AC 27-1B, Chg 7 2/4/2016
(iv) Plugs and Cables. Connector pins for sensitive signal circuits should not be adjacent to pins used for ac power circuits. If redundant wiring is used to comply with systems regulations such as § 27.1309, the wires should be routed through separate plugs or cables with as much physical separation as practicable. The system design should eliminate possible incorrect mating of plugs. Minimize electromagnetic interference by using cable grounding and shielding techniques.
(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 useful as a guide.
(i) Environment. An appropriate means for environmental testing is set forth in Radio Technical Commission for Aeronautics (RTCA) Document DO-160. Applicants should submit test reports showing that the laboratory-tested categories, such as temperature, vibration, altitude, etc., are compatible with the environmental demands placed on the rotorcraft.
(ii) Failure Analysis. Section 27.1309(b) requires consideration of system malfunctions or failures.
(5) Installation Design.
(i) Mechanical Installation. Installations should ensure compliance with airworthiness regulations and 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 §§ 27.561(b)(3) and 27.337. Refer to AC 43.13-2 (current version) for static test procedures.
(ii) 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 §§ 27.1321, 27.771, 27.1381,
27.1555(a) and AC 20-69.)
(iii) 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. Apply system load Page MG 1 -2
reductions or increase power source capacity, if necessary, to assure compatibility between load and source. If duplicate systems are required, power them from separate buses.
(B) Navigation course deviation circuit loading. It should be determined that its load matches the impedance of the deviation circuit source and does not exceed the source capacity. Consider the transfer loads when the system is capable of transfer (§ 27.1301).
(C) Malfunction indicator circuit loading. It should be determined that its load matches the impedance of the malfunction indicator source and does not exceed the source capacity. Consider the transfer loads when the system is capable of transfer (§ 27.1301).
(D) Synchro signal loading. When adding parallel loads to synchros, review the manufacturers’ specifications to assure that the additional loads do not result in an overloaded synchro.
(iv) Interface. In many cases, different manufacturers design the mating units of a system. 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 navigational (NAV) receivers, Area NAV (RNAV) 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 ensure a compatible and reliable system.
The data should also reference the source of the interface data (§ 27.1301).
(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. Appropriate flight test personnel should evaluate new installations of equipment in the cockpit or modifications that affect existing equipment in the cockpit, if it is necessary to evaluate operational aspects of the change. If the applicant opts to darken the windows, evaluate the cockpit arrangement, placards, markings, instrument visibility, and light reflections on the ground, where possible.
Conduct electromagnetic compatibility functional checks, windshield glare, and pilot workload evaluations 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 providing this capability, evaluate it to ensure no introduction of failure modes that will result in excessive or even total loss of all required avionics. One switch that controls all required avionics is unacceptable for instrument flight rules (IFR) installations. The evaluation should include an assessment of the loss of the systems to be included on the radio master switch(es), and the subsequent effect on continued safe flight.
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AC 27-1B, Chg 7 2/4/2016
b. Test Procedures. Where the airworthiness or operating regulations require a system to perform its intended function, and not create a hazard to other required systems, accomplish sufficient testing to ensure satisfactory performance. When ground testing is not sufficient to evaluate a system’s performance properly, accomplish flight testing. Acceptable flight test criteria for specific navigation and communication equipment are contained herein. If seeking IFR operations approval for the rotorcraft, satisfy the additional criteria of section AC 27 Appendix B of this AC.
(1) VHF Systems.
(i) General. Provide intelligible communications between the rotorcraft and ground facilities throughout the airspace within 80 nautical miles (NM) of an FAA/AUTHORITY ground facility from radio line of sight altitude to the maximum altitude for which the rotorcraft is certificated. Provide communication with the rotorcraft at or above line of sight altitude in right and left bank up to 10° 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.
Complete a qualitative evaluation of VHF radio navigation and communication equipment operation. Further guidance may be found in AC 43.13-2B, Chapter 2, paragraph 209.
(iii) Antenna Measurement. If provided satisfactory antenna measurement data, reduce the following flight test to checks in right and left turns near the predicted bearings of worst performance. If antenna locations are symmetrical, conduct tests using only one turn direction.
(A) Long range reception. Starting at a distance of 80 NM from the ground facility antenna, perform a right or left 360° turn at a bank angle of at least 10°.
Communicate with the ground facility every 10° of turn to test the intelligibility of the signals received at the ground station and in the rotorcraft. For 80 NM, the minimum line of sight altitude is approximately 4,000 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.
(i) Demonstrate acceptable communications by contacting a ground facility at a distance of at least 80 NM. Single sideband equipment should also perform acceptably in the amplitude modulation mode of operation.
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(ii) Demonstrate that precipitation static is not excessive when the aircraft is flying at cruise speed (in areas of high electrical activity, including clouds and rain if possible). Use the minimum number of installed dischargers.
