multiengine configuration, the faulty alternator/generator should be removed without affecting operation of the remainder of the system.
(ili) The annunciation circuitry should be checked for indication of failures such as overvoltage, tripped generators, overcurrent, open feeders, open tie breakers, etc.
(6) Aircraft Ground Tests. If the above tests (reference b(1) through (4) inclusive) are conducted on a bench setup, enough tests should be repeated on the aircraft to validate the bench test results. The following tests should be conducted on the aircraft:
Normal Battery Starts. Start all engines on the aircraft following the normal procedure prescribed in the flight manual. Record starter volts and amperes, time, and any other parameters deemed necessary.
Ground Power Cart Starts. If the aircraft is equipped with a plug for a ground power cart, use the procedure described in the flight manual and start all engines. Record starter volts and amperes, time, and any other parameters deemed necessary.
Emergency Battery Operation (if provided). The emergency battery mode of operation should be tested to assure at least proper switching, annunciation, and battery capacity. In some instances, an analysis of battery capacity may be adequate.
(iv) Other Tests. Conduct other tests as necessary to demonstrate proper operation of the specific design being evaluated.
(V) Distribution System Tests. With all systems operating individually, open and close feeder circuit breakers and system circuit breakers and assure separation of power sources for essential systems. For example, removing power from one bus by opening a feeder should not result in loss of both NAV 1 and NAV 2 or both COMM 1 and COMM 2 or both attitude gyros, or for example, opening NAV 1 circuit breaker should not affect NAV 2, etc. If the opening of the feeder protection has been satisfactorily demonstrated on a bench test facility, it should not be necessary to repeat that demonstration on the actual aircraft. The effect of loss of power sources should also be demonstrated on the aircraft. Reference §§ 29.1357 (e) and 29.1309.
(7) Environmental Qualification. Each component of the system, such as relays, switches, alternator, generator, sensor, regulator, diode, etc., should be qualified to the critical environmental parameters. The temperature, altitude, humidity, and vibration expected in the approved aircraft operational envelope should fall within those limits the applicant substantiates for the electrical system components. (Refer to Paragraph 621 of this advisory circular.)
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(8) Electromagnetic Compatibility. At no time during any of the qualification testing described herein should objectionable interference in the aircraft's radio, navigation, cockpit instrument, autopilot, or interphone system be considered acceptable.
NOTE: The quantitative type testing used for Items (7) and (8) above is outside the scope of this document. The latest revision of RTCA Document DO-160 is an acceptable standard.
(9) Transient Tests. The D.C. system should be tested and shown to exhibit surge, ripple, and spike voltages within the limits of the latest revision of RTCA Document DO-160.
The surge and ripple voltage tolerance of avionic equipment is defined by the latest revision of RTCA Document DO-160. Category Z is considered applicable to rotorcraft D.C. systems.
The voltage spike tolerance of avionic equipment is defined by the latest revision of RTCA Document DO-160.
(10) Ground and Bench Test Report. At the conclusion of the ground and bench test program a report should be prepared and submitted that contains at least the following:
System schematic (including instrumentation tie-in).
(iT) Instrumentation list (including calibration records).
Test result recordings.
(iv) Detailed procedures and results obtained.
(v) Conformity inspection records.
(vi) Other data, photographs, etc., to describe the test setup.
(vii) Summary of the test results. This summary should show the maximum load to which each bus, alternator/generator, etc., has been tested.
(vili) Analysis of test results. This should describe how compliance with the regulations has been shown. It should include consideration of the critical failure modes. Refer to Paragraphs 776a(4) (ii) and 621c of this advisory circular for further information on failure analyses.
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c. Flight Test Procedures.
(1) Alternator/generator cooling tests should be conducted in accordance with Paragraph 778 of this advisory circular.
(2) On multiengine rotorcraft, single-engine air starts should be conducted using the manufacturer's recommended procedures. This should be accomplished for each engine individually.
(3) A cockpit evaluation of the electrical system should be conducted to evaluate:
(i) Switch, circuit breaker, and annunciator identification.
(її) Visibility of placarding, switches, etc., during bright sunlight and night operation.
