7130/97 AC 29-2B considered in the design and structural substantiation. MIL-HDBK-5D contains material allowables versus temperature data for a wide variety of metallic engineering materials.
(3) For compliance with § 29.1123(c), the piping and its restraint system should be designed to minimize loading induced on the piping by the relative motion (in-service deflections) of the components to which the system attaches. Isolation of significant deflection induced loading (if required based on analysis and strain surveys) by use of flexible joints or other equivalent devices or designs should be considered. Any such in-line device used to reduce deflection loading should be fireproof and leak free when performing its intended function.
(4) For critical load case determination, the expansion-induced thermal loading should be added in with mechanical relative-motion induced loads and internal exhaust gas flow loads to provide total critical loads for both a proper static and a proper fatigue structural substantiation. The critical combined static load should be compared with the emergency impact loads of § 29.561(Paragraph b(2)) to determine the critical design load case for static strength substantiation.
(5) It should be noted that the majority of the exhaust piping verification testing required for certification can be accomplished during the rotor drive system tie down testing of § 29.923.
550. § 29.1125 (Amendment 29-12) EXHAUST HEAT EXCHANGERS.
a. Explanation. This section applies only to rotorcraft powered by reciprocating engine(s) or equipped with reciprocating auxiliary propulsion units (APU). This regulation states the certification requirements for exhaust heat exchangers (EHE's) which are summarized as follows:
(1) § 29.1125(a) requires that each EHE be constructed and installed to withstand vibration, inertia and other operational loads.
(2) § 29.1125(a)(1) requires that each EHE be able to operate continuously at the highest anticipation service temperature.
(3) § 29.1125(a)(1) requires that each EHE be corrosion resistant to exhaust gases and other corrosion sources.
(4) § 29.1125(a)(2) requires that each EHE have provisions for inspecting its critical parts and areas.
(5) § 29.1125(a)(3) requires that each EHE have cooling provisions where it is subjected to hot exhaust gases.
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(6) § 29.1125(a)(4) requires that each EHE muff design eliminate stagnation areas or liquid traps that would contribute to ignition of leaked flammable fluids.
(7) § 29.1125(b) requires that each EHE used to heat ventilating air for occupants-- Either have a secondary heat exchanger between the primary EHE and the ventilating air system; or (її) Have other equivalent means to prevent harmful contamination of ventilating air.
b. Procedures. HE's and their installations are typically certified by analysis and installation tests conducted during the basic certification process, including flight tests or simulated flight tests, as tollows:
(1) Because of their durability in the hot exhaust environment, EHE's are usually constructed from stainless steel or alloy steel of the appropriate structurally and thermally derived wall thickness. The EHE and its system should be designed to expand freely to minimize thermal expansion (thermal strain) induced loads on the EHE and its restraint system. If thermal expansion induced loads (in conjunction with deflection induced loads and exhaust flow loads) are significant relative to the limit load of the EHE or its attachments, a fatigue check on critical design points) should be performed. The fatigue check should establish a safe life or an approved limited life for the critical components) in the EHE system.
(2) EHE's should be properly supported so that the maximum loads anticipated in service are properly distributed and reacted and so that thermal-expansion-induced loading is minimized. Typically, the worst-case static design load conditions are either the emergency impact loads acting alone (reference § 29.561), or the critical combination of loads from thermal expansion, in-flight deflections and internal exhaust gas flow. Several combinations of these loads should be examined to determine the critical combination. The EHE should be supported and restrained so that critical frequencies are avoided and the induced vibration environment is minimized. Flight tests or bench tests, such as vibration surveys conducted during rotor system endurance testing, may be necessary in some cases, to properly define or validate the vibration environment and EHE's critical modes and their effect on EHE design.
Operating modes such as ground idle, flight idle, 40 percent and 80 percent of maximum continuous power, maximum continuous power, OEI power settings, and other critical power settings should be investigated to determine their vibratory effect on the EHE system. The strength reduction of EHE materials at operating temperature and at critical temperatures should be properly considered in EHE design and structural substantiation (MIL-HDBK-5D contains material allowables versus temperature data for a wide variety of metallic engineering materials). The EHE and its restraint system should be designed to minimize loads induced by the relative motion (in-service 860 Par 550
deflections) of the components to which the EHE attaches. Isolation of significant-deflection-induced loading (as required, based on analysis and strain surveys) by use of flexible joints, other equivalent flexible devices, or designs should be considered. Any such in-line device used to reduce deflection loading should meet applicable certification requirements and be leak-free.