(3) Very High Frequency Omnidirectional Range (VOR) Systems.
(i) Reduce these flight tests if adequate studies of antenna radiation pattern have shown 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). Make particular note to recognize 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.
(ii) 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 80 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.
(iii) The indicated reciprocals accuracy determination should agree to within 2°. Conduct the tests over at least two known points on the ground to obtain data in each quadrant. Data should correlate with the ground calibration with no absolute error exceeding ±6°. Fluctuation of the course deviation indication should not be excessive.
(A) Enroute Reception. Fly from a VOR facility along a radial to a range of 80 NM. The VOR warning flag should not come into view nor should the station identification signal deteriorate. The course width should be 20° (±5° tolerance, 10° 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. There have been large errors when incompatibility exists.
(B) Long range reception. Perform a 360° right and a 360° left turn at a bank angle of at least 10° at an altitude just above radio line of sight (see paragraph
b.(1)(iii)(A) above for line of sight altitude) and at a distance of 80 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) Enroute station passage. Verify that the To -From indicator correctly changes as the rotorcraft passes through the cone of confusion above a VOR facility.
(4) Localizer Systems.
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AC 27-1B, Chg 7 2/4/2016
(i) Flight test requirements may be modified to allow for adequate antenna radiation pattern measurements as discussed under VOR systems, paragraph b.(3)(i) above.
(ii) 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° of rotorcraft heading at all bank angles up to 10° left or right at all normal pitch altitudes, and at an altitude of approximately 2,000 feet.
(iii) 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°. 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 on course. If the total antenna pattern are not been shown to be adequate by ground checks or by VOR flight evaluation, 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. Conduct at least three acceptable front and back course flights to 200 feet or less above threshold.
(5) Glide Slope Systems.
(i) 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.
Demonstrate this performance at all aircraft headings from 30° left to 30° 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 because of glide slope operation.
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(ii) 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. No flags should appear between the times the needle leaves the full-scale fly-up position and it reaches the full-scale fly-down position.
(iii) 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. Conduct at least three acceptable approaches to 200 feet or less above threshold.
(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 as follows:
Altitude = 1,000 feet (AGL) Ground Speed Light Time (Seconds) Knots 2,000 feet 3,000 feet 90 13 20 110 11 16 130 9 14 150 8 12
(ii) The audio signal should be of adequate strength and sufficiently free from interference to provide positive identification.
(iii) 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 illuminate for 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.
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AC 27-1B, Chg 7 2/4/2016 Note: We recognize that the normal altitude at the middle marker is approximately 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, use the more clearly defined criteria at 1,000-feet altitude for quantitative testing of the middle marker function.
(7) Automatic Direction Finding Equipment (ADF).
(i) Range and Accuracy. The ADF system installed in the rotorcraft should provide operation with errors not exceeding 5° 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 homing (H) facility (transmitter power at 50-2,000 watts).
(B) 25 NM from an medium homing (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° reversal when the rotorcraft flies over a radio beacon. Make this test both with and without the landing gear extended.
(iii) Indicator Response. When switching stations with relative bearings differing by approximately 175°, the indicator should indicate the new bearing within ±5° within 10 seconds.
(iv) Antenna Mutual Interaction. For dual installations, there should not be excessive coupling between the antennas.
(v) Technique.
(A) Range and accuracy. Tune in a number of radio beacons spaced throughout the 200 to 415 kHz range and located at distances near the maximum range for the beacon (see paragraph b.(7)(i), Range and Accuracy, above). The identification signals should be clear and the ADF should indicate the approximate direction to the stations. Beginning at a distance of at least 15 NM from a compass locator in the approach configuration, fly inbound on the localizer front course and make a normal instrument landing system (ILS) approach. Evaluate the aural identification signal for strength and clarity and the ADF for proper performance with the receiver in the ADF mode. All electrical equipment on the aircraft should be operating and all pulse equipment should be transmitting. Fly over a ground check point with relative bearings Page MG 1 -8
to the facility of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°. The indicated bearings to the station should correlate within 5°.
(B) Needle reversal. Fly the aircraft over an H, LOM, or LMM facility at an altitude of 1,000 to 2,000 feet above ground level. The indicator needle should make only one reversal.
(C) Indicator response. With the ADF indicating station dead ahead, switch to a station having a relative bearing of approximately 175°. It should indicate within ±5° of the bearing in not more than 10 seconds.
(D) Antenna mutual interaction. If testing a dual ADF installation, check for coupling between the antennas by using the following procedure.
(1) With #1 ADF receiver tuned to a station near the low end of the ADF band, tune the #2 receiver slowly throughout the frequency range of all bands and determine whether the #1 ADF indicator is adversely affected.
