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Section 2. FUEL SYSTEM COMPONENTS
43. SECTION 25.1001 - FUEL JETTISONING SYSTEM.
a. Rule Text.
(a) A fuel jettisoning system must be installed on each airplane unless it is shown that the airplane meets the climb requirements of §§ 25.119 and 25.121(d) at maximum takeoff weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprised of a takeoff, go-around, and landing at the airport of departure with the airplane configuration, speed, power, and thrust the same as that used in meeting the applicable takeoff, approach, and landing climb performance requirements of this part.
(b) If a fuel jettisoning system is required it must be capable of jettisoning enough fuel within 15 minutes, starting with the weight given in paragraph (a) of this section, to enable the airplane to meet the climb requirements of §§ 25.119 and
25.121(d), assuming that the fuel is jettisoned under the conditions, except weight, found least favorable during the flight tests prescribed in paragraph (c) of this section.
(c) Fuel jettisoning must be demonstrated beginning at maximum takeoff weight with flaps and landing gear up and in-
(1) A power-off glide at 1.4 Vs1;
(2) A climb at the one-engine inoperative best rate-of-climb speed, with the critical engine inoperative and the remaining engines at maximum continuous power; and
(3) Level flight at 1.4 Vs1 ; if the results of the tests in the conditions specified in paragraphs (c) (1) and (2) of this section show that this condition could be critical.
(d) During the flight tests prescribed in paragraph (c) of this section, it must be shown that-
(1) The fuel jettisoning system and its operation are free from fire hazard;
(2) The fuel discharges clear of any part of the airplane;
(3) Fuel or fumes do not enter any parts of the airplane; and
(4) The jettisoning operation does not adversely affect the controllability of the airplane.
(e) For reciprocating engine powered airplanes, means must be provided to prevent jettisoning the fuel in the tanks used for takeoff and landing below the level allowing 45 minutes flight at 75 percent maximum continuous power.
However, if there is an auxiliary control independent of the main jettisoning control, the system may be designed to jettison the remaining fuel by means of the auxiliary jettisoning control.
(f) For turbine engine powered airplanes, means must be provided to prevent jettisoning the fuel in the tanks used for takeoff and landing below the level 119
allowing climb from sea level to 10,000 feet and thereafter allowing 45 minutes cruise at a speed for maximum range. However, if there is an auxiliary control independent of the main jettisoning control, the system may be designed to jettison the remaining fuel by means of the auxiliary jettisoning control.
(g) The fuel jettisoning valve must be designed to allow flight personnel to close the valve during any part of the jettisoning operation.
(h) Unless it is shown that using any means (including flaps, slots, and slats) for changing the airflow across or around the wings does not adversely affect fuel jettisoning, there must be a placard, adjacent to the jettisoning control, to warn flight crewmembers against jettisoning fuel while the means that change the airflow are being used.
(i) The fuel jettisoning system must be designed so that any reasonably probable single malfunction in the system will not result in a hazardous condition due to unsymmetrical jettisoning of, or inability to jettison, fuel.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-18, 33 FR 12226, Aug. 30, 1968; Amdt. 25-57, 49 FR 6848, Feb. 23, 1984]
NOTE: This regulation 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 working group may recommend revisions to the regulation and any associated advisory material.
NOTE: For policy and guidance on compliance with this requirement, see Advisory Circular (AC) 25-XX, Propulsion Systems Handbook. This regulation may require special consideration for certain equipment where the airplane is not capable of a return landing without exceeding equipment ratings/capabilities such as brakes and tires. Brake maximum kinetic energy rating(s) and tire maximum speed ratings may be exceeded for an immediate return/turnback, or a flapless landing, especially for large two engine airplanes.
Section 3. POWERPLANT FIRE PROTECTION
44. SECTION 25.1183 - FLAMMABLE FLUID-CARRYING COMPONENTS.
a. Rule Text.
(a) Except as provided in paragraph (b) of this section, each line, fitting, and other component carrying flammable fluid in any area subject to engine fire conditions, and each component which conveys or contains flammable fluid in a designated fire zone must be fire resistant, except that flammable fluid tanks and supports in a designated fire zone must be fireproof or be enclosed by a fireproof shield unless damage by fire to any non-fireproof part will not cause leakage or spillage of flammable fluid. Components must be shielded or located to safeguard against the ignition of leaking flammable fluid. An integral oil sump of less than 25-quart capacity on a reciprocating engine need not be fireproof nor be enclosed by a fireproof shield.