Color of annunciators as related to the function/malfunction annunciated.
(iv) Load meter readability.
(v) Access to essential switches, circuit breakers, etc.
(vi) Electromagnetic interference.
(vil) Compatibility of the electrical system with the rotorcraft flight manual and the need for additional procedures in the RFM.
(vili) Clarity of functions such as opened feeder breakers, tie breakers, related annunciation, and necessary corrective action in the event of malfunction.
(ix) Absence of undesired functions in relation to switch combinations.
778. STANDARDIZED TEST PROCEDURE FOR ROTORCRAFT GENERATOR COOLING.
a. Lest Requirements.
(1) General. The applicant should contact the generator (alternator) manufacturer and obtain the maximum limits for the unit to be tested. This will normally be in terms of temperatures at various locations within the unit (stator, bearings, diodes, heat sinks, brushes, etc.) or in terms of pressure drop across the generator. The manufacturer should either supply an instrumented unit or give complete details for instrumenting the test unit.
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(2) Instrumentation.
Load Bank. A load bank will usually be necessary to load the test unit to the amperage limit for which approval is requested.
(Il) Ammeter. An ammeter should be provided with sufficient resolution to assure the amperage load is being maintained at the desired level.
(Il) Temperature/Pressure Readouts. Readouts which are compatible with the temperature or pressure sensors installed in the test unit should be provided.
(iv) Calibration Records. Calibration records should be available for all instrumentation.
(v) Recordings. Permanent recordings should be provided for time, temperatures, current and/or pressure. The recording device should have provisions for placing event marks on the recording medium.
(3) Regulatory References. Sections 29.1301, 29.1309, 29.1351, 29.1363(b),
29.1521(e), 29.1041, 29.1043, 29.1045, 29.1047, and 29.1049.
(4) Miscellaneous. The results obtained from the tests should be corrected for hot day conditions using a standard lapse rate (3.6° F/1,000 feet).
b. Test Procedures.
(1) Single Engine Procedure.
(i) The cooling test is to be conducted during ground operation and climb-out, cruise and approach flight regimes.
All ground operational and in-ground effect hover tests should be conducted in ambient winds of 5 knots or less. Wind direction relative to the aircraft should be from the most critical direction.
(ili) The battery may be connected to the bus during the generator/alternator cooling test. The generator/alternator temperatures should be recorded at intervals sufficiently close to show the rate of temperature increase and stabilization. The temperature may be considered stabilized when it peaks and has not increased in the last 5 minutes. The climb-out speed and power setting should correspond to the best rate of climb speed, using maximum continuous power or any other normal conditions of climb that would cause the generator/alternator temperatures to be critical. The cruise test should be conducted at maximum altitude in the cruise configuration. Generator/alternator cooling should be conducted at rated output Par 778 1215
consistent with the RPM at which it is operating. For instance, during the ground tests the engine RPM may be lower than that necessary to sustain maximum rated amperage output. In this case the maximum amperage output of the generator/alternator corresponding to the lower RPM should be assured.
(iv) The test sequence should begin with about 30 minutes of ground operation to account for taxi and holding times, and end 5 minutes after all temperatures have peaked after engine shut down.
(2) Multi-engine Procedures. Conduct a generator cooling test in accordance with the following procedure:
(i) All ground operational and in-ground effect hover tests should be conducted in ambient winds of 5 knots or less. Wind direction relative to the aircraft should be from the most critical direction.
(ii) After engine start, load the instrumented generator to its proposed amperage limit and begin recording temperatures.
(iii) A total of 30 minutes should be spent on the ground prior to takeoff.
This is to account for taxi and holding times.
(iv) After takeoff, climb at single-engine best-rate-of-climb speed using maximum continuous power, to the single-engine service ceiling. Above this, continue at twin-engine best-rate-of-climb speed, using maximum continuous power on both engines, to maximum altitude.
(V) Cruise at maximum altitude until all generator temperatures stabilize.
Temperatures shall be considered stabilized when they have peaked and have not increased for a period of 5 minutes.
