(1) The detector system should be designed for highest reliability to detect a fire and not to give a false alarm. It is desirable that it only responds to a fire and misinterpretation with a lesser hazard should not be possible. Engine overtemperature, harmless exhaust leakage, and bleed air leakage should not be indicated by a fire detector system. A fire detection system should be reserved for a condition requiring immediate measures such as engine shutdown or fire extinguishing. There are three general types of detector-procedure systems that are commonly used:
(i) A manual system utilizes warning lights to alert the pilot who then follows prescribed cockpit procedure as a countermeasure. A manual system is adequate for hazards in which a few seconds are not important.
(ii) There is also a semi-automatic system. Occasionally a rotorcraft becomes so complex that the emergency procedure exceeds reasonable expectations of the pilot. In such cases, psychology should be weighted against complexity, and “panic switches,” combining multiple procedure functions, should be provided to simplify the mental demands on the pilot. Speed is gained by such designs for hazards which may need it.
(iii) The detector of an automatic system automatically triggers the appropriate countermeasures and warns the pilot simultaneously. Such a system should be carefully evaluated to assure that the advantages outweigh the disadvantages and potential malfunctions.
(2) Fires, or dangerous fire conditions can be detected by means of various existing techniques. The following is a partial list of available detectors:
(i) Radiation-sensing detectors.
(ii) Rate-of-temperature-rise detectors.
(iii) Overheat detectors.
(iv) Smoke detectors.
(v) CO detectors.
(vi) Combustible mixture detectors.
(vii) Fibre-optic detectors.
(viii) Ultraviolet.
(ix) Observation of crew or passengers.
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(3) In many rotorcraft it is desirable to have a detection system which incorporates several of these different types of detectors. Radiation- sensing detectors are most useful where the materials present will burn brightly soon after ignition, such as in the powerplant accessory section. Rate of rise detectors are well -suited to compartments of normally low ambient temperatures and low rates of temperature rise where a fire would produce a high temperature differential and rapid temperature rise. It should be noted that under certain circumstances, where a relatively slow temperature increase occurs over a considerable period of time, a fire can occur without detection by rate of rise detectors. Overheat detectors should be used wherever the hazard is evidenced by temperatures exceeding a predicted, set value. Smoke detectors may be suited to low air flow areas where materials may burn slowly, or smolder. Fibre- optic detectors can be used to visually observe the existence of flame or smoke. The three major detector types used for fast detection of fires are the radiation-sensing, rate-of-rise, and overheat detectors. Radiation- sensing detectors are basically “volume” type which senses flame within a visible space. Overheat -fire detectors can be obtained in either “continuous” or “unit” type.
(4) The detector system should:
(i) Indicate fire within 15 seconds after ignition, and show which engine compartment in which the fire is located.
(ii) Remain on for the duration of the fire.
(iii) Indicate when the fire is out.
(iv) Indicate re-ignition of the fire.
(v) Not by itself precipitate or add to the potential of any other hazards.
(vi) Not cause false warnings under any flight or ground operating condition.
A false fire detector indication could significantly increase crew workload, impair crew efficiency, or reduce safety margins and so is classified as a major failure condition. In consequence, such false fire detector indication should be shown to be improbable based on a probability assessment and service experience of the fire detector system.
If the probability of the fire detection system experiencing a false indication cannot be shown to be improbable, a secondary means of determining the validity of the fire indication should be provided.
(5) Additional features of the detection system are as follows:
(i) A means should be incorporated so that operation of the system can be tested from the cockpit.
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(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