(2) Repeat paragraph b.(7)(v)(A) above, with #1 ADF receiver tuned to a station near the high end of the ADF band.
(8) Distance Measuring Equipment (DME).
(i) The DME system should:
(A) Continue to track without dropouts when maneuvering the rotorcraft throughout the air space within 80 NM of the VORTAC station and at altitudes from the radio line of sight to the maximum altitude for which the rotorcraft is certificated. Meet this tracking standard with the rotorcraft in the cruise configuration, at bank angles up to 10°, climbing and descending at normal maximum climb and descent attitude, and orbiting a DME facility.
(B) Provide clearly readable identification of the DME facility.
(C) DME operation should not interfere with other systems aboard the rotorcraft (some interference with the transponder may be acceptable), and DME operation should not be adversely affected by other equipment.
(D) Continue to operate and track when DME HOLD is activated and the channel switch is varied.
(E) Demonstrate proper operation when an override switch is provided.
(ii) Technique.
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AC 27-1B, Chg 7 2/4/2016 (A) Long range reception. Perform two 360° turns, one to the right and one to the left, at a bank angle of 8° to 10° at least 80 NM from the DME facility. A single turn will be sufficient if the antenna installation is symmetrical. There should be no more than one unlock, not to exceed one search cycle (maximum 35 seconds), in any 5 miles of radial flight.
(B) Approach. Make a normal approach to land at a field with a DME located on the airport. The DME should track without an unlock (station passage excepted).
(C) DME hold. With the DME tracking, activate the DME hold function.
Change the channel selector to a localizer frequency. The DME should continue to track on the original station.
(9) Transponder Equipment.
(i) Performance Criteria. The ATC transponder system should furnish a strong and stable return signal to the interrogating radar facility when flying the rotorcraft in straight and level flight throughout the air space within 80 NM of the radar station from radio line of sight to within 90 to 100 percent of the maximum altitude for which the rotorcraft is certificated. The airborne system should be controllable so that objectionable ring-around, spoking, and clutter will not persist. The transponder system should not interfere with other systems aboard the rotorcraft and other equipment should not interfere with the operation of the transponder system (some interference from DME operation may be acceptable). When flying the rotorcraft in the following maneuvers within the airspace described above, the dropout time should not exceed 20 seconds.
(A) In turns at bank angles up to 10°.
(B) Climbing and descending at normal maximum climb and descent attitude.
(C) Orbiting a radar facility.
(ii) Technique.
(A) Climb and distance coverage. Beginning at a distance of at least 10 NM from and at an altitude of 2,000 to 3,000 feet above that of the radar facility and using a transponder code assigned by the ARTCC, fly on a heading that will pass the rotorcraft over the facility. At a distance of 5 to 10 NM beyond the facility, operate the rotorcraft to maintain an altitude above radio line of sight while maintaining the aircraft at a heading within 5° from the radar facility to 80 NM from the radar facility.
(B) Communicate with the ground radar personnel for evidence of transponder dropout. During the flight, check the ”ident” mode of the ATC transponder Page MG 1 -10
to assure that it is performing its intended function. Determine that the transponder system does not interfere with other systems (except possibly the DME) aboard the rotorcraft and that other equipment (except possibly the DME) does not interfere with the operation of the transponder system. There should be no dropouts, that is, when there is no return for two or more sweeps. Verify the operation of the ATC transponder over the station at 25 NM and at 80 NM.
(C) Long range reception. Perform two 360° turns, one to the right and one to the left, at bank angles of 8° to 10° with the flight pattern 80 NM from the radar facility. During these turns, monitor the radar display to ensure there are no signal dropouts (two or more sweeps).
(10) Weather Radar Equipment.
(i) Bearing Accuracy. The indicated bearing of objects shown on the display should be within 5° of their actual magnetic bearing within the sectors 40° right and left of the aircraft longitudinal axis. Beyond 40° right and left, bearing accuracy should be ±10°.
(ii) Distance of Operation. The radar should be capable of displaying prominent targets throughout the distance and angular range of the display.
(iii) Antenna Stabilization. When providing antenna stabilization, it should eliminate blurring of the display for its designed ranges of pitch and roll.
(iv) Beam Tilting. Install the radar antenna so that its beam is adjustable to any position between 10° above and 10° below the plane of rotation of the antenna.
(v) Technique.
(A) Bearing Accuracy. Fly under conditions that allow visual identification of a target, such as an island, a river, or a lake, at a range within 10 percent of the maximum range of the radar. When flying toward the target, select a course that will pass over a reference point with a known bearing to the target. When flying a course from the reference point to the target, determine the error in displayed bearing to the target on all range settings. Change heading in increments of 10° and determine the error in the displayed bearing to the target.