(vi) Descend, conduct an approach to include a go-around, hover until temperature stabilizes, then land and continue to record temperatures after shut-down until 5 minutes after all temperatures have peaked.
(vii) Conduct cooling tests with the rotorcraft hovering at both the minimum and maximum hover altitudes.
(vill) Correct all results for hot day conditions. Use the standard lapse rate of 3.6° F/1,000 feet for consideration of altitude. See Paragraph 621 of this advisory circular for details on temperature correction.
(ix) If at any time during the testing it appears the manufacturer's limits are to be exceeded, the amperage load on the test generator/alternator should be reduced to prevent this from happening.
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779. Sections 29.1301, 29.1309, and 29.1322 ANNUNCIATOR PANELS.
a. Explanation.
(1) The annunciator panel design should be reviewed for the presence of failure modes that can cause illumination of multiple panel segments.
(2) Many test circuits that are diode isolated are vulnerable to this condition. A typical sequence begins with the shorting of a test circuit diode. This failure is undetectable and goes unnoticed until an actual failure condition occurs which causes the associated panel segment to illuminate. At this time all panel segments connected to the test circuit will illuminate.
(3) This configuration becomes a special problem when one or more of the panel segments are red. A red light calls for immediate action by the crew, and the crew does not have adequate information for immediate action when many false panel segments are illuminated.
(4) If the design review indicates a problem, a redesign of the panel to eliminate the condition is considered to be the best solution and is highly encouraged.
b. Procedures.
(1) An alternative to panel redesign might be the following:
(i) Review the annunciator panel design and note which segments are red.
(її) Determine if cross reference information is available in the cockpit to allow elimination from consideration of any the red segments. (Example: Red low fuel pressure light and low fuel pressure gauge. Normal operation of the gauge would be a reason to assume the light did not cause the problem.)
(iii) Where a cross reference is available, further design review of that function is not necessary; however, it may be appropriate to include procedural information in the emergency procedures section of the rotorcraft flight manual.
(iv) If cross references are not available for red segments, additional isolation should be incorporated into the annunciator design for those functions.
(2) If cross referencing is not practical the following approach is encouraged.
(i) Review the annunciator panel design and note which segments are red.
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Determine if isolation diodes are checked during the application of battery or external power before starting the engines. (Example: Red low oil pressure light. If isolation diode is shorted, all panel segments will light as soon as battery or external power is applied.)
(iii) When the isolation diode can be checked before starting engines, further design review is not necessary.
(iv) If diodes are not automatically checked before starting, then additional isolation, should be considered.
c. Annunciator Panel Arrangement. The annunciator panels should be arranged in a logical manner to reduce the crew's time required to locate faults and to increase their efficiency in following Aircraft Flight Manual procedures. For example, engine annunciators on multiengine rotorcraft should be physically located on the panel to coincide with engine location (left or right) so that properly operating engines are not inadvertently shut down due to crew confusion over which engine has malfunctioned.
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780. RESERVED.
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781. Sections 29.1541, 29.1543, and 29.1549 (Amendment 29-12) INSTRUMENT MARKINGS.
a. Background and Explanation.
(1) Aircraft instruments have historically been marked in a variety of ways and with an interesting assortment of symbols. During this period, a limited number of regulatory requirements have been incorporated in the FAR 29, Subpart G, "Markings and Placards," and these efforts have standardized some basic aspects of instrument marking for rotorcraft. As rotorcraft have become increasingly complex with increased number of engines, one-engine inoperative ratings, more sophisticated instrumentation, etc., the need for more specific standards has greatly increased.
(2) It is vitally important that instrument markings be standardized among rotorcraft. When markings are not standardized, considerable confusion and additional workload may be introduced into the cockpit environment. If markings are not standard, it is conceivable that a marking in one rotorcraft could mean the opposite of a similar marking in another rotorcraft. The results of such a situation could be disastrous when pilots fly several rotorcraft models, and particularly in transport rotorcraft under 12,500 pounds, which do not require a pilot type rating.
