(4) For electrical instruments, the power is considered to be adequate when the voltage is within approved limits. The source of power for the visual means of indication must be independent of the source of power for the instrument itself. Independent in this case means a separate circuit protective device and a separate distribution system bus.
(D) Multiple System Separation. Multiple systems performing the same function are required in certain instances because it is probable that a single system will fail. Separation of such systems would preclude a single fault from causing a multiple system failure. The following should be considered:
(1) When possible, cable routing should be accomplished to assure the maximum separation; for example, one system routed on one side of the rotorcraft and the other system on the opposite side. Some areas, such as pedestals, junction boxes, and equipment racks bring systems close together, and in these areas physical separation may be minimal.
(2) Systems that are required to be duplicated should not be routed through one electrical disconnect plug.
(3) System grounds should be evaluated to assure wiring for two required systems are not grounded to the same terminal. If a terminal strip contains grounds for multiple systems, it should be grounded to the rotorcraft's airframe in two places from two separate terminals.
(E) Circuit Protective Devices. All systems that are "required" for IF operation are considered to be necessary for safe IFR operation, and the circuit protective devices for those systems should generally be accessible to the crew in the cockpit so they can be readily reset or replaced in flight. For example, where a capability is provided that is above the minimum certification requirements, accessibility may not be an issue. A tradeoff here, however, is that additional equipment may be required for dispatch in IFR operation.
The location of the generator field protective devices has been a problem in some rotorcraft. The protective devices that can result in the loss of a required power system source should be capable of being reset or replaced in the cockpit while in flight. This position is further supported by the occurrence of nuisance opening of circuit protective devices in rotorcraft. Further discussion on this issue is included in Paragraph 655b(4) of this advisory circular.
(F) Intercommunication System. All audio for the entire rotorcraft comes together at this system. An evaluation should be made to assure that no single failure will result in the loss of all audio for the rotorcraft. Check for common grounds, common connectors, etc. Power inputs should also be disabled.
1188 Par 775
(14) Rotorcraft Flight Manual Material.
In addition to other required information, the limitations section of the Rotorcraft Flight Manual (RFM) or RFM Supplement must include the approved IFR flight envelope, minimum FR crew requirements, the minimum required equipment for dispatch into IF conditions that is not covered by the operating regulations, and the maximum approach gradient which has been approved. If a significant loss of altitude is experienced in any flight regime or maneuver during certification analysis or testing, the emergency operating procedures should include a statement of this altitude loss along with any other appropriate information.
(ii) The limitations section of the RFM should not include restrictions prohibiting external cargo operations. These operations are covered by FAR Parts 91 and 133 and all external load operations conducted under these parts must be approved by the controlling operations inspector. It is the responsibility of the operator to demonstrate and the operations inspector to confirm that any external load operation, including en route IFR, can be safely conducted.
(15) Rotorcraft Flight Below Instrument Flight Minimum Speed.
(i) The advent of steep angle, decelerating precision instrument approach procedures will necessitate flying at airspeeds below the instrument flight minimum speed (VINI) established for most rotorcraft under FAR 29, Appendix B, Paragraph II(c).
(il) Applications for findings of equivalent safety to approve instrument flight below VMINI will be considered for rotorcraft meeting at least the following criteria:
(A) The rotorcraft is certified for IFR flight.
(B) For constant airspeed approach approval: a minimum approach airspeed is specified by the applicant, at which the rotorcraft is demonstrated to be safely controllable and capable of instrument flight without undue pilot effort for the duration of the approach and transition to missed approach, including acceleration to an airspeed above VMINI.
(C) For decelerating approach approval: a two or three cue flight director is provided as required equipment, and the rotorcraft is demonstrated to be safely controllable and capable of instrument flight without undue pilot effort for the duration of the approach and transition to missed approach, including acceleration to an airspeed above VMINI- (D) The rotorcraft is demonstrated to be safely controllable following single failures of aircraft systems not shown to be extremely improbable at the minimum Par 775 1189
approach airspeed specified by the applicant or encountered during a decelerating approach.
(E) The RFMS contains the following information in addition to the requirements of Paragraph IX of Appendix B to FAR 29:
(1) Minimum approach airspeed, if applicable.
(2) Additional aircraft equipment requirements for flight below MINI and/or the minimum approach airspeed, if applicable.
(3) Maximum approach angle.
(4) Maximum allowable surface wind for safe conduct of the approach.
1190 Par 775
Par 775 7/30/97
ACCEPTABLE 20 15 10
UNACCEPTABLE 5 -0.3 -0.2 -0.1 DAMPING RATIO ( S) 0.05 O.1 0.15 AC 29-2B ' FIGURE 775-1. ROTORCRAFT DYNAMIC STABILITY REQUIREMENTS FOR IFR
776. CERTIFICATION PROCEDURE FOR ROTORCRAFT AVIONICS EQUIPMENT.
a. Pre-Test Requirements.
(1) General. This test guideline has been prepared as an aid in the evaluation of rotorcraft avionics (aviation electronics) equipment installations. The criteria presented are not to be considered exclusive, but are offered as one method of evaluating design practice and performance. The testing and qualification of an electronic installation should be considered as consisting of three phases:
preinstallation, ground, and flight. The amount of testing necessary during each phase will vary with the amount of testing performed on previous phases. For example, if a system is TSO'd, the preinstallation performance is probably substantiated and therefore the ground and flight testing can be reduced accordingly. Also, a thorough ground testing program should result in reduction in necessary flight testing. When the operating or airworthiness regulations require a system to pertorm its intended function, the use of TSO'd equipment or the submission of data substantiating the equipment performance is strongly recommended.
(2) Regulatory References. Sections 29.1301, 29.1309, 29.1329, 29.1331,
29.1333, 29.1355, 29.1431, 29.1457.
(3) System Design. Systems or equipment presented for installation approval, when not qualified by TSO or other approval means, should be accompanied by sufficient data to substantiate their design acceptability.
Operation of Controls. The operation of controls intended for use during flight, in all possible position combinations and sequences, should not result in a condition that would be detrimental to the continued safe performance of the system.
(!) Electrical Shock. Systems should be designed so that under all probable conditions the risk of dangerous electrical shock is minimized.
(iii) Fire Hazard. The design of the system should be such that all components meet the applicable fire and smoke protection requirements of §$ 29.853 and 29.863. Cables and equipment to be installed in designated fire zones, that are used during emergency procedures should be at least fire resistant.
(IV) Plugs and Cables. Connector pins for sensitive signal circuits should not be adjacent to pins used for AC power circuits. When redundant wiring is used to comply with the systems independence regulations such as §§ 29.1331, 29.1333, or
29.1355, the wires should be routed through separate plugs and/or cables with as much physical separation as practicable. The system should be designed so that incorrect mating of plugs is not possible. Cable grounding and shielding techniques should be used to minimize electromagnetic interference.
1192 Par 776
(4) System Performance. Where the operating or airworthiness regulations require a system to perform its intended function, and when the equipment is not qualified by TSO or other approval means, performance data furnished to the FAA/AUTHORITY can reduce the installed performance testing. The appropriate TSO minimum performance standard may be used as a guide.
Environment. An appropriate means for environmental testing is set forth in Radio Technical Commission for Aeronautics (RTCA) document DO-160. The applicant should submit test reports showing that the laboratory tested categories such as temperature, vibration, altitude, etc., are compatible with the environmental demands to be placed on the rotorcraft.
(її) Failure Analysis. Procedures are contained in Paragraph 621, Section c of this advisory circular.
(5) Installation Design Mechanical Installation. Installations should be made to (1) ensure compliance with the airworthiness regulations and (2) comply with the equipment manufacturer's recommendations. The designer should observe good engineering practices in specifying material type, thickness, fastener type, edge distance, and attachment to the equipment rack. By analysis or static tests the mounted equipment should be shown to withstand the inertia forces of §§ 29.561(b)(3) and 29.337. Refer to AC 43.13-2a for static test procedures.
(її) Arrangement and Visibility. The mounting position of all instruments, switches, position labels, and control heads should make them plainly visible to the pilot while in his normal panel-facing position and under all cockpit lighting conditions likely to occur. TSO approval does not assure instruments will be acceptable in a particular cockpit installation or for all lighting conditions. The instruments, switches, and placarding must be free from reflections. Malfunction annunciation devices should be conspicuous and clearly visible to the pilot. (See Advisory Circular 20-69 and §§ 29.1321, 29.771, 29.1381, and 29.1555(a).)
