(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 time the needle leaves the full scale fly-up position until 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. 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 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 29-2C, 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, 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 (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 a homing (H) facility (transmitter power at 50-2,000 watts).
(B) 25 NM from a 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 - 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 to the facility of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°. The indicated bearings to the station should correlate within 5°.
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(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 100 NM of the VORTAC station and at altitudes from the radio line of sight to the maximum altitude for which the rotorcraft is certificated. This tracking standard should be met 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.
(A) Climb and maximum distance. Determine that there is no mutual interference between the DME system and other equipment aboard the rotorcraft.
Beginning at a distance of at least 10 NM from a DME facility and at an altitude of Page MG 1 - 9
AC 29-2C, Chg 7 2/4/2016 2,000 feet above the DME facility, fly the rotorcraft on a heading so that the aircraft will pass over the facility. At a distance of 5 to 10 NM beyond the DME facility, operate the rotorcraft at its normal maximum climb attitude up to an altitude of 7,000 feet maintaining the aircraft on a station radial (within 5°). The DME should continue to track with no unlocks to a range of 100 NM. Record the maximum altitude flown.
(B) 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 100 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.
(C) Penetration. From an altitude above 7,000 feet (AGL), perform a let-down directly toward a ground station (DME facility) at a normal maximum rate of descent to reach an altitude of 5,000 feet above the DME facility 5 to 10 NM before reaching the DME facility. The DME should continue to track during the maneuver with no unlocks.
(D) 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).
(E) 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 100 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 controllabl e 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 air space 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.
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(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 100 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 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. The operation of the ATC transponder should be verified over the station, at 25 NM, and at 100 NM.
(C) Long range reception. Two 360° turns, one to the right and one to the left, at bank angles of 8 to 10° with the flight pattern should be performed at least 100 NM from the radar facility. During these turns, the radar display should be monitored 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. The radar antenna should be installed 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 Page MG 1 - 11
AC 29-2C, Chg 7 2/4/2016 pass over a reference point from which the bearing to the target is known. 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.
(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 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 Federal Aviation 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 crosstrack or ±25 NM along track error. A 2-nautical-mile radial error is represented by a circle, having a radius of 2 nautical miles, centered on the selected destination point.
(13) Doppler Navigation. Doppler navigation system installed performance may be evaluated in accordance with RTCA/DO-158, Minimum Performance Standards – Airborne Doppler Radar Navigation Equipment.
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(14) Radio Altimeters. Radio altimeter system installed performance may be evaluated in accordance with RTCA Document DO-155 (current version).
(15) Emergency Locator Transmitters (ELT).
(i) Emergency locator transmitter performance may be evaluated 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.
(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 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.
All modes of operation should be tested, 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. Megaphone performance should be evaluated 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 guidance Page MG 1 - 13
AC 29-2C, Chg 7 2/4/2016 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) Installation of GPS-WAAS with the intent of allowing steep angle or low speed approaches are considered a major change and should be accomplished through the STC process.
(iii) Display Integration. The following takes precedence over AC 20-138 (current version) guidance.
(A) Arrangement and visibility.
(1) For rotorcraft installations, section 29.1321 of this AC defines the line of sight and fields of view.
(2) Display of required information (see AC 20-138 (current version) and Society of Automotive Engineer (SAE) Aerospace Recommended Practice (ARP) 4102-7). Like other navigation systems, display the information necessary for the pilot to use the system for its intended function. If providing integration with an autopilot and flight director system, then display the coupled or selected flight director modes in the pilot’s primary field of view. In addition to guidance in AC 20-138, display the following information in the pilot’s primary field of view:
(i) GPS level of service (localized performance with vertical guidance (LPV), lateral navigation/vertical navigation (LNAV/VNAV), LNAV, etc.).
(A) Display other modes not specific to an approach line of minima (i.e., proprietary modes like advisory vertical guidance).
(B) Display mode changes due to degraded GPS capabilities.
(ii) GPS waypoint information.
(A) Waypoint name or identifier.
(B) Distance to and from waypoint.
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(iv) GPS alerts and messages (e.g., “SUSPEND,” “MSG”), and any malfunction or downgraded capabilities.
(3) For GPS systems that provide “advisory” vertical guidance, the vertical guidance cueing and symbology should be distinct enough to discriminate it from LPV or ILS vertical guidance. Evaluate the coupling of the autopilot to an advisory glideslope.
(B) Color.
(1) Color philosophy should match the philosophy used on primary flight display and other electronic displays.
(2) For analog displays, colors used in remote annunciation panels should match those used by the GPS manufacturer.
(iv) Flight Test.
