SECTION 27. FUEL SYSTEM COMPONENTS
483. § 29.991 FUEL PUMPS.
a. Explanation.
(1) Section 29.991, Paragraph (a) provides a definition of the main pump(s) and § 29.991, Paragraph (b) requires an "emergency pump(s)." The main pump(s) that is certified as part of the engine does not fall under § 29.991 requirements. The main pump(s) discussed under § 29.991 should therefore be considered "main aircraft pump(s)."
(2) The main aircraft pump(s) consists of whatever pump(s) is required to meet engine or fuel system operation throughout the range of ambient temperature, fuel temperature, fuel pressure, altitude, and fuel types intended for the rotorcraft. If the main aircraft pump(s) is required to meet the above criteria, then an emergency pump(s) is required.
b. Procedures.
(1) Each pump classified as a main aircraft pump, which is also a positive displacement pump, must have provisions for a fuel bypass. An exception is made for fuel injection pumps used on certain reciprocating engines and for the positive displacement, high pressure, fuel pumps routinely used in turbine engines. The bypass may be accomplished via internal spring check valve and fuel passage, or by external plumbing and a check valve. High capacity positive displacement pumps with internal pressure relief and recirculation passages should be checked for overheating if they may be expected to operate continuously at or near 100 percent recirculation.
(2) Section 29.991, Paragraph (b) specifies a requirement for "emergency" pumps to provide the necessary fuel after failure of any (one) main aircraft pump.
(Injection pumps and high pressure pumps used on turbine engines are exempt.) As stated in this rule, the "emergency" pump must be operated continuously or started automatically to assure continued normal operation of the engine. For some multiengine rotorcraft, another main aircraft pump may possibly be used as the required "emergency" pump. In this case, the dual role of this pump requires it to have capacity to feed two engines at the critical pressure/flow condition. Availability of fuel flow from this backup pump must be automatic and this function should be verified in the preflight check procedure. For Category A rotorcraft, a comprehensive fault analysis of the fuel system is mandatory to assure compliance with § 29.903, Paragraph (b).
(3) Section 29.991, Paragraphs (c)(1)(i) and (il) address the situation, usually associated with supercharged reciprocating engines, where fuel pressure must be modulated with respect to carburetor deck pressure. This is accomplished with Par 483 775
interconnecting air lines from the carburetor intake (after the supercharger) to the pressure relief connection on the fuel pumps). A similar connection from the carburetor intake to the vented side of the fuel pressure gauge is needed to obtain correct fuel pressure reading. These systems may require orifices and/or surge chambers to operate correctly.
(4) Section 29.991, Paragraphs (c)(2) and (3) requires seal drains which drain safely. A drain impingement test is normally required to verify safe drainage. Use of a colored dye to simulate fuel discharge at the drain line exit or a fluid sensitive coating (Bon Ami) on the aircraft skins will facilitate evaluation of the safety aspects of drain impingement. Pump seal drain requirements would not be applicable for tank immersed pumps.
483A. § 29.991 (Amendment 29-26) FUEL PUMPS.
a. Explanation. Amendment 29-26 revises § 29.991 to clarify fuel pump redundancy requirements. Redundancy for fuel pump failure includes consideration of both the pump and the pump motivating device.
(1) Section 29.991(a)(1) now stipulates that a single tuel pump failure should not jeopardize the capability of the fuel system from delivering the fuel necessary to satisfy the requirements of § 29.955. This stipulation excludes any fuel pumps that are approved as a part of the type certificated engine.
(2) Section 29.991(a)(2) expands the stipulation of § 29.991(a)(1) by including any component(s) required to drive the fuel pump (such as electric motors or generators for electric pumps). This section also stipulates that if the pump is engine driven, failure should not affect more than the engine served by the pump.
b. Procedures. The method of compliance for this section is unchanged.
484. § 29.993 FUEL SYSTEM LINES AND FITTINGS.
a. Explanation. This rule outlines design requirements for fuel system lines.
b. Procedures.
(1) Compliance is usually obtained by employing routing and clamping as described in Paragraph 709, Chapter 14, Section 2, of AC 43.13-1A and by monitoring the arrangement throughout the developmental and certification test period.
Requirements for approved flexible lines may be resolved by utilizing lines listed as TSO C53a approved for installation in either normal or high temperature areas as appropriate.