(3) Expansion analysis and verification tests of the EHE should be conducted to ensure its thermal (and structural) integrity and to ensure that thermal expansion does not cause the EHE to contact (or come close to) ambient temperature aircraft materials, structure or system components and either create a fire hazard or an unintended reduction in strength. To ensure that expansion analyses and tests are properly conducted, the maximum in-service temperature excursion should be properly defined. The maximum temperature excursion should be based on the maximum temperatures of the EHE and exhaust gases, as affected by the insulatory characteristics of the EHE's enclosure, and as affected by a worst-case hot day. The worst-case temperature environment used for analysis can be verified by a temperature survey which, when run on cooler days, can be adjusted to the worst-case hot day environment using methods identical to those used for engine cooling tests (reference Paragraph 517, Cooling Tests).
(4) Hot aircraft exhaust gases are very corrosive; thus, proper material selection and corrosion protection design should be performed and validated during certification. Advisory Circular (AC) 43-4, "Corrosion Control For Aircraft" contains a detailed discussion of exhaust gas corrosion problems. The in-service corrosive environment should be identified and characterized as thoroughly as possible by chemical analysis, tests and service experience. Once defined, appropriate design techniques and materials should be selected. Certification tests may be required to ensure proper substantiation. Phased inspections and inspectability should be considered (reference (4)).
(5) The EHE's design should be reviewed for inspectability to ensure that structural and thermal integrity is maintained over the intended life of the EHE. Also, if the design review is not conclusive relative to inspectability, a tear down inspection should be conducted.
(6) Each EHE design should be reviewed, analyzed, and tested to ensure that cooling provisions are adequate where EHE surfaces are subjected to hot exhaust gases. This is necessary to prevent hazardous hot spots or a burn through which may cause a fire and contaminate the occupied environment.
(7) Each EHE design should be reviewed, analyzed, and tested to ensure that stagnation areas and liquid traps do not exist. This can be done using bench flow tests.
These stagnant areas and traps could become ignition sources if wetted with a leaking flammable fluid. A review of potential leaking flammable fluid hazards should be Par 550 861
conducted and appropriate preventative measures such as drains and drip fences installed to ensure they are routed away from EHE's.
(8) Each EHE design which will be used to heat ventilating air for occupants should be reviewed to ensure that the EHE is a double walled system, (i.e., it would require failure of two EHE surfaces to allow toxic exhaust gases to intermix with cabin ventilating air). Each EHE wall should be designed with equal thermal and structural resistance since a single undetected inner wall failure would subject the outer wall to the primary heat load. Also, inspectability provisions should be provided or means identified to ensure that inner wall failures can be detected in service. Any equivalent means which is applied for must clearly provide an equivalent level of safety to a double walled EHE.
551.-560. RESERVED.
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SECTION 32. POWERPLANT CONTROLS AND ACCESSORIES
561. §. 29.1141 (Amendment 29-13) POWERPLANT CONTROLS: GENERAL.
a. Explanation.
(1) Section 29.1141(a) References §§ 29.777 and 29.1555. The detailed compliance procedures for powerplant control arrangement and markings are found in these sections.
(2) Section 29.1141(b) requires that controls be located and/or shielded such that normal movement of cockpit personnel will not cause inadvertent control movements.
(3) Section 29.1141(c) requires that each flexible control (push-pull cables) be properly approved.
(4) Section 29.1141(d) requires that each control maintain its set position without movement from an inadvertent source such as vibration or control system loads. This is required so that constant flightcrew attention is not necessary.
(5) Section 29.1141(e) requires that each control be able to withstand operating loads without excessive deflection. Excessive deflection is interpreted to be that deflection that would cause erratic movement, lack of crispness, or premature failure.
(6) Section 29.1141(f) specifies acceptable open/close positions for manual valves to prevent power failure due to improper control valve positioning.
Power-assisted valves should have means to indicate to the flightcrew that the valve is either in the fully open or fully closed position or that the valve is moving between these two positions.