(A) Conduct flight evaluations of the GPS, autopilot, and flight guidance system function together, as required, to ensure integration. Additionally, if use for steep angle point in space (PINS) or other specialized uses are envisioned, flight evaluations are needed to ensure the integration of the activities coupled with the handling characteristics of the aircraft provides the capability to perform the approaches without undue concentration or excessive workload on the part of the pilot. See AC 20-138 (current version), Chapter 20 for further guidance.
(B) Steep angle (> 4 degrees glide path angle), low speed (<70kts KIAS) approaches should be evaluated for IFR certificated aircraft.
(1) Evaluate:
(i) Aircraft handling in different coupled modes at the rotorcraft Vmini at critical CG.
(ii) Steepest glide path angles requested at each of the coupled modes used (see section AC 29, Appendix B of this AC for glide path angle limitations and Vmini).
(iii) For three axis autopilots, assess pilot workload and autopilot capabilities in all coupled modes used for steep approaches.
(iv) For four axis autopilots, assess pilot workload and autopilot capabilities in all coupled modes.
(v) Assess pilot workload with pilot hand flying:
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AC 29-2C, Chg 7 2/4/2016 (A) Minimum equipment required for IFR flight.
(B) Flight director modes, if installed.
(vi) Assess pilot workload, pilot-system interface on missed approaches terminating at the holding fix.
(vii) Abuse testing should include:
(A) Deviation from glidepath and lateral course on intermediate and the final approach segments.
(a) Deviations should be at least one dot laterally and one dot vertically.
(b) Approach segment flight path and glide path should be recaptured and stabilized prior to the final approach fix (FAF) for the intermediate segment and the Missed Approach Point (MAP) for the final segment.
(c) Vertical speed in the descent should be less than 1,000 fpm.
(d) Torque values should be high enough to keep from entering autorotation.
(e) The pilot should have enough time to easily transition to the visual segment (B) Ability to maintain airspeed at or below the maximum airspeed for the approach.
(C) Maximum allowable tail winds (many steep angle approaches have only one inbound course).
(D) Effect of approach downgraded from LPV to LNAV before and after the FAF, which may require either continuation of the approach or execution of a missed approach.
(viii) Assess the pilot workload and procedures, with autopilot coupled, on complete approaches using transition waypoints and vectors-to-final.
(A) For steepest glide path angle and approach airspeed for which approval is requested.
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(B) Assess the handling qualities with the autopilot coupled. If a 4-axis autopilot is proposed, then evaluate the loss of each axis on approach procedures and aircraft handling characteristics.
(C) Assess the transition from coupled instrument flight to uncoupled visual flight at the Decision Altitude (DA).
(a) Accomplish the continuation of the approach in the visual mode to assess the workload required to slow the aircraft at a point to make a landing.
(b) For rotorcraft with Category A procedures, ensure the aircraft can slow to the appropriate speed by the designated landing decision point from the DA.
(ix) If not evaluating the steep angle approaches for IFR aircraft, then a limitation should be added to the rotorcraft flight manual or rotorcraft flight manual supplement limiting IFR coupled RNAV approach operations to a maximum glidepath angle of 3.5° and the minimum approach airspeed that meet flight manual limitations. This is necessary until evaluations are accomplished and the determination is made that the autopilot-GPS integration supports steep-angle, low speed operations.
(2) Failure mode evaluations:
(i) Evaluate the loss of SBAS and all flight director or vertical guidance display behavior during all phases of operation.
(A) Indications of failure of the SBAS or loss of vertical guidance should be clear and unambiguous to the pilot.
(B) The pilot should be able to transition to degraded approach procedures without undue concentration or exceptional skill.
(ii) Evaluate misleading guidance information. Evaluate performance of advisory vertical guidance provided for LNAV approaches when provided in accordance with AC 20-138 (current version) guidance.
(19) Rotorcraft Condition Monitoring System Installations.
(i) General. Avionics equipment and systems are being installed in rotorcraft to collect data for use in assessing engine and rotorcraft performance and frequency of maintenance. Some of the items monitored are engine operating exceedances, hot starts, power assurance, and cycle counts. The monitoring systems addressed by this paragraph are those used to collect data for maintenance purposes and not those used in autopilot, flight control, or engine control systems. At present, optional approvals are being requested for most of these systems not performing any required functions.
However, most of the applicants anticipate requesting approval for the systems to be Page MG 1 - 17
AC 29-2C, Chg 7 2/4/2016 used in the future to perform some required function or to allow required maintenance to be predicated on the operation of the system. This consideration becomes particularly important if the system is software based. A further discussion of system software is included in paragraph b.(19)(iii)(B) below. Refer to section AC 29 MG 15 of this AC for guidance on certification of these systems, also referred to as Health Usage Monitoring Systems (HUMS).
(ii) System Installation. Show that system installations are free from hazards for both normal operation and possible malfunctions. Malfunