(ii) Detector units should be of rugged construction, to resist maintenance handling, exposure to fuel, oil, dirt, water, cleaning agent, extreme temperatures, vibration, salt air, fungus, and altitude. Also, they should be light in weight, small, and compact, and readily adaptable to desired positions of mounting.
(iii) The detector system should operate on the rotorcraft electric system without inverters. The circuit should require minimum current unless indicating a fire or unless a monitoring system is in use.
(iv) Fixed temperature fire detectors should preferably be set at 100° F
(37.7° C) to 150° F (65.6° C) above maximum safe ambient temperature, or higher when in compartments where extremely high rate of rise is normally encountered.
(v) Detector system components located within fire zones should be fire resistant.
(vi) Each detector system should actuate a light which indicates the location of the fire. If fire warning lights are used, they must be in the pilot’s normal field of view.
(vii) Two or more engines should not be dependent upon any one detector circuit. The installation of common zone detection equipment prevents the detection system from distinguishing between the engine installations, necessitating shutting down more than one engine.
(6) The sensing portion of the fire detection system should not extend outside of the coverage area into another fire zone. Detectors, with the exception of radiation– sensing detectors, should be located at points where the ventilation air leaves compartments. If a reverse- flow cooling system is used, detectors should be installed at locations which are outlets under both flight and ground operating conditions. Stagnant air spaces should be avoided and the number of ventilation air exits should be kept to a minimum. The ventilation requirements of § 29.1187(e) must also be taken into consideration. Compliance with these recommendations allows the effective placement of a minimum amount of detectors, and still ensures prompt detection of fire in those zones. Radiation- sensing detectors should be located such that any flame within the compartment is immediately sensed. This may or may not be where the ventilation air leaves the compartment.
(7) Fire detectors must be installed in designated fire zones, the combustor, turbine and tailpipe sections of turbine installations.
(i) Engine Power Section (Combustor, Turbine and Tailpipe): This zone is usually characterized by predictable hazard areas which facilitate proper detector location. It is recommended that coverage be provided for any ventilating air outlet as well as intermediate stations where leaking combustibles may be expected.
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(ii) Compressor Compartment: This is usually a zone of relatively low air flow velocities, but wide geographical possibility for fires. When fire detectors other than radiation-sensing detectors are used, detection at air outlets provides the best protection, and intermediate detector locations are of value only when specific hazards are anticipated.
(iii) Accessory Bullet Nose: Where such a compartment is so equipped that it is a possible fire zone, its narrow confines permit sufficient coverage with one or more detectors at the outlets.
(iv) Heater Detector Location: An overheat detector should be placed in the hot air duct downstream of the heater. If the heater fuel system or exhaust system configuration is such that it is a fire hazard, the compartment surrounding the heater should also be examined as a possible fire zone.
(v) Auxiliary Power Unit Detector Location: The use of a combustion-driven auxiliary power unit creates another set of typical engine compartments defined and treated as above. Some units are so shrouded with fireproof material that these compartments exist only within the confines of the shroud. They are still, however, fire zones and must have a detection system.
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CHAPTER 2. PART 29
AIRWORTHINESS STANDARDS
TRANSPORT CATEGORY ROTORCRAFT
SUBPART F - EQUIPMENT
EQUIPMENT - GENERAL AC 29.1301. § 29.1301 FUNCTION AND INSTALLATION.
a. . It should be emphasized that this rule applies to each item of installed Explanation equipment which includes optional equipment as well as required equipment.
b. Procedures .
(1) Information regarding installation limitations and proper functioning is normally available from the equipment manufacturers in their installation and operations manuals. In addition, some other paragraphs in this AC include criteria for evaluating proper functioning of particular systems. (An example is paragraph AC 29 MG 1 for avionic equipment.)
(2) This general rule is quite specific in that it applies to each item of installed equipment. It should be emphasized, however, that even though a general rule is relevant, a rule that gives specific functional requirements for a particular system will prevail over a general rule. Therefore, if a rule exists that defines specific system functioning requirements its provisions should be used to evaluate the acceptability of the installed system and not the provisions of this general rule. It should also be understood that an interpretation of a general rule should not be used to lessen or increase the requirements of a specific rule. Section 29.1309 is another example of a general rule, and this discussion is appropriate when applying its provisions.
