1990) moved §§ 25.1433(b) and 25.1443(c), which dealt with fire protection for vacuum air systems, to § 25.869, Fire protection: Systems.
d. Policy/Compliance Methods. There is no existing written policy or guidance related to this subject in our files.
e. References. None.
60. SECTION 25.1435 - HYDRAULIC SYSTEMS.
a. Rule Text.
(a) Design.
(1) Each element of the hydraulic system must be designed to withstand, without deformation that would prevent it from performing its intended function, the design operating pressure loads in combination with limit structural loads which may be imposed.
(2) Each element of the hydraulic system must be able to withstand, without rupture, the design operating pressure loads multiplied by a factor of 1.5 in combination with ultimate structural loads that can reasonably occur simultaneously. Design operating pressure is maximum normal operating pressure, excluding transient pressure.
(b) Tests and analysis.
(1) A complete hydraulic system must be static tested to show that it can withstand
1.5 times the design operating pressure without a deformation of any part of the system that would prevent it from performing its intended function. Clearance between structural members and hydraulic system elements must be adequate and there must be no permanent detrimental deformation. For the purpose of this test, the pressure relief valve may be made inoperable to permit application of the required pressure.
(2) Compliance with 25.1309 for hydraulic systems must be shown by functional tests, endurance tests, and analyses. The entire system, or appropriate subsystems, must be tested in an airplane or in a mockup installation to determine proper performance and proper relation to other aircraft systems. The functional tests must include simulation of hydraulic system failure conditions. Endurance tests must simulate the repeated complete flights that could be expected to occur in service. Elements which fail during the tests must be modified in order to have the design deficiency corrected and, where necessary, must be sufficiently retested. Simulation of operating and environmental conditions must be completed on elements and appropriate portions of the hydraulic system to the extent necessary to evaluate the environmental effects. Compliance with 25.1309 must take into account the following:
(i) Static and dynamic loads including flight, ground, pilot, hydrostatic, inertial and thermally induced loads, and combinations thereof.
(ii) Motion, vibration, pressure transients, and fatigue.
(iii) Abrasion, corrosion, and erosion.
(iv) Fluid and material compatibility.
(v) Leakage and wear.
(c) Fire protection. Each hydraulic system using flammable hydraulic fluid must meet the applicable requirements of 25.863, 25.1183, 25.1185, and 25.1189.
[Amdt. 25-13, 32 FR 9154, Jun. 28, 1967, as amended by Amdt. 25-41, 42 FR 36971, Jul. 18, 1977; Amdt. 25-72, 55 FR 29786, Jul. 20, 1990]
b. Intent of Rule. The intent of this rule is to provide minimum design, performance, and safety requirements for transport category airplane hydraulic systems addressing the following aspects of component design and qualification, subsystem/system design, and system integration:
(1) Design operating loads in combination with limit and ultimate structural loads.
(2) Pressure transients and cyclic pressures.
(3) Environmental conditions.
(4) Fatigue and endurance life.
(5) Single and multiple failure modes.