(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 27.997(d) sets forth a requirement for filter capacity. 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 § 27.1305(a)), does not impair the ability of the fuel 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 matter which cannot be tolerated by the engine. Part 33 requires that the degree and type of filtration be established for the engine. This information, available in the FAA/AUTHORITY-approved Engine Installation Manual, should be the basis for selection of the airframe 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) 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. § 27.997 (Amendment 27-23) FUEL STRAINER OR FILTER.
a. Explanation. Amendment 27-26 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.
644 Par 486
(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 § 27.971(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 § 27.955. In addition, the strainer or filter should have a bypass system with an impending bypass indicator (Refer to § 27.1305(a)(17)). When the strainer or filter is partially blocked with contaminants, to the degree that the fuel flow requirements of § 27.955 can no longer be achieved, the impending bypass indicator 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. § 27.999 (Amendment 27-11) 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 §$ 27.971 and 27.997).
(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.
Par 486A 645
АС 27-1A 7/30/97
(4) Spring-loaded fuel drain valves conforming to MIL-V-25023B, TSO-C76, or equivalent, may be approved as "positive locking" valves for those installations where the person operating the valve can visually confirm that the valve is closed, provided the applicant has shown that the valve will not open inadvertently under any foreseeable operating condition.
487A. § 27.999 (Amendment 27-23) FUEL SYSTEM DRAINS.
a. Explanation. Amendment 27-23 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 § 27.999(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.
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.-497. RESERVED.
646 (thru 656) Par 487
SECTION 28. OIL SYSTEM.
498. § 27.1011 (Amendment 27-23) GENERAL.
a. Explanation.
(1) This regulation defines the general oil system requirements for the engine.
(2) Each engine oil system should be independent of the system for the other engine(s).
(3) The minimum acceptable usable oil capacity, in terms of rotorcraft endurance and engine maximum oil consumption, is specified.
(4) The oil cooling provisions should be capable of maintaining the oil inlet temperature at or below the maximum allowable value.
b. Procedures.
(1) The requirement for an independent oil system for each engine should ensure continued adequate lubrication of each engine in the event of failure of the opposite engine(s) or of that opposite engine's oil system. The provision does not require that the engine oil system be independent of other components; e.g., the use of the engine's oil system for rotor drive system component lubrication is not precluded by this regulation.
(2) The usable oil capacity for each engine's oil system should not be less than the product of the maximum endurance of the rotorcraft times the engine's maximum oil consumption, plus some margin to ensure adequate circulation and cooling.
(3) Instead of a rational analysis of rotorcraft endurance and engine oil consumption rate, a usable oil capacity of 1 gallon for each 40 gallons of usable fuel may be used. (This concept should apply only to reciprocating engines.)
(4) Flight tests should be required to show adequate oil cooling provisions (reference § 27.1041).
499. § 27.1013 (Amendment 27-9) OIL TANKS.
a. Explanation. This regulation, along with § 27.1015, defines the oil tank design and installation requirements.
(1) The oil tank should be designed and installed to withstand, without failure, any vibration, inertia, fluid, and structural loads expected in operation.
Par 498 657
(2) For reciprocating engines, the expansion space should not be less than
0.5 gallons or 10 percent of the tank capacity, whichever is greater.
(3) For turbine engines, the expansion space should not be less than 10 percent of the tank capacity.
(4) It should not be possible to inadvertently fill the expansion space with the rotorcraft in the normal ground attitude.
(5) Adequate venting should be provided.
(6) Oil overflow from the filler opening into the oil tank compartment should be prevented.
b. Procedures.
(1) The structural analysis of the tank, including the attachments, should ensure that the tank will not leak under the vibration, inertia, fluid, and structural loads expected in service.
(2) The expansion space may be determined by calculating the difference between the volume up to the vent opening and the volume to the spillover level of the filler opening. The expansion space volume must not be less than 10 percent of the volume to the filler spillover level (tank capacity) or not less than 0.5 gallons for reciprocating engine installations with oil tank capacities of 5 gallons or less.
(3) To assure adequate venting under all normal flight conditions, the tank should be vented from the top portion. Traps where condensed water vapor might freeze and obstruct the vent line should be avoided. If other components, perhaps an engine speed reduction gearbox, are vented to the engine oil tank, the oil tank vent line should be sized to handle this additional requirement as well as the air normally entrained in the return oilflow from the engine.