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(2) Verify adequate clearance exists between lines and elements of the rotorcraft control system at extremes of control travel, including control deflections and, for flexible lines (hoses), possible variations in routing.
(3) Flexible lines inside fuel or oil tanks require special evaluation to assure that the external surfaces of these lines are compatible with the fluids involved and that fluid sloshing will not cause line failure. Lines inside tanks should be routed to avoid impingement by fuel or oil filler nozzles.
(4) Good design practice suggests that all flammable fluid lines should be routed to minimize the possibility of rupture in the event of a crash or from engine rotor disc failure.
485. § 29.995 (Amendment 29-13) FUEL VALVES.
a. Explanation. This regulation requires that fuel valves be supported so that no loads resulting from their operation or from accelerated flight conditions are transmitted to the lines attached to the valve.
b. Procedures. Compliance with this rule is usually accomplished by designing the installation of the fuel valve so that the valve is supported by either primary or secondary airtrame structure.
486. § 29.997 (Amendment 29-10) FUEL STRAINER OR FILTER.
a. Explanation. This rule provides for a main in-line fuel filter designed to collect all fuel impurities which could adversely affect fuel system and engine components downstream of the filter. The rule also requires a sediment bowl and drain (or that the bowl be removable for drain purposes) to facilitate separation of contaminations, both solid and liquid, from the fuel.
b. Procedures.
(1) The filter should be mounted in a horizontal segment of the fuel line to facilitate proper action of the sediment bowl. If the filter is located above the fuel tank, it becomes necessary to activate a fuel boost pump to achieve positive drainage of the filter bowl. Without pump pressure, air may enter the fuel system during the filter draining operation and, for turbine engines, result in transient power surges or engine failure during subsequent engine operation. A flight manual note to require pump(s) to be "on" during filter draining would be appropriate.
(2) Section 29.997(d) sets forth a requirement for filter capacity and for filter mesh. The capacity requirement may be substantiated by showing that the filter, when partially blocked by fuel contaminates (to a degree corresponding to the indicator marking or setting required by § 29.1305(a)(17)), does not impair the ability of the fuel Par 484 777
system to deliver fuel at pressure and flow values established as minimum limitations for the engine. The filter mesh must be sized to prevent passage of particulate which cannot be tolerated by the engine. FAR Part 33 requires that the degree and type of filtration be established. This information should be the base for selecting the filter mesh. Although a test may be devised and conducted, data from the filter manufacturer usually are acceptable to verify compliance. Note that when the filter capacity is reached, continued flow of contaminated fuel may result in engine failure. A flight manual note regarding precautionary procedures is appropriate.
(3) FAR Part 33 (through Amendment 33-6) has an identical requirement for a fuel filter for engine fuel systems; however, it is not intended that two filters should be required.
486A. § 29.997 (Amendment 29-26) FUEL STRAINER OR FILTER.
a. Explanation. Amendment 29-26 requires that a fuel strainer or filter should be installed between the fuel tank outlet and the first fuel system component that is susceptible to fuel contamination. Components that will be protected from contamination include but are not limited to fuel metering devices which control flow rate, fuel heaters, and positive displacement pumps. The amendment also requires a sediment bowl and drain (unless the bowl is readily removable for drain purposes) to facilitate separation of solid and liquid contaminants from the fuel.
b. Procedures.
(1) The fuel strainer or filter should be accessible for draining and cleaning. It should incorporate a screen or other element that is easily removable. It should be mounted so that its weight is not supported by the inlet or outlet connections of the strainer itself, unless it can be shown that adequate strength margins exist in the lines and connections.
(2) The fuel strainer or filter should have a sediment trap and drain (unless the trap is readily removable for drain purposes). The volume capacity of the sediment trap is specified in § 29.971(a) (0.10 percent of the tank capacity or 1/16 of a gallon).
(3) The fuel strainer or filter mesh should provide the filtration stipulated in the FAA/AUTHORITY-approved engine installation manual that is prepared for the type certificated engine (FAR Part 33).