AC 29.1303. § 29.1303 (Amendment 29-24) FLIGHT AND NAVIGATION INSTRUMENTS.
a. Explanation. This rule lists the flight and navigation instruments that are required for VFR certification. Several additional rules to be consulted when determining the flight and navigation instrument installation design are § 29.1321, Arrangement and visibility; § 29.1331, Instruments using a power supply; and § 29.1333, Instrument systems. Additional information regarding the different instruments can be found in the Technical Standard Order (TSO) for each one. Compliance with the TSO requirements does not ensure compliance with the appropriate part 29 installation requirements.
Other considerations may also be found by reviewing the requirements of §§ 29.1323,
29.1327, 29.1335, 29.1381, 29.1543, 29.1545, and 29.1547, and Appendix B to part 29.
Paragraphs VIII.(a) and (b) of Appendix B to part 29 include IFR operation considerations for flight and navigation instruments. In addition, if the maximum allowable airspeed is dependent on conditions such as weight and altitude, that Page F - 1
AC 29-2C, Chg 7 2/4/2016 information is normally provided on tables, graphs, placards, or other means in the cockpit and in the rotorcraft flight manual.
(1) This guidance is being revise to clarify the requirements for the non-tumbling gyroscopic bank and pitch indicator required by § 29.1303(f) relative to the specified requirements in § 29.1303(g)(1). A review of § 29.1303 preamble material revealed that the intent of the regulation was to adopt similar levels of safety to transport category rotorcraft as that found in transport category airplanes. Therefore, the requirements of § 29.1303 for transport category rotorcraft are similar to those in § 25.1303 for transport category airplanes, with the exception that transport airplanes require a usable range of 360º in pitch and roll.
(2) For rotorcraft, loss of or misleading primary flight information (attitude, altitude, and airspeed) is considered a catastrophic failure condition in instrument meteorological conditions. For an attitude instrument to be usable, it must be capable of providing the pilot with reliable references to pitch and roll attitudes throughout the instrument’s operating range so a pilot can correctly recognize the extent of the unusual or extreme attitude and initiate an appropriate recovery maneuver. As indicated previously, a TSO approval does not ensure compliance with the part 29 installation requirements, including those requirements in § 29.1303(g)(1).
(i) The minimum usability requirements for the aircraft attitude systems is defined in § 29.1303(g)(1). The phrase in § 29.1303(g)(1) “…is usable through +/- 80 degrees of pitch and +/- 120 degrees of roll" means that the pilot must be able to quickly and accurately determine the aircraft’s pitch attitudes up to 80 degrees nose up and 80 degrees nose down. The ADI must also allow the pilot to quickly and accurately determine the aircraft’s roll attitude to 120 degrees of left and right roll.
(ii) The minimum usability requirement for the aircraft attitude system defined in § 29.1303(g)(1) applies to all attitude systems installed in the aircraft. Attitude systems that do not meet the minimum usability requirements can provide misleading information to the pilot.
(3) Operational rules require equipment with specific operational capabilities (for example, 14 CFR 91.205(d), 135.159(2), and 135.159(3)). Therefore, it is advisable to check the operational rules for the type of operation being considered to ensure the attitude indicator meets the requirements for that operation.
b. Procedures.
(1) The following instruments are flight instruments:
(i) Airspeed indicator.
(ii) Sensitive altimeter.
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(iii) Free-air temperature indicator.
(iv) Non-tumbling gyroscopic bank and pitch indicator.
(v) Gyroscopic rate-of-turn indicator with an integral slip-skid indicator.
(vi) Rate-of-climb (vertical speed) indicator.
(2) The remaining instruments are navigation instruments.
(3) If a speed warning device is required to be included as part of the rotorcraft design, it must meet the performance requirements given in the rule. In addition, the evaluation of the acceptability of the aural warning (i.e., this warning differs distinctively from aural warnings used for other purposes) should be accomplished by flight test personnel as part of their overall cockpit evaluation.