(B) Contour display (iso echo). If there are reports of heavy cloud formations or rainstorms within a reasonable distance from the test base, select the contour display mode. The radar should differentiate between heavy and light precipitation. In the absence of the above weather conditions, determine the effectiveness of the contour display function by switching from normal to contour display while observing large objects of varying brightness on the indicator. The brightest objects should become the darkest when switching from normal to contour mode.
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AC 27-1B, Chg 7 2/4/2016 (C) Stability. While observing a target return on the radar indicator, turn off the stabilizing function, then put the aircraft through pitch and roll movements.
Observe the blurring of the display. Turn the stabilizing mechanism on, then repeat the roll and pitch movements. Evaluate the effectiveness of the stabilizing function in maintaining a sharp display.
(D) Ground mapping. Fly over areas containing large, easily identifiable landmarks such as rivers, towns, islands, coastlines, etc. Compare the form of these objects on the indicator with their actual shape as visually observed from the cockpit.
(E) Mutual interference. Determine that no objectionable interference is present on the radar indicator from any electrical, radio, or navigational equipment when operating, and that the radar installation does not interfere with the operation of any of the rotorcraft’s radio or navigational systems.
(11) Area Navigation. ACs 20-138 and 90-100 (current versions) contain the basic criteria for evaluating an area navigation system, including acceptable means of compliance to the Federal Aviation Regulations.
(12) Inertial Navigation. AC 20-138 (current version) is the basic criteria for the engineering evaluation of an inertial navigation system (INS) and offers acceptable means of compliance with the applicable FA Regulations, which contain mandatory requirements in an objective form. For flights up to 10 hours, the radial error should not exceed two NM per hour of operation on a 95 percent statistical basis. For flights longer than 10 hours, the error should not exceed ±20 NM cross-track or ±25 NM along track error. A circle represents the two NM radial errors having a radius of two NM, centered on the selected destination point.
(13) Doppler Navigation. Evaluate doppler navigation system installed performance in accordance with RTCA Document DO-158, “Minimum Performance Standards – Airborne Doppler Radar Navigation Equipment.”
(14) Radio Altimeters. Evaluate radio altimeter system installed performance in accordance with RTCA Document DO-155 (current version).
(15) Emergency Locator Transmitters (ELT).
(i) Evaluate ELT performance in accordance with TSO-C126. Examine ELT installations for potential operational problems. There have been numerous instances of interaction between ELT and other VHF installations. ELT antenna installations in close proximity to other VHF antennas should be suspect. Measure the patterns of previously installed VHF antennas after an ELT installation. Some problems caused by ELT installations are:
(A) Loss of radiated power from VHF communications.
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(B) Reradiation of VHF transmitter energy such that navigation crosspointers are affected.
(C) Reception of FM broadcast, at high level, in VHF communications.
(D) Inadvertent activation of the ELT by VHF transmitted energy (see AD 72-22-3.)
(ii) ELT installation. TSO -C126 specifies that the ELT be automatically activated when subjected to a force of 5.0(±2, -0)g in the direction of the longitudinal axis of the aircraft. We consider this mounting recommendation satisfactory for rotorcraft. In recognition of the significant vertical impact velocity that rotorcraft commonly have, an optional placement of the ELT pitched down 30° from the horizontal axis of the rotorcraft is also satisfactory.
(16) Audio Interphone Systems. Demonstrate acceptable communications for all audio equipment including microphones, speakers, headsets, and interphone amplifiers.
Test all modes of operation, including operation during emergency conditions (i.e., emergency descent, and oxygen masks) with all rotorcraft engines running, all rotorcraft pulse equipment transmitting, and all electrical equipment operating.
(17) Portable Battery Powered Megaphones. Evaluate megaphone performance in accordance with AC 121-6.
(18) Global Positioning System (GPS)/Satellite-Based Augmentation System (SBAS) Wide Area Augmentation System (WAAS). GPS installations in rotorcraft can, depending on other installed equipment, result in significant changes in the aircraft’s operational capabilities. Installation of stand-alone GPS navigators not integrated with any other aircraft systems can be straightforward and simple. AC 20-138 (current version), Chapter 14 contains information on GPS/SBAS installations. The following elaborates on and takes precedence over the means of compliance referenced in AC 20-138 (current version) for rotorcraft installations. If considering point in space approaches using WAAS (SBAS) capabilities, it may be helpful to review of RTCA Document DO-229 (current version).
(i) Installations that integrate with existing primary flight and navigation instruments to provide flight guidance to the pilot may be more complex and require more testing and evaluation to ensure the integration performs its intended function.
Integration of GPS with an AFCS is more complex and requires more testing and evaluation. Installation of GPS-WAAS requires evaluation of integration between the GPS, autopilot, and flight director (if installed).
(ii) Consider installation of GPS-WAAS with the intent of allowing steep angle or low speed approaches and accomplish through the STC process.
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