(4) The fuel strainer or filter should have the capability to remove any contaminant that would jeopardize the flow of fuel that is necessary to meet the requirements of § 29.955. In addition, the strainer or filter should have a bypass system with an impending bypass indicator (Refer to § 29.1305(a)(17)). When the strainer or filter is partially blocked with contaminants, to the degree that the fuel flow requirements of § 29.955 can no longer be achieved, the impending bypass indicator 778 Par 486
should be activated. At this point, the strainer or filter should not yet be bypassing unfiltered fuel. Although a test may be devised and conducted, data from the filter manufacturer usually are acceptable to verify compliance. Note that when the filter capacity is reached, continued flow of contaminated fuel may result in engine failure. A flight manual note regarding precautionary procedures is appropriate.
(5) Section 33.67(b) has an identical requirement for a fuel filter for engine fuel systems; however, it is not intended that two filters should be required.
487. § 29.999 (Amendment 29-12) FUEL SYSTEM DRAINS.
a. Explanation. This regulation provides for fuel system drains and defines the requirements which the system must meet.
b. Procedures.
(1) The location and function of the fuel system drains are an integral part of any fuel system. There may be several drains required dependent upon the fuel system design. Each fuel tank sump and certain types of fuel strainers or filters require a means to drain (reference §$ 29.971 and 29.997).
(2) Selection of the location and orientation of the drain discharge in the design phase is important to assure that there is no impingement on any part of the rotorcraft.
To show compliance with the requirement may require tests dependent upon whether the applicant has a previously approved design which is similar, or if the system is a new design for which no previous experience is available.
(3) The location of the drain valve should be selected so that the requirements for accessibility, ease of operation, and protection are met.
(4) Advisory Circular 20-119 provides an acceptable means, but not the only means, of compliance with the requirement for positive locking of fuel drain valves in the closed position.
(5) The fuel drain installation on aircraft with retractable landing gear will be satisfactory if recessed within the outside surface of the aircraft.
487A. § 29.999 (Amendment 29-26) FUEL SYSTEM DRAINS.
a. Explanation. Amendment 29-26 adds the requirement that fuel system drains be effective with the rotorcraft in any allowable ground attitude including uneven terrain.
In addition, the change amended § 29.999(b)(2) to require fuel drains have a means to ensure positive closure as contrasted to positive locking when in the "off" position. This will accommodate designs featuring spring-loaded drain closures that have been found to be satisfactory.
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b. Procedures. All of the policy material pertaining to this section remains in effect. Additionally, selection of the location and orientation of the fuel drain discharge in the design phase is important to assure that there is no impingement upon any part of the rotorcraft. The location and orientation should also ensure effective fuel drainage when the rotorcraft is parked on uneven terrain. To show compliance with the requirement, tests may be required, dependent upon whether the applicant has a previously approved design that is similar, or the system is a new design for which no previous experience is available.
488. § 29.1001 (Amendment 29-26) FUEL JETTISONING.
a. Explanation. Amendment 29-26 adds § 29.1001 to set forth the certification requirements for a fuel jettisoning system if it is installed in the rotorcraft.
b. Procedures. In showing compliance with the requirements of § 29.1001, the following guidance is provided.
(1) The fuel jettison system should be demonstrated to be safe in all normal flight regimes. Takeoff, hover, and in-ground-effect maneuvers may be excluded if appropriate limitations are prescribed.
(2) The fuel jettison system, and its operation, should be shown to be free from fire hazard. If possible, the fuel should discharge clear of any part of the rotorcraft;
however, it should be shown that any fumes or fuel, that do impinge upon the rotorcraft in the form of a fine mist, does not form droplets that run along the exterior structure and enter any part of the rotorcraft (wheel wells, cargo area, tail boom, etc.). It should also be shown that jettisoned fuel is not ingested by the engines or the auxiliary power unit (APU). This demonstration can be conducted by jettisoning a glycol based, dye colored fluid and noting the pattern displayed on a dye sensitive coating applied to the rotorcraft exterior. The demonstration should be conducted over all flight regimes in which system operation is permitted. The demonstration should also take into account the maximum rate of descent and all airspeeds where fuel impingement upon the fuselage would most likely occur. Rotorcraft controllability should remain satisfactory throughout the fuel jettisoning operation and should also be demonstrated.
(3) The requirements in § 29.1001(c) were established to prevent complete fuel depletion and provide the capability to effect continued safe flight and landing.