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AC 29.1305. § 29.1305 (Amendment 29-10) POWERPLANT INSTRUMENTS.
a. Explanation. This section specifies those instruments which are required for reciprocating and turbine engine installations. It also provides instrumentation requirements for operating rotorcraft in Category A or Category B. These instruments will provide the pilot with essential data to determine operational status of critical components and select desired performance conditions.
b. FAR 29.1305(a)(4), (a)(6), and (a)(9) requires a warning device for low fuel, gearbox oil pressure, and transmission oil temperature. An indicator/gage is not acceptable for use as a warning device since the indicator/gage is not a primary instrument and therefore is not actively monitored.
c. There are advanced display systems that take advantage of microprocessor power by integrating the processing of several parameters. These systems have to date been referred to as Engine Caution Advisory Systems (ECAS) or as Integrated Instrument Display Systems (IIDS) and possibly other variations of these names. These systems typically integrate propulsion instruments, fuel quantity indication, and caution and warning system into a single display system. In traditional designs the powerplant instruments, fuel quantity display, and the caution and warning system are independent from each other. The integration of these systems/indicators eliminates their independence from one another and increases the probability of loss of more than one indicator/system as a result of a single fault or malfunction. Redundant design is generally applied to compensate for the loss of independence.
(1) This integration and resultant mitigation of independence can result in an increased opportunity for common mode failures. Approval of the compensating features is elevated in importance as it is this aspect that allows the concept to be acceptable and subsequently certifiable. The loss of all displayed information or erroneous information should be considered for determination of worst case criticality.
With this determination of criticality, the design can be evaluated to see that it meets the [Section AC 29.1305 continued on next page] Page F - 7
minimum associated level of design assurance. Additionally, due to space limitations, some systems employ “page over” features that may have some difficulty displaying the required information when needed and human factors aspects must be considered.
(2) The instrument display system must be investigated and found to be acceptable under both normal and emergency conditions, must perform its intended function under foreseeable operating conditions, and must be designed to minimize the hazards in the event of probable malfunction or failure.
(3) It must be shown that there is appropriate redundancy to provide adequate compensation for the loss of independence in the system. If a multi-page system is employed, it must be shown that needed information is displayed when required.
Specific issues that must be addressed to assure compliance with the minimum safety standards are as follows:
(i) The level of most severe hazard must be determined.
(ii) Equivalent reliability and software design assurance to the determined criticality level must be shown.
(iii) Pretest capability must be provided for the warning and caution system to preclude an associated latent failure.
(iv)Human Factors (reference §§ 29.1321 and 29.1322).
d. Additional rules to be consulted when determining the powerplant instrument installation design are §§ 29.1321, Arrangement and visibility; 29.1337, Powerplant instruments; 29.1381, Instrument lights; 29.1543, Instrument markings: General;
29.1549, Powerplant instruments; 29.1551, Oil quantity indicator; and 29.1553, Fuel quantity indicator.
AC 29.1305A. § 29.1305 (Amendment 29-26) POWERPLANT INSTRUMENTS.
a. Explanation. Amendment 29-26 revises, edits, and adds new powerplant instrument requirements. Section 29.1305(a)(4) was revised to require a low fuel warning device for each tank that can be used to feed an engine. The amendment allows a longer time between warning actuation and fuel exhaustion and requires the low fuel warning device to be independent of the normal fuel quantity indication system.
Section 29.1305(a)(17) was changed to extend its application to all rotorcraft (not just those with turbine engines) and to require an indication to the crew of the degree of filter blockage as it relates to the fuel flow requirements in § 29.955. Section 29.1305(a)(19) was revised to require function indicators only for fuel heaters that can be selected or are controllable. A new paragraph (a)(20) was added to § 29.1305 that combined identical requirements for fuel pressure indicators in paragraphs (b)(2) and (c)(2) and modified the applicability of these requirements to only Page F - 8
those fuel systems with devices or components that could adversely affect fuel pressure at the engine, if they fail. It also eliminates the requirement for fuel pressure indicators in fuel systems, such as suction or gravity feed systems, which do not incorporate pumps or filters. A new § 29.1305(a)(21) was added that requires a warning device to indicate to the flight crew the failure of any fuel pump that is required to supply adequate fuel flow to the engine according to § 29.955; such indication is not required for fuel pumps which are demonstrated to be only necessary for engine starting.