(b) Paragraph (a) of this section does not apply to-
(1) Lines, fittings, and components which are already approved as part of a type certificated engine; and
(2) Vent and drain lines, and their fittings, whose failure will not result in, or add to, a fire hazard.
(Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-11, 32 FR 6913, May 5, 1967; Amdt. 25-36, 39 FR 35461, Oct. 1, 1974; Amdt. 25-57, 49 FR 6849, Feb. 23, 1984)
NOTE: For policy and guidance on compliance with this requirement, see Advisory Circular (AC) 25-XX, Propulsion Systems Handbook, chapter 4, section 9. Section 25.1435(c) - Hydraulic systems - Fire protection, requires compliance with § 25.1183.
NOTE: Under planned harmonization effort, paragraph 25.1183(c) of the JAR will be adopted by FAA as § 25.1183(c); the text is as follows:
"(c) All components, including ducts, within a designated fire zone must be fireproof if, when exposed to or damaged by fire, they could -
(1) Result in fire spreading to other regions of the airplane, or
(2) Cause unintentional operation of, or inability to operate, essential services or equipment."
45. SECTION 25.1185 - FLAMMABLE FLUIDS.
a. Rule Text.
(a) Except for the integral oil sumps specified in 25.1013 (a), no tank or reservoir that is a part of a system containing flammable fluids or gases may be in a designated fire zone unless the fluid contained, the design of the system, the materials used in the tank, the shut-off means, and all connections, lines, and control provide a degree of safety equal to that which would exist if the tank or reservoir were outside such a zone.
(b) There must be at least one-half inch of clear airspace between each tank or reservoir and each firewall or shroud isolating a designated fire zone.
(c) Absorbent materials close to flammable fluid system components that might leak must be covered or treated to prevent the absorption of hazardous quantities of fluids.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964 as amended by Amdt. 25-19, 33 FR15410, Oct. 17, 1968]
NOTE: For policy and guidance on compliance with this requirement, see Advisory Circular (AC) 25-XX, Propulsion Systems Handbook, chapter 4, section 9. Section 25.1435(c) - Hydraulic systems - Fire protection, requires compliance with § 25.1185.
46. SECTION 25.1189 - SHUTOFF MEANS.
a. Rule Text.
(a) Each engine installation and each fire zone specified in § 25.1181(a) (4) and
(5) must have a means to shut off or otherwise prevent hazardous quantities of fuel, oil, deicer, and other flammable fluids, from flowing into, within, or through any designated fire zone, except that shutoff means are not required for-
(1) Lines, fittings, and components forming an integral part of an engine; and
(2) Oil systems for turbine engine installations in which all components of the system in a designated fire zone, including oil tanks, are fireproof or located in areas not subject to engine fire conditions.
(b) The closing of any fuel shutoff valve for any engine may not make fuel unavailable to the remaining engines.
(c) Operation of any shutoff may not interfere with the later emergency operation of other equipment, such as the means for feathering the propeller.
(d) Each flammable fluid shutoff means and control must be fireproof or must be located and protected so that any fire in a fire zone will not affect its operation.
(e) No hazardous quantity of flammable fluid may drain into any designated fire zone after shutoff.
(f) There must be means to guard against inadvertent operation of the shutoff means and to make it possible for the crew to reopen the shutoff means in flight after it has been closed.
(g) Each tank-to-engine shutoff valve must be located so that the operation of the valve will not be affected by powerplant or engine mount structural failure.
(h) Each shutoff valve must have a means to relieve excessive pressure accumulation unless a means for pressure relief is otherwise provided in the system.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35FR 5677, Apr. 8, 1970; Amdt. 25-57, 49 FR 6849, Feb. 23, 1984]
NOTE: This regulation is the subject of a Federal Aviation Regulations/Joint Aivation Requirements (FAR/JAR) harmonization effort under the Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group is planning to recommend criteria for compliance as advisory material.
NOTE: For policy and guidance on compliance with this requirement, see Advisory Circular (AC) 25-XX, Propulsion Systems Handbook, chapter 4, section 9. Section 25.1435(c) - Hydraulic systems - Fire protection, requires compliance with § 25.1189.
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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.