(4) The controls for the fuel jettison system should be designed so that a "minimum" flight crew can perform the jettison operation and be able at any time to stop the jettison process or begin it again. These design requirements give the flight crew the capability and flexibility to manage their on-board resources.
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(5) The requirements of § 29.901(c) are intended to emphasize that no single failure or malfunction or probable combination of failures of the fuel jettisoning system will jeopardize the safe operation of the rotorcraft.
(6) If the rotorcraft has an auxiliary fuel tank, an auxiliary fuel jettisoning system may be installed to jettison the additional fuel provided the jettisoning system has separate and independent controls and it also meets all of the requirements of this section.
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489.-497. RESERVED.
intentionally Left Blank 782 (thru 790) Par 489
SEÇTION 28. OIL SYSTEM.
498. § 29.1011 GENERAL.
a. Explanation.
(1) The oil system provided for each installed engine should provide all of the lubrication required by the engine and supply it at a temperature which is within the operating temperature limits established for that engine when it was certified.
(2) The usable oil capacity of each oil system should be sufficient to provide oil to the engine at the maximum oil consumption limit of the engine under critical operating conditions. All circulating requirements and operating temperature limits for the oil should be met.
b. Procedures.
(1) There are three basic engine oil supply and cooling system concepts that are used. There are self-contained systems (a complete system certified with the engine), systems that have both engine and airframe components, and systems that are totally supported by airframe components. Any one of these three concepts can be used to meet the requirement of having an independent oil system for each engine.
(2) Oil tank capacity is primarily determined by the engine's oil consumption rate. Other factors which should be considered when sizing the oil supply system are the endurance of the rotorcraft under critical operating conditions, and the amount of oil circulating in the system to maintain proper cooling. Adequacy of the engine oil supply system can be shown by analysis supported by engine oil consumption and cooling system data. For reciprocating engines, the ratio of one gallon of oil for each 40 gallons of fuel can be used; however, an oil-fuel ratio lower than 1:40 can be used if properly substantiated by oil consumption data on the engine.
(3) The engine oil cooling requirements are defined in §§ 29.1041 through
29.1049. The design of the engine oil cooling system will be influenced by hot day conditions, by the engine heat rejection rate, and other oil system operating data provided by the engine manufacturer. Sizing of the oil cooler will depend upon the engine data and whether the oil cooler will also be used for main transmission oil cooling. Oil cooler size should be kept as small as possible due to its effect on rotorcraft structure, but in all cases, adequate cooling should be demonstrated throughout the operating envelope of the rotorcraft.
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499. § 29.1013 (Amendment 29-10) OIL TANKS.
a. Explanation. This regulation identifies the requirements that each oil tank must meet. It also specifies that the oil tank installation must meet the installation requirements of § 29.967.
b. Procedures.
(1) The oil tanks usually are constructed of aluminum, aluminum alloy, or stainless steel and are of such a design to permit installation in the aircraft as close to the engine as the design allows. The choice of materials will generally be determined by the selected location of the tank. The tank envelope or outline will generally be determined by the location within the structure of the rotorcraft.
(2) The design of the tank is required to meet the expansion space requirements as specified in the regulation for the particular installation. This is generally accomplished by locating the filler cap in such a manner that the expansion space cannot be inadvertently filled with the rotorcraft in normal ground attitude.
(3) The tank is required to be properly vented and the vent requirements are identified in the regulation.
(4) Unless alternate means are provided, it is good design practice to locate the oil tank with respect to the engine so that when the rotorcraft is in its normal ground attitude, a positive head to the oil pump inlet is provided.
(5) Sections of the regulation address specific requirements when Category A certification is requested.
(6) The designer should be aware of the requirements associated with the location of the oil tank outlet and the marking requirements specified in § 29.1557(c)(2).
(7) Flexible oil tank liners may be used; however, they must be approved or shown to be suitable for the particular installation.
(8) An "external oil system" which is defined as being those components, lines, etc., of an oil system which are outside the engine and not supplied as part of a certificated engine. The components of such a system which are within the fire zone and required to be fire resistant. Those outside the fire zone need not be fire resistant.
500. § 29.1015 (Amendment 29-10) OIL TANK TESTS.
a. Explanation. This regulation defines the tests that must be accomplished to show compliance for rotorcraft oil tanks.