Section 29.1305(a)(22) adds a requirement for a warning or caution device to alert the flight crew when particles are detected by the chip detector required by § 29.1337(d). A new § 29.1305(a)(23) added a requirement for powerplant instruments or warning devices for auxiliary power units installed in rotorcraft.
b. Procedures. The requirement and purpose for each instrument is self-explanatory in the amendment. Other sections that should be considered when designing powerplant instruments are listed in paragraph AC 29.1305.
AC 29.1305B. 29.1305 (Amendment 29-34) POWERPLANT INSTRUMENTS.
a. Explanation. Amendment 29- 34 added §§ 29.1305(a)(24) and 29.1305(a)(25) to provide for 30-second/2-minute OEI power ratings.
(1) Section 29.1305(a)(24) adds the requirement that a device or means be provided to alert the crew of the use of the 30-second and 2-minute OEI power level.
The crew should be alerted when the 30-second or 2-minute interval begins and when the time interval ends. The amount of time spent at the 30- second or 2-minute OEI power levels is at the crew’s discretion, unlike the other limits for 30-second OEI that are set by an automatic control required by § 29.1143. The purpose for providing the time interval alerts and automatically controlling the 30-second OEI limits is to free the crew from monitoring the engine instruments during critical phases of flight caused by the loss of an engine.
(2) Section 29.1305(a)(25) adds the requirement for a device to record the usage and the amount of time spent at the 30-second OEI power level and the amount of time spent at the 2-minute OEI power level. The information recorded by this dev ice is for the use of the ground crew to determine if maintenance actions/inspections are to be conducted.
b. Procedures. For the purpose of complying with FAR 29.1305(a)(24) and
29.1305(a)(25), the 2-minute OEI power level is considered to be achieved whenever one or more of the operating limitations applicable to the next lower OEI power rating are exceeded. The 30 -second OEI power level is considered to be achieved whenever one or more of the operating limitations applicable to the 2-minute OEI power rating are exceeded.
(1) A review of the method to meet the requirements of § 29.1305(a)(24) should be conducted by flight test personnel. A determination should be made as to whether Page F - 9
the method used to alert the crew of 30-second or 2-minute OEI power usage can be recognized and understood by the crew.
(2) To meet the requirements of Section 29.1305(a)(25), a device should be installed on the engine or the airframe to record the time and each usage of 30-second and 2-minute OEI power levels. The information on the time and usage of 30- second and 2-minute OEI power should be recoverable from the recording device by ground personnel. The device should not be capable of being reset in flight and should only be capable of being reset by ground personnel. Prior to each flight this device should be capable of being checked for proper operation and to determine if 30-second or 2-minute OEI power levels were used during the previous flight.
c. Integrated Display Systems. This advisory material is to provide guidance for compliance to Part 27 and Part 29 regulations as they apply to integrated display systems. The integration aspects of these systems require some additional issues to be addressed during certification. The term “must” in this advisory material is used in the sense of ensuring the applicability of these particular methods of compliance when the acceptable means of compliance described herein is used. This advisory material establishes an acceptable means, but not the only means of certifying an integrated display system.
(1) Definitions.
(i) Integrity. The term “integrity” for the purpose of this advisory material includes the hardware quality requirements, including reliability; as well as the software level requirements, as defined in DO178B.
(ii) Criticality. The term “criticality” refers to the five levels of criticality addressed in FAA Advisory Circulars AC 27-1B and AC 29-2C.
(2) Related documents.
(i) Federal Aviation Regulations (FARs) paragraphs 21.21, 29.1301,
29.1309, 29.1305, and 29.1322
(ii) Standards - Latest revision of RTCA/DO178 and RTCA/DO-160; SAE documents
(iii) ARP4754 and ARP4761
(3) Background. A tendency to integrate functions/indications that have previously been independent is a result of technology advancement. Microprocessor driven systems have facilitated the ease of this integration. Integrated Instrument Display System (IIDS) or Engine Instrument and Caution Advisory System (EICAS) are examples of integrated display systems. IIDS, EICAS, or any other similar systems are defined as a combination of engine instruments ( previously independent indicators), Page F - 10