(3) The following guidance is offered for the purpose of obtaining a general standardization of instrument markings. It is realized that there are a great many variations in instrument presentations for which all guidance may not apply. This is particularly true of new designs, such as cathode ray tube (CRT) displays currently being presented. It is of overriding importance that the philosophies included here be administered, even if specific guidance cannot be applied for particular designs.
Instrument markings are provided to aid interpretation of instruments quickly and accurately. Good instrument markings should indicate operating conditions at a glance.
The best markings are ordinarily the simplest markings.
b. Procedures.
(1) Limits. Each maximum allowable limit substantiated for safe operation must be marked with a red line. This marking should be a red radial line for circular gages. If there is a minimum allowable limit for safe operation, this value should also be marked with a red (radial) line. The use of multiple red (radial) lines should be avoided except where their use is readily usable by the pilot. Normally, no more than one maximum and one minimum red radial line should be incorporated on any one instrument to minimize confusion and avoid potential aircrew errors; however, use of multiple red radial lines may be permitted if such marking can be presented in an acceptable manner.
(2) Normal Operating Range. Each normal operating range should be marked with a green arc or green line which does not extend beyond the maximum and 1220 Par 781
minimum values for continuous safe operation. Discontinuities in width have been used when normal ranges vary with other parameters. Integrating instruments in place of these markings should be encouraged although there may be no regulatory requirement for them.
(3) Cautionary Ranges. Time limited ranges, precautionary ranges, or ranges for which special operating procedures are required should be marked with a yellow arc or yellow line. If a yellow range is used to indicate a special operating procedure, information describing the special procedure should be included in the Rotorcraft Flight Manual.
(4) One-Engine-Inoperative Markings. One-engine-inoperative (OEI) ratings represent a special challenge for retaining simplicity and clarity in powerplant instrument markings. OE ratings are eligible to be used only during an extremely small portion of total flight time; therefore, they should not dominate the presentation or obscure other markings. They are needed only for reference. Indices for 2½-minute and 30-minute power may be marked above the takeoff power redline on engine power instruments. OE reference markings should be clearly distinct from the normal all-engines operating markings. One acceptable means of marking OEl limits has been narrow dashed radials with yellow for 30-minute, and red for 2½-minute limits. OEI markings should be consistent between gages. For example, a 30-minute marking on an N1 or torque gage should be similar in appearance to the 30-minute marking on the engine temperature gage.
(5) Red Arcs or Ranges. Sections 29.1549(d) and 29.1553 allow the use of red arcs. Experience has proven that when red arcs are used to indicate maximum or minimum values, the meaning of a red line loses its significance. Therefore, the use of red ranges or arcs to indicate limit values should be discouraged. Red is conventionally used to represent a limit (maximum or minimum) for which an aircraft or component has been substantiated. A "range" of limits for a given parameter is not consistent with the definition of the terms "limit," "minimum," or "maximum." In addition, a red arc tends to imply that more than one value is limiting, that a scale is provided to show operation within a range of values, and that an absolute limit may not exist until the extreme of a red range is attained. These implications must be avoided wherever possible by specifying a single limiting value and marking it with a single red line (radial). If readings in excess of that value were indicated, it would then be obvious to the crew that a limit had been exceeded. A red arc may be used to indicate a transient vibration range as indicated in § 29.1549(d); however, if the range is a cautionary range and not a prohibited range, use of a yellow arc is recommended. The fuel gage configuration described in § 29.1553 is considered a special application of red arcs. Occasionally a red arc has been utilized when limits vary with other parameters. Discontinuities in width could conceivably represent limits when other parameters are considered. The use of integrating instruments would alleviate much of the problem and should be encouraged although it is recognized that there may be no regulatory requirement for them.
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(6) Elight Evaluation. In evaluating gage markings, the final criterion must be, "Are the markings adequate for correct interpretation by the crew?" FAAJAUTHORITY evaluations of gage markings should begin early in a certification program utilizing a cockpit or aircraft mock-up whenever possible. All required gages and gage markings must be readable from each pilot station. Depending on cockpit and window geometry, gages should be evaluated in direct sunlight unless they are located high on the panel underneath a substantial glare shield. Evaluation in direct sunlight is especially important for any displays using light bars of digital lighting segments, such as digital radar altimeter presentations or vertical scale instruments using light segments.