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(1) The oil tank should be designed and installed so that it can withstand, without failure, any vibration, inertia, and fluid loads to which it may be subjected in operation.
(2) The installation should meet the requirements of § 29.965 except that for pressurized tanks used with turbine engines, the test pressure may not be less than 5 PSI plus the maximum operating pressure of the tank. For all other tanks, the test pressure may not be less than 5 PSI.
b. Procedures. The pressure tests require that 5 PSI plus operating pressure but in any case no less than 5 PSI be used to substantiate the oil tank. To accomplish these tests, the various tank openings are sealed. An adapter fitting is fabricated by which regulated, pressurized air is introduced into the tank. This air pressure is measured by means of a calibrated air pressure gauge. Any of several methods to determine whether the tank is leaking may be used. As an example, if the tank is relatively small, emergence in a tank of water may be used. Other means such as applying soapy water to the joints are also satisfactory. In any respect, the leak check using test fluid conforming to Federal Specification TT-S-735, Type III, may also be used.
501. § 29.1017 OIL LINES AND FITTINGS.
a. Explanation. This regulation outlines the certification requirements for oil lines and fittings.
b. Procedures. The oil system lines and fittings are required to meet the requirements of § 29.993; therefore, the routing and clamping described in Paragraph 709, Chapter 14, Section 2, of AC 43.13-1A may be utilized as guidance for the system design. An evaluation carried out through the development and certification test period will usually surface any problems of interference and/or vibration.
(1) When flexible hoses are used in the lubrication system they must be substantiated. Hoses listed in TSO C53a may be used which would preclude certain substantiation requirements.
(2) Location of the breather lines and discharge should be carefully evaluated to determine that the requirements of this paragraph are followed.
(3) The routing of fluid lines should be such that drooping lines and fluid traps which are undrainable are avoided.
502. § 29.1019 (Amendment 29-10) OIL STRAINER OR FILTER.
a. Explanation. This regulation defines the requirements for the engine oil system strainer or filter. If a strainer or filter which meets the requirements of this paragraph is Par 500 793
incorporated as part of the type certificated engine, an additional airframe filter is not required.
b. Procedures. This paragraph requires an oil strainer or filter through which all of the oil flows for each turbine engine installation. The strainer or filter should be sized to allow oil flow at the flow rates and within the pressure limits as specified in the engine requirements. The effect of oil at the minimum temperature for which certification is sought should be accounted for.
(1) For each oil strainer or filter required by § 29.1019(a) which has a bypass, the bypass should be sized to allow oil flow at the normal rate through the oil system with the filtration means completely blocked.
(2) For each oil strainer or filter installed per this rule, the capacity must be such that the oil flow and pressure are within the operating limits established for the engine. The mesh requirements are determined by the engine specification for the filtration of particle size and density.
(3) Section 29.1019(a)(3) requires an indicator that will show when the contaminant level of the filtration system, as specified in § 29.1019(a)(2), has been reached. The indicator should signal a contaminant level which has not caused the filter to go into a bypass condition. Consideration should also be given so that the contaminant level at which the indicator is activated is such that the filter would not bypass during a flight time based on full fuel at a cruise condition with the lubricant contaminated to the degree used to show compliance with § 29.1019(a) (2).
(4) An evaluation of the construction and location of the bypass associated with the strainer or filter should be accomplished. The appropriate installation of the filter based on this evaluation would preclude the release of the collected contaminants in the bypass oil flow.
(5) If an oil strainer or filter installed in compliance with this regulation does not have a bypass, there must be a means to connect it to the warning system required in § 29.1305(a)(18). This warning should indicate to the pilot the contamination before it reaches the capacity established in § 29.1019(a)(2). Section 29.1019(b) covers the blocked oil filter requirements associated with reciprocating engine installations. The lubrication system should be such that the normal oil flow will occur with the filter completely blocked.
502A. § 29.1019 (Amendment 29-26) OIL STRAINER OR FILTER.
a. Explanation. Amendment 29-26 relaxes the requirements of § 29.1019(a)(3) from requiring an indicator to indicate the contamination level of oil filters. The rule change allows acceptance of a "means to indicate" the contaminate level to allow a wider range of acceptable methods of compliance.
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