(7) The control system is subject to evaluation under § 29.901(c); i.e., for turbine installations, no single failure or malfunction, or probable combination thereof, of any powerplant control system should cause the failure of any powerplant function necessary for safety. One acceptable way to determine this is by use of a failure modes and effects analysis (FMEA).
b. Procedures.
(1) For compliance with § 29.1141(a), review the procedures for Paragraph 747 of this AC. Evaluation by the flight test pilot during the official flight test program is appropriate.
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(2) Compliance with § 29.1141(b) is normally evaluated during the flight test program and documented in the flight test report.
(3) Compliance with § 29.1141(c) may be accomplished by qualifying the control to MIL-C-7958, "Controls, Push-Pull, Flexible, and Rigid," or other approved standards or by previous approval in a similar function, installation, or arrangement.
(4) Compliance with § 29.1141(d) may be shown during the flight test program by monitoring the means to prevent control creep. This device or arrangement should be effective without crew attention and should not impose undue control displacement loads or interfere with accurate settings.
(5) Compliance with § 29.1141(e) may be shown by an appropriate structural analysis and/or a witnessed static load test using the factors specified under § 29.397 unless a lower value can be shown to be applicable. Operation tests and design details described in §§ 29.683 and 29.685 should also be considered.
(6) Compliance with § 29.1141(f)(1) may be accomplished by installing manual valves which have positive stops in the fully open and closed positions. The fuel valves, however, may have an arrangement to facilitate the capability of switching to different fuel tanks if suitable indexing is provided. Compliance with § 29.1141(f)(2) may be accomplished by installing a device which displays to the flightcrew one indication with valve fully open and another with the valve fully closed. Alternatively, an indication could be given when the valve is moving from fully open to fully closed with the indication ceasing when the valve position corresponds to the selected switch position (open or closed). An example would be a light that is "off" when the valve is fully open or fully closed and illuminates while the valve is transitioning.
562. § 29.1142 (Amendment 29.17) AUXILIARY POWER UNIT CONTROLS.
a. Explanation.
(1) This section addresses control requirements for any APU installed in a rotorcraft.
(2) The requirement for starting, stopping, and emergency shutdown of the APU from the flight deck is primarily to control APU operation in the event of improper operation or malfunction which could affect the safety of the aircraft.
b. Procedure.
(1) The requirements of this section apply to all APU installations in rotorcraft without regard to whether or not the APU is to be operated on the ground only, or operated in flight and on the ground.
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(2) The APU installation must provide sufficient controls to the flight crew to enable them to control the operation of the APU under normal and emergency conditions.
(3) Compliance can be shown by both demonstration and a failure analysis.
563. § 29.1143 (Amendment 29-12) ENGINE CONTROLS.
a. Explanation. This section prescribes safety standards applicable to arrangement and operation of the engine controls.
(1) Section 29.1143(a) requires a separate throttle for each engine.
(2) Section 29.1143(b) requires a throttle arrangement for control of all engines be achieved by:
Separate control of each engine.
(ii) Simultaneous control of all engines.
(3) Section 29.1143(c) requires that immediate actuation at the engine control should be provided by any given input at the cockpit throttle control.
(4) Section 29.1143(d) requires that each fluid injection system control (e.g., water-alcohol) other than the fuel system control must reside in the throttle controls.
This does not preclude the injection system pump from having a control located separately from the throttle.
(5) Section 29.1143(e) requires that power or thrust controls (that have fuel shut-off features) provide a means to prevent inadvertent movement to the shut-off position. This means should--
(i) Provide a positive lock or stop at the idle position; and
(il) Require a separate and distinct operation to place the control in the shut-off position.
b. Procedures.
(1) Certification data submitted by the applicant should be reviewed to ensure that all the design features stated in § 29.1143 exist.
(2) Proper engine control functioning (to verify the design features of § 29.1143) should be verified as part of the type inspection authorization (TIA) for the certification project.
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(3) Compliance with § 29.1143(e)(1) has been shown successfully in the past by use of idle detents (mechanical or electrical/mechanical such as a solenoid).
(4) In the past, compliance with § 29.1143(e) (ii) has been achieved by use of a switch or button to displace the idle stop or by use of distinct offsets in throttle motion to allow movement from the idle stop to shutoff.