Required gages must be readable without upper body movement or extensive head movement by the crew. Evaluators should be especially alert to any scale markings or range markings which are obscured by parallax, as such features are unacceptable. If the aircraft is to be approved for night operation, each required indicator must also be evaluated during night lighting conditions. The same visibility requirements apply for night; however, the evaluator should particularly look for lighting features which may change or obscure the colored markings. For example, in one case, red gage markings were totally obscured by red instrument lighting. Except for minor changes, lighting should be evaluated in flight in order to correctly evaluate vibration effects and various background lighting conditions.
(7) Digital Instruments.
For purposes of this discussion, two types of digital indicator are considered: (1) an indicator which consists of a column of light segments which illuminate sequentially to display changing values, and (2) an indicator which consists of horizontal and vertical line segments in the configuration of a block "g" to display numerical values. Both indicator types work well for parameters where trend information is generally not needed such as engine oil pressure or temperature.
However, for rapidly changing parameters such as engine exhaust gas temperature, torque, or RPM, trend information may not be attainable. Advisory Circular 20-88 (guidelines on the marking of power plant instruments) specifies that instrument markings are intended to provide necessary information at a glance. Trend information for power indicators is vitally important for safe operation of a rotorcraft, and this information must be obtainable at a glance. For the columnar light segments, the ability to quickly detect trend information is largely a function of the resolution provided by single segments (e.g.; if there are two segments for each percent RPM, the ability to detect trend information is better than if there is only one segment for each percent RPM). For digital indicators displaying numerical values, trend information may be unattainable because rapidly changing parameters produce a blur, and this design may be unsuitable as a single source of information. The evaluator should use a great deal of caution to assure adequate trend information is available in primary power and rotor indicators of digital design.
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7/30/97 АС 29-2B (її) Another area of concern in digital and moving tape instruments is the ability to determine when limits are being approached. Color code markings are frequently incorporated on the moving face of a tape or digital presentation. In such cases, it is mandatory that limit markings be affixed adjacent to the presentation, or that another means be provided so that the pilot can anticipate approaching a limit. The beginning and end of normal and cautionary ranges should be marked adjacent to the display. The entire range need not be color coded adjacent to the display if the colors are integral on the face of the tape or in the individual digital segments. Marking of limit values solely on the tape or in the colored light segments alone is unsatisfactory.
Marking of digital indicators displaying numerical values is adequately addressed in AC 20-88, Paragraph 3, General.
(iii) Appropriate failure modes should be evaluated during the system analysis. This will ordinarily include portions of the digital display. Such failures should be detectable whenever they affect reading accuracy. As a result of this analysis, the system may incorporate a test feature which assures all digital segments operate satisfactorily. This feature should be encouraged.
(8) Additional Markings. To keep markings standardized and uncomplicated, only the FAA/AUTHORITY-approved ranges and limits should be included. Items such as manufacturer's recommended values or manufacturer's warranty information are inappropriate for instrument markings and should not be included. Such information may be presented elsewhere. Transient limits may be indicated by a small red index such as a dot or triangle. Information defining allowable conditions for each transient index should be in the rotorcraft flight manual (e.g., maximum for starting, 12 seconds).
(9) Airspeed Indicator. While the foregoing information is generally applicable to airspeed indicators, some particular features warrant additional attention.
(i> A red cross-hatched radial line should be located at power-off VNE if that value is less than power-on VNE:
Many rotorcraft have erratic, unreliable, or nonrepeatable airspeed indications at low speed which warrant caution when operating in that speed range. In such cases, a yellow arc on the instrument with appropriate flight manual explanation has been found acceptable.
(ill) Indicated airspeed values should be utilized for all airspeed indicator markings.
(iv) Airspeed "bugs" may be used to highlight important takeoff, landing, or limit speeds. This concept may generally be encouraged; however, there are a maximum number of "bugs" that can be utilized without confusion for any given indicator. Typically, two "bugs" are acceptable; three or more are questionable. "Bugs" may also be used on a variety of instruments other than the airspeed indicator.
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