(4) A suitable method to prevent oil spillover from the filler opening from entering the compartment containing the oil tank would be a scupper with an attached drain line that discharges clear of the rotorcraft.
500. § 27.1015 (Amendment 27-9) OIL TANK TESTS.
a. Explanation. This regulation specifies the requirements which the oil tank tests should verify. Each oil tank should withstand, without leakage, an internal pressure of 5 PSI. This regulation also specifies that each pressurized oil tank used with a turbine engine must withstand, without leakage, an internal pressure of 5 PSI plus the maximum operating pressure of the tank.
658 Par 499
b. Procedures. Test procedures for demonstrating these requirements are relatively simple and straightforward. Suitable adapters are fabricated to seal the various tank openings and also a fitting to introduce pressurized air into the tank. The air source needs to be regulated, and a suitable pressure gauge with a current calibration is required. Appropriate methods to check for leakage should also be available. This leak check can be a dip tank, soap and water mixture, or any other method which will provide acceptable results. Test fluid conforming to Federal Specification TT-S-735, Type III, or equivalent, is also an acceptable leak check substance.
501. § 27.1017 OIL LINES AND FITTINGS.
a. Explanation. This regulation outlines the certification requirements for oil lines and fittings.
b. Procedures.
(1) The line should be supported to prevent excessive vibration, and flexibility should be provided between points of relative motion. Advisory Circular 43.13-1A, Chapter 14, Section 2, Paragraph 709, may be used as guidance for the system design.
(2) Flexible hose must be approved. Generally, hoses listed in TSO-C53a or those qualified to equivalent military standards are accepted.
(3) The engine inlet and outlet oil lines should not have an inside diameter less than the corresponding inside diameter of the engine connection, and no line splices are permitted between connections; however, larger lines may be needed to ensure adequate oil flow to the engine or the transmission. Oils which exhibit high viscosity, long oil lines, and arrangements with little or no elevation of the tank outlet with respect to the engine inlet, are design characteristics which should be carefully checked.
502. § 27.1019 (Amendment 27-9) 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 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.
Par 500 659
(1) For each oil strainer or filter required by § 27.1019(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 when operating with oil contaminated to a degree greater than established during engine certification, the oil flow and pressure are within the operating limits established for the engine. The mesh requirements are determined by the engine installation documents for the filtration of particle size and density.
(3) Unless the filter is located at the oil tank outlet, § 27.1019(a) (3) requires an indicator that will show when the contaminant level of the filtration system, as specified in § 27.1019(a) (2), has been reached. The indicator should signal a contaminant level which will allow completion of the flight before the filter would enter a bypass condition.
The indicator may be a pop-out button or other maintenance cue that is checked on each preflight.
(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 tlow.
(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 § 27.1305(r). This warning should indicate to the pilot the contamination before it reaches the capacity established in § 27.1019(a)(2).
(6) Section 27.1019(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. § 27.1019 (Amendment 27-23) OIL STRAINER OR FILTER.
a. Explanation. Amendment 27-23 relaxed an unduly restrictive requirement for 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.
•b. Procedures. All of the policy material pertaining to this section remains in effect except that an "indicator" is not required to indicate the contamination level of the oil filters. Unless the filter is located at the oil tank outlet, § 27.1019(a)(3) requires that the oil strainer or filter have the means to indicate when the contaminant level of the filtration system, as specified in § 27.1019(a)(2), has been reached. If an indicator is installed, it should signal a contaminant level that will allow completion of the flight 660 Par 502
before the filter reaches a bypass condition. The indicator may be a pop-out button or other maintenance cue that is checked on each preflight inspection.
503. § 27.1021 OIL SYSTEM DRAINS.
a. Explanation. This regulation requires provisions be provided for safe drainage of the entire oil system with the rotorcraft at normal ground attitude and defines certain requirements for assuring that no inadvertent oil flow occurs from the system provided.
b. Procedures.
(1) The design of the oil system must provide a means for safe drainage of the entire oil system. This may require one or more drains depending on the design of the system. The routing of fluid lines should be such that drooping lines and fluid traps which are undrainable are avoided.
(2) The drain(s) must provide a means for a positive lock in the closed position.
The method by which the lock is accomplished may be manual or automatic.