Load Analysis.
(A) Power Sources. It should be determined whether the electrical power source capacity is adequate for the system installation under all foreseeable operating conditions including engine failure on multiengine rotorcraft. System load reductions should be applied or power source capacity increased if necessary to assure compatibility between load and source. Duplicate systems should be powered from separate buses and, in some cases, from independent sources if required by the airworthiness regulations. (Sections 29.1309, 29.1331, 29.1333, 29.1351, or 29.1355.)
Par 776 1193
АС 29-2B 7/30/97 (B) Navigation Course Deviation Circuit Loading. It should be determined that the deviation circuit source impedance is matched by its load and that the source capacity is not exceeded. When the system is capable of transfer, the transfer loads should also be considered (§ 29.1301).
(C) Malfunction Indicator Circuit Loading. It should be determined that the malfunction indicator source impedance is matched by its loads and that the source capacity is not exceeded. When the system is capable of transfer, the transfer loads should also be considered (§ 29.1301).
(D) Synchro Signal Loading. When parallel loads are added to Synchro's, the manufacturers' specifications should be reviewed to assure that the additional loads do not result in an overloaded synchro.
(iv) Interface. In many cases, the mating units of a system are designed by different manufacturers. For example, a brand-X gyro may be designed for operation with a brand-X flight director, but later a modifier decides to operate a brand-Y autopilot with the brand-X gyro. This applies just as well to NAV receivers, AREA NAV units, course indicators, omni bearing selectors, tachometer indicators, transmitters and many other equipment items. When this is the case, the applicant should provide data, in summarized form, describing those characteristics such as impedance, volts, etc., that are necessary to assure a compatible and reliable system.
The data should also reference the source of the interface data (§ 29.1301).
(V) Flight Tests. An FAA/AUTHORITY engineering flight test is required during type certification or after modification that changes the established limitations, flight characteristics or performance of a rotorcraft or any of its required systems or operating procedures. New installations of equipment in the cockpit or modifications that affect existing equipment in the cockpit should be evaluated by appropriate flight test personnel, if it is necessary to evaluate operational aspects of the change. Where possible, cockpit arrangement, placards, markings, instrument visibility, and light reflections can be evaluated on the ground if the applicant opts to darken the windows.
Electromagnetic compatibility functional checks, windshield glare, and pilot workload evaluations may be conducted in flight at the FAA/AUTHORITY flight test pilot's option.
(vi) Radio Master Switches. Some installations incorporate radio master switches to control special busses for the avionics systems. If this capability is provided it should be evaluated to assure failure modes are not introduced that will result in excessive or even total loss of all required avionics. One switch that controls all required avionics is not considered acceptable for IFR installations. The evaluation should include an assessment of the loss of the systems to be included on the radio master switches), and the subsequent effect on continued safe flight.
b. Test Procedures. Where the airworthiness or operating regulations require a system to perform its intended function, and/or not create a hazard to other required 1194 Par 776
systems, sufficient testing should be accomplished to assure satisfactory performance.
When ground testing is not sufficient to properly evaluate a system's performance, flight testing should be accomplished. Acceptable flight test criteria for specific navigation and communication equipment are contained herein. If the rotorcraft is to be approved for IFR operations, the additional criteria of Paragraph 775 of this advisory circular should be satisfied.
(1) VHF Systems.
General. Intelligible communications should be provided between the rotorcraft and ground facilities throughout the airspace within 100 NM of an FAA/AUTHORITY ground facility from radio line of sight altitude to the maximum altitude for which the rotorcraft is certificated. Communication should be provided with the rotorcraft at or above line of sight altitude in right and left bank up to 10 degrees and on all headings.
(ii) Electromagnetic Compatibility (EMC). With all systems operating in flight, verify by observation that no adverse effects are present in the flight systems.
(¡i) Antenna Measurement. If satisfactory antenna measurement data are provided, the following flight test may be reduced to checks in right and left turns in the vicinity of the predicted bearings of worst performance. If antenna locations are symmetrical, tests may be conducted using only one direction of turn.
