550.-560. RESERVED.
Intentionally Left Blank 726 (thru 736) Par 550
SECTION 32. POWERPLANT CONTROLS AND ACCESSORIES
561. §. 27.1141 (Amendment 27-12) POWERPLANT CONTROLS: GENERAL.
a. Explanation.
(1) Section 27.1141(a) references §$ 27.777 and 27.1555. The detailed compliance procedures for powerplant controls arrangement and markings are found in these sections.
(2) Each flexible powerplant control should be approved.
(3) In order to prevent power failure due to improper powerplant control valve positioning, § 27.1141(c) specifies acceptable open/closed positions for manual valves.
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.
(4) 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.
b. Procedures.
(1) Procedures for § 27.1141(a) are contained in detail in §§ 27.777 and
27.1555.
(2) Compliance with § 27.1141(b) may be accomplished by qualifying the control to Mil-C-7958, "Controls, Push-Pull, Flexible, and Rigid," or other approved standards.
(3) Compliance with § 27.1141(c)(1) may be accomplished by installing manual valves which have positive stops in the full 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 Paragraph (c)(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 closed and illuminates while the valve is transitioning.
(4) Compliance with § 27.1141(d) can be accomplished by performing a failure mode and effects analysis (FMEA) to determine that no single failure or malfunction will Par 561 737
cause failure of any powerplant control function necessary for safety. Included in this FMEA should be calculations showing the likelihood of any combination of failures of the powerplant control systems that would cause failure of any powerplant function necessary for safety is improbable. One acceptable procedure for documenting the analysis is contained in Society of Automotive Engineers (SAE) Fault/Failure Analysis Procedure ARP 926A, revised November 15, 1979.
561A. § 27.1141 (Amendment 27-23) POWERPLANT CONTROLS: GENERAL.
a. Explanation. Amendment 27-23 changed § 27.1141(c) to extend its applicability to any powerplant valve regardless of the location of the valve control. The previous rule was only applicable for valves in the cockpit. Valves are excluded if their function is not required for safety.
b. Procedures. This rule change did not change the suggested methods of compliance.
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562. RESERVED.
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563. § 27.1143 (Amendment 27-11) ENGINE CONTROLS.
a. Explanation. This regulation describes the arrangement and operation of the engine controls.
(1) Each throttle mechanism should be independent of the throttles for other engines.
(2) The arrangement of the independent throttles should allow simultaneous control of all engines with one hand.
(3) Immediate actuation at the engine control should be provided by any given input at the throttle control in the cockpit.
(4) If throttle controls incorporate a fuel shut-off feature, a means should be provided to prevent inadvertent movement to the shut-off position. This means should-- Provide a positive lock or stop at the idle position. An idle detent (mechanical or electrical/mechanical such as solenoid) is an accepted arrangement.
(il) Require a separate and distinct operation to place the control in the shut-off position. Separate action (switch or button) to displace the idle stop or distinct offsets in throttle motion to allow movement from the idle stop to shutoff are accepted arrangements.
b. Procedures. None.
563A. § 27.1143 (Amendment 27-23) ENGINE CONTROLS.
a. Explanation. Amendment 27-23 revises § 27.1143 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.
(1) Proper operation of the power control functions should be verified as part of the Type Inspection Authorization (TIA).
(2) Compliance with § 27.1143(d)(1) has been shown successfully in the past by using idle detentes (mechanical or electrical/mechanical, such as a solenoid).
(3) Compliance with § 27.1143(d)(2) has been achieved by using a switch or button to displace the idle stop. Distinct offsets in throttle motion to allow movement from the idle stop to shutoff have also been used to show compliance.
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563B. § 27.1143 (Amendment 27-29) ENGINE CONTROLS.
a. Explanation. Amendment 27-29 introduced the option of using 30-second/2-minute OE power ratings to multiengine rotorcraft. This amendment revises § 27.1143 by adding the requirement for automatic control of 30-second OEI limits in the new Paragraph 27.1143(e). Automatic control of the 30-second OEl limits are required to prevent exceeding the remaining power sections OEl limits 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 exceeding the limit.
b. Procedures. The automatic controls used to prevent 30-second OEl limit exceedances can be installed on the airframe or the engine. The applicant should demonstrate that 30-second OEI limits that can affect the continued operation of the drive system or engine such as gas generator speed, power turbine 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. § 27.1145 (Amendment 27-12) 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.
(2) The objective is to provide a means to quickly shut off all ignition, if required, while at the same time providing protection against inadvertent ignition switch operation.
(3) Section 27.1145(a) does not specifically state that turbine engines which do not require 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 27.1145(a) is self-explanatory in specifying that a means be available to quickly shut off all ignition 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.
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(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. § 27.1147 MIXTURE CONTROLS.
a. Explanation. This section addresses the arrangement of fuel mixture controls for reciprocating engine installations and applies only if mixture controls are installed.
Note that this control, as used in rotorcraft, is an engine shutdown device. Adjustment of the fuel mixture in flight is not allowed to demonstrate Part 27 compliance, but 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.
b. Procedures.
(1) The arrangement should allow--
(i) Separate control of each engine; and
(ii) Simultaneous control of all engines.
(2) Compliance may be accomplished by a side-by-side arrangement of the controls to allow either separate or simultaneous control.
566.-567. RESERVED.
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568. § 27.1151 (Amendment 27-33) ROTOR BRAKE CONTROLS.
a. Explanation.
(1) Amendment 27-33 added a new § 27.1151 that establishes requirements for rotor brake controls. Paragraph (a) is intended to require design features which, for all practicable purposes, prevent inadvertent brake application in flight even under conditions of reasonably expected crew error or confusion.
(2) Paragraph (b) requires warning devices to alert the crew if the brake has not been completely released.
b. Background. Inadvertent or undetected application of the rotor brake may be 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 some cases, close to critical hydraulic main rotor control system components. Fires in these areas would be extremely hazardous.
c. Method of Compliance.
(1) For Paragraph (a), literal compliance can be achieved by lock-out devices sensitive to the higher RPM range of the main rotor or other flight parameters, hydraulic bypass or lock-out devices controlled by flyweight governor systems, or engines control position, etc.
The guard required by FAR 27.921 does not, in itself, provide compliance with this requirement. However, if careful evaluation of the overall control, including location, guard mechanism, control manipulation requirements, accessibility, etc., provides a 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.
(2) Alerting devices supplied to comply with this rule should provide a signal at any time the rotor brake is engaged, including partial engagement. This means to alert the crew could be:
- A warning light indicating the mechanical control position, or the position of the brake for a power assisted system, or
- An unambiguous device warning the crew that the rotor brake is engaged (or partially engaged), or
- A locking device preventing the engine starting when the rotor brake control is not completely released.
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569. § 27.1163 (Amendment 27-23) 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 driven accessory after a failure or malfunction, provisions to stop its rotation or eliminate 746 Par 569
the hazard must be provided. The effectiveness of this device should be demonstrated by test.
(6) The main transmission and rotor drive system should be protected from excessive torque loads and damage imposed upon them by accessory drives. One method which has been used is a torque limiting device; (i.e., shear section of main rotor driveshaft). The effectiveness of any protection device should be demonstrated by test.
570.-583. RESERVED.
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584. RESERVED.
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