504. § 27.1027 (Amendment 27-23) TRANSMISSION AND GEARBOXES:
GENERAL
a. Explanation. Amendment 27-23 adds a new § 27.1027. This new section provides the regulations for rotorcraft transmission and gearbox lubrication systems. It incorporates lubrication system requirements that were derived from existing engine oil system requirements. These additional requirements have been adjusted or modified to reflect the needs of transmissions and gearboxes. Transmission and gearbox lubrication system regulations are similar to those for engines; therefore, reference is made to the engine lubrication sections as applicable.
b. Procedures.
(1) The pressure lubrication systems for rotorcraft transmissions and gearboxes should comply with the same requirements as the engine lubrication systems stipulated in §§ 27.1013 (except Paragraph 27.1013(c)), 27.1015, 27.1017,
27.1021, and 27.1337(d). These sections provide the requirements for oil tanks, tank tests, oil lines and fittings, and oil system drains.
(2) Each pressure lubrication system for rotorcraft transmissions and gearboxes should have an oil strainer or filter. The strainer or filter should:
(i) Remove any contaminants from the lubricant which may damage the transmission, gearbox, or other drive system component and any contaminants that may impede the lubricant flow to a hazardous degree.
Par 502 A 661
(її) Be equipped with a means to indicate that the bypass system (required by § 27.1027(b)) is at the point of opening due to the collection of contaminants on the strainer or filter, and;
Be equipped with a bypass system that will permit lubricant to continue to flow at the normal rate if the strainer or filter is completely blocked. In addition, the bypass system should be designed so that contaminants that have collected on the filter will not enter the bypass flow path when the system is in the bypass mode.
(3) Section 27.1027(c) requires a screen at the outlet of each lubricant tank or sump that supplies lubrication to rotor drive systems and rotor drive system components. The screen should remove any object that might obstruct the flow of lubricant to the filter required by § 27.1027(b). The requirements of § 27.1027(b) do not apply to the tank outlet screen.
(4) Splash-type lubrication systems for rotor drive system gearboxes should comply with §§ 27.1021 and 27.1337(d).
662 Par 504
505.-515. RESERVED.
Intentionally Left Blank Par 505 663 (thru 673)
SECTION 29. COOLING
516. § 27.1041 (Amendment 27-2) GENERAL
a. Explanation. The rotorcraft design should provide for cooling to maintain the temperature of all powerplant and power transmission components and fluids within the limitations established for the items. Cooling provisions should be adequate for shutdown and for water, ground, and flight operating conditions. The adequacy of the cooling provisions should be demonstrated by flight testing.
b. Procedures.
(1) Test conditions and procedures necessary to demonstrate adequate cooling for water, ground, flight, and shutdown conditions should be agreed upon between the applicant and the FAA/AUTHORITY certification engineer. A cooling test proposal which defines the agreed test points and procedures should be prepared well in advance of the official certification testing.
(2) The test conditions selected would typically include climb, cruise, hover, and shutdown after a prolonged hover. Hover OGE should be evaluated if sling load operation is envisioned for the rotorcraft. One test condition which should be examined, particularly with regard to transmission cooling, is the point of highest multiengine mechanical power at the maximum ambient temperature. This is identified as test point "A" in Figure 516-1. The selection of test points should be tempered with engineering judgment and based on results from similar aircraft if such data are available. In showing compliance with the cooling requirements, the applicant should not be required to exceed rotorcraft established limits (gross weight, drive system torque, measured gas temperature, etc.), aircraft power required, or power available.
The applicant may elect, however, to exceed these limits in order to minimize test points by conservative testing, or to anticipate future growth (increased gross weight, etc.).
(3) The need for a comprehensive cooling test plan prior to certification testing cannot be overemphasized. Highly derated engine installations, the relationship of power required to power available, the use of bleed air devices which would increase the measured gas temperature while aircraft power required remains the same, auxiliary cooling provisions, and the increase in engine temperatures with engine deterioration are factors which could affect the selection of cooling demonstration test points.
674 Par 516
MULTIENGINE POWER AVAILABLE 20K -
HOT DAY - 15K - XMSN LIMIT PRESSURE ALTITUDE OAT 10° C 10K 15° C 20° C 25° C 30° C 35° C POWER POINT "A" FIGURE 516-1 ADDITIONAL COOLING TEST POINT Par 516 675