563A. § 29.1143 (Amendment 29-26) ENGINE CONTROLS.
a. Explanation. Amendment 29-26 revises § 29.1143 by replacing the terms "throttle control" and "thrust control" with the more general term "power control." The changes should preclude misconceptions regarding engine control arrangements when governor-controlled turboshaft engines are employed in rotorcraft.
b. Procedures. The means of compliance for this section is unchanged.
563B. § 29.1143 (Amendment 29-34) ENGINE CONTROLS.
a. Explanation. Amendment 29-34 introduced the option of using 30-second/2-minute OEI power ratings to multiengine rotorcraft. This amendment revises § 29.1143 by adding the requirement for automatic control of 30-second OEI limits in the new Paragraph 29.1143(e). Automatic control of the 30-second OEl limits are required to prevent exceedances of the remaining power sections after the precautionary shutdown of one engine. The use of 30-second OEI power must be limited to emergency use only during flight conditions where one engine has failed or has been shutdown for precautionary reasons. During this critical stage of flight crew attention should not be focused on powerplant instruments to avoid limit exceedances.
b. Procedures. The automatic controls used to prevent 30-second OE limit exceedances can be installed on the airframe or the engine. The applicant should demonstrate that 30-second OEl limits that can affect the continued safe operation of the drive system or engine such as gas generator speed, measured gas temperature, torque, etc., cannot be exceeded. It should also be shown that these devices do not restrict the ability to achieve the full 30-second OEI limits. The operation of these limit devices can be demonstrated on the aircraft or if possible by using bench tests.
564. § 29.1145 (Amendment 29-13) IGNITION SWITCHES.
a. Explanation.
(1) This section addresses the arrangement and protection of ignition switches for reciprocating engines or for turbine engines which require continuous ignition.
876 Par 563
(2) The objective is to provide a means to shut off all ignition quickly, if required, while at the same time providing protection against inadvertent ignition switch operation.
(3) Section 29.1145(b) does not specifically state that turbine engines not requiring continuous ignition are excluded from the rule, but no benefit is realized by the capability of shutting off all ignition to these engines.
b. Procedures.
(1) Section 29.1145(b) is self-explanatory in specifying that a means be available to shut off all ignition quickly by the grouping of switches or by a master ignition switch control. A "T" arrangement or split rocker switches are possible configurations. A master ignition control, if utilized, would need to be carefully evaluated if rotorcraft performance credit is given for engine isolation.
(2) Each group of ignition switches and the master ignition control should have a means to prevent inadvertent operation. "Guarded" switches are the usual means of showing compliance.
565. § 29.1147 MIXTURE CONTROLS.
a. Explanation. This section addresses the arrangement of fuel mixture controls, if installed. Major manual adjustment of the fuel mixture to optimize performance is not normally allowed due to the possibility of engine failure or detonation if significant misadjustment occurs. If "best-power" with respect to fuel mixture is desired, normal practice is to utilize engines with automatic mixture controls, in which case the lever in the cockpit reverts to merely an engine shutdown device. In any case, manual adjustment of the mixture, except for intentional shutdown, should not be prescribed without positive means of ascertaining that the resulting fuel-air mixture is within the range associated with safe engine operation. Some manual mixture adjustment may be acceptable for more efficient engine operation if suitable stops or automatic means are provided to prevent inadvertent engine shutdown with mixture movement or engine malfunction with flight condition changes.
(1) Section 29.1147(a) requires (if mixture controls exist) that controls be arranged to allow:
(i) Separate control of each engine.
(ii) Simultaneous control of all engines.
(2) Section 29.1147(b) requires that each intermediate position of the mixture controls corresponding to a normal operating setting be identifiable by both feel and sight.
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b. Procedures.
(1) Certification data submitted by the applicant should be reviewed to ensure that the design features stated in § 29.1147 exist.
(2) Proper mixture control functioning (to verify the design features of § 29.1147) should be verified as part of the TIA for the certification project.
(3) Compliance is typically shown by use of a side-by-side arrangement of the controls, provided that the arrangement is compatible with other controls and considering that crew attention to the primary flight controls may be a full-time, "hands-on" operation.
566. § 29.1151 ROTOR BRAKE CONTROLS.
a. Explanation.
(1) Paragraph (a) of § 29.1151 is intended to require design features which, for all practicable purposes, prevent brake application in flight even under conditions of reasonably expected crew error or confusion.
(2) Paragraph (b) of § 29.1151 would require warning devices to alert the crew if the brake has not been completely released.
b. Background. Inadvertent or undetected application of the rotor brake is expected to result in excessive heat and fire in the rotor brake area. Rotor brake components are usually located integral with, or in close proximity to, rotor drive system components and, in many cases, close to critical hydraulic main rotor control system components. Fires in these areas would be extremely hazardous.
c. Methods of Compliance.
(1) For Paragraph (a) literal compliance can be achieved by lock-out devices sensitive to the higher RPM. ranges of the main rotor or other flight parameters, hydraulic bypass or lockout devices controlled by flyweight governor systems, etc. The guard required by § 29.921 does not, in itself, provide compliance with this requirement.
For some designs, if careful evaluation of the overall control, including location, guard mechanism, control manipulation requirements, accessibility, etc., provides an extremely high degree of assurance that inadvertent application will not occur, compliance may be assumed. Also, if brake application does occur, annunciation appears, and no immediate hazard to flight operation exists, compliance may be assumed.
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(2) Warning devices supplied to comply with this rule should provide a signal at any time the rotor brake is engaged, including partial engagement. Typically, micro-switches installed to close a circuit to a cockpit warning (red) light when the brake puck moves out of the retract position will provide compliance, provided the designer gives full consideration to the vibration, temperature, moisture, and other environmental considerations appropriate to configuration. Other methods such as system pressure switches, brake handle position indicators, etc., may not provide the warning required by this rule.
567. $29.1157 CARBURETOR AIR TEMPERATURE CONTROLS.
a. Explanation.
(1) This section addresses the air temperature control for carburetor equipped reciprocating engines.
(2) For rotorcraft which have more than one such engine installed, a separate carburetor air temperature control must be provided for each engine.
b. Procedure.
(1) The engine air induction system should incorporate a means for the prevention and elimination of ice accumulations by preheating the air prior to its entry into the carburetor.
(2) Manually operated push/pull systems have been used which operate a flapper valve inside the air induction system. One such system for each engine is one method of compliance.
568. § 29.1159 SUPERCHARGER CONTROLS.
a. Explanation.
(1) This section addresses the accessibility to supercharger controls in the cockpit, if installed.
(2) These controis must be located so they are easily reached by the pilots or, if the rotorcraft is so configured, by a flight engineer.
b. Procedure.
(1) The location and shape of the controls should be conveniently accessible and sufficiently unique to preclude inadvertent actuation of the wrong control.
(2) Compliance is typically shown by a cockpit evaluation.
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569. § 29.1163 (Amenament 29-26) POWERPLANT ACCESSORIES.
a. Explanation.
(1) This section addresses the interface requirements for powerplant accessories which are mounted on the engine or rotor drive system components.
(2) Areas which should be addressed include structural loads imposed upon the engine case and isolation between the accessory and engine oil systems. Electrical equipment isolation from flammable fluids or vapors should be addressed as well as the effect of an accessory failure on the continued operation of the engine and drive system components.
b. Procedures.
(1) Accessories installed and certified by the engine manufacturer can be mounted on the engine without additional justification.
(2) Any accessory to be mounted on the engine, which was not certificated with the engine and does not meet the engine installation design manual requirements, should have a structural analysis showing the mounting of that accessory on the engine will not induce loads into the engine case which are higher than the original design loads.
(3) When the accessory is mounted and operating on the engine, it should not be possible to contaminate either the engine or accessory oil systems. This contamination can take the form of debris following a failure, airborne dirt or water, or any other substance that would impair proper operation of the engine or accessory.
Compliance with these requirements can be accomplished by a combination of test and analysis. The design interface should be such that when the equipment is operating, there are no high/low pressure differentials between the components which would induce fluid transfer between components resulting in a low fluid level in one component and an overfill condition in the other component. Where this potential exists, an analysis and/or test should be used to demonstrate compliance.
(4) Engine mounted accessories which are subject to arcing and sparking must be isolated from all flammable fluids or vapors to minimize the probability of fire. This can be accomplished by isolating the electrical equipment from the flammable fumes or vapors or by isolating the flammable fumes or vapors from the potential ignition source.
Compliance can be shown by analysis.
(5) A failure mode and effect analysis should be submitted which shows that a failure of any engine mounted and driven accessory will not interfere with the continued operation of the engine. If a hazard is created by the continued rotation of an engine 880 Par 569