(A) Long Range Reception. Starting at a distance of at least 100 NM from the ground facility antenna, perform a right and/or left 360 degree turn at a bank angle of at least 10 degrees. Communicate with the ground facility every 10 degrees of turn to test the intelligibility of the signals received at the ground station and in the rotorcraft. For 100 NM, the minimum line of sight altitude is approximately 7,000 feet.
(B) Approach Configuration. With the landing gear down and with the rotorcraft in the approach configuration (at a distance of 10 NM from the ground station and in an idle power descent toward the station), demonstrate intelligible communications between the rotorcraft and the ground facility.
(2) HF Systems.
Acceptable communications should be demonstrated by contacting a ground facility at a distance of at least 100 nautical miles. Single sideband equipment should also perform acceptably in the amplitude modulation mode of operation.
(II) It should be demonstrated that precipitation static is not excessive when the aircraft is flying at cruise speed (in areas of high electrical activity, including Par 776 1195
clouds and rain if possible). Use the minimum amount of installed dischargers for which approval is sought.
(3) VOR Systems.
These flight tests may be reduced if adequate antenna radiation pattern studies have been made and these studies show the patterns to be without significant holes (with the rotorcraft configurations used in flight, i.e., landing gear retracted en route and extended for approach). Particular note should be made in recognition that certain rotor RPM settings may cause modulation of the course deviation indication (rotor modulation). VOR performance should be checked for rotor modulation in both approach and en route operation while varying rotor RPM throughout its normal range.
(Il) The airborne VOR system should operate normally with warning flags out of view at all headings of the rotorcraft (in level flight) throughout the airspace within 100 NM of the VOR facility while flying above the radio line of sight altitude to within 90 to 100 percent of the maximum altitude for which the rotorcraft is certified.
(Ili) The accuracy determination should be made such that the indicated reciprocals agree within 2 degrees. Tests should be conducted over at least two known points, on the ground, such that data are obtained in each quadrant. Data should correlate with the ground calibration and in no case should the absolute error exceed +6 degrees. Fluctuation of the course deviation indication should not be excessive.
(A) En route Reception. Fly from a VOR facility, rated for high altitude, along a radial to a range of 100 NM. The VOR warning flag should not come into view, nor should there be deterioration of the station identification signal. The course width should be 20 degrees (15 degrees tolerance, 10 degrees either side at the selected radial). If practical, perform en route segment on a doppler VOR station to verify the compatibility of the airborne unit. Large errors have been found when incompatibility exists.
(B) Long Range Reception. Perform a 360-degree right and a 360-degree left turn at a bank angle of at least 10 degrees at an altitude just above radio line of sight (see b(1) (ili)(A) for line of sight altitude) and at a distance of at least 100 NM from the VOR facility. Signal dropout should not occur as evidenced by the malfunction indicator appearance. Dropouts that are relieved by a reduction of bank angle at the same relative heading to the station are satisfactory. The VOR identification should be satisfactory during the left and right turns.
(C) En route Station Passage. Verify that the To-From indicator correctly changes as the rotorcraft passes through the cone of confusion above a VOR facility.
1196 Par 776
(4) Localizer Systems.
(i> Flight test requirements may be modified to allow for adequate antenna radiation pattern measurements as discussed under VOR Paragraph b(3)(i) flight test.
(il) The signal input to the receiver presented by the antenna system should be of sufficient strength to keep the malfunction indicator out of view when the rotorcraft is in the approach configuration and at least 10 NM from the station. This signal should be received for 360 degrees of rotorcraft heading at all bank angles up to 10 degrees left or right at all normal pitch altitudes, and at an altitude of approximately 2,000 feet.
(ill) The deviation indicator should properly direct the aircraft back to course when the rotorcraft is right or left of course.
(iv) The station identification signal should be of adequate strength and sufficiently free from interference to positive station identification, and voice signals should be intelligible with all electric equipment operating and pulse equipment transmitting.
(v) Localizer performance should be checked for rotor modulation in approach while varying rotor RPM throughout its normal range.
(A) Localizer Intercept. In the approach configuration and a distance of at least 10 NM from the localizer facility, fly toward the localizer front course, inbound, at an angle of at least 50 degrees. Perform this maneuver from both left and right of the localizer beam. No flags should appear during the time the deviation indicator moves from full deflection to oncourse. If the total antenna pattern has not been shown by ground checks or by VOR flight evaluation to be adequate, additional intercepts should be made.
(B) Localizer Tracking. While flying the localizer inbound and not more than 5 miles before reaching the outer marker, change the heading of the rotorcraft to obtain full needle deflection. Then fly the rotorcraft to establish localizer on course operation. The localizer deviation indicators should direct the rotorcraft to the localizer on course. Perform this maneuver with both a left and a right needle deflection. Continue tracking the localizer until over the transmitter. At least three acceptable front course and back course flights should be conducted to 200 feet or less above threshold.
(5) Glide Slope Systems.
Par 776 1197
Flight Test. The signal input to the receiver should be of sufficient strength to keep the warning flags out of view at all distances to 10 NM from the facility.
This performance should be demonstrated at all aircraft headings from 30 degrees left to 30 degrees right of the localizer course. The deviation indicator should properly direct the aircraft back to path when the aircraft is above or below path. Interference with the navigation operation should not occur with all rotorcraft equipment operating and all pulse equipment transmitting. There should be no interference with other equipment as a result of glide slope operation.
Glide Slope Intercept. While flying the localizer course inbound in level flight, intercept the glide slope below path at least 10 NM from the station.
Observe the glide slope deviation indicator for proper crossover as the aircraft flies through the glide path. There should be no flags from the time the needle leaves the full scale fly-up position until it reaches the full scale fly-down position.
Glide Slope Tracking. While tracking the glide slope, maneuver the aircraft through normal pitch and roll attitudes. The glide slope deviation indicator should show proper operation with no flags. At least three acceptable approaches to 200 feet or less above threshold should be conducted.
(iv) Interference. With all rotorcraft electrical equipment operating and all pulse equipment transmitting, determine that there is no interference with the glide slope operation (some interference from the VHF may be acceptable), and that the glide slope system does not interfere with other equipment.
(V) Glide slope performance should be checked for rotor modulation during the approach while varying rotor RPM throughout its normal range.
(6) Marker Beacon System.
(i) The marker beacon annunciator light should be illuminated for a period of time representing 2,000 to 3,000 feet distance when flying at an altitude of 1,000 feet as it passes over a marker beacon (see table below).
Altitude = 1,000 feet (AGL) Ground Speed Light Time (Seconds) Knots 2,000 feet 3,000 feet 90 13 20 110 11 16 130 14 150 12 1198 Par 776
(i) The audio signal should be of adequate strength and sufficiently free from interference to provide positive identification.
Technical: Approach the markers at a ground speed of 130 knots and at an altitude of 1,000 feet above ground level. While passing over the outer and middle markers with the localizer deviation indicator centered, the annunciators should be illuminated for a period of 9 to 14 seconds. Check for acceptable intensity of the indicator lights in bright sunlight and at night. For slower rotorcraft, the interval should be proportionately longer.
NOTE: It is recognized that the normal altitude at the middle marker is on the order of 150 to 200 feet. Due to variations in both glide slope angle and position of the middle marker in relation to the runway, the on glide path marker width will vary considerably which in turn will give a widely varying light time. Therefore, the more clearly defined criteria at 1,000 feet altitude should be used for quantitative testing of the middle marker function.
(7) Automatic Direction Finding Equipment (ADE).
Range and Accuracy. The ADF system installed in the rotorcraft should provide operation with errors not exceeding 5 degrees and the aural signal should be clearly readable up to the distance listed for any one of the following types of radio beacons:
(A) 50 NM from an H facility (transmitter power 50-2,000 watts).
(B) 25 NM from an MH facility (transmitter power less than 50 watts).
(C) 15 NM from a compass locator (transmitter power less than 25 watts).
(ii) Needle Reversal. The ADF indicator needle should make only one 180-degree reversal when the rotorcraft flies over a radio beacon. This test should be made both with and without the landing gear extended.
(iii) Indicator Response. When switching stations with relative bearings differing by approximately 175 degrees, the indicator should indicate the new bearing within +5 degrees within 10 seconds.
(iv) Antenna Mutual Interaction. For dual installations, there should not be excessive coupling between the antennas.
(v) Technique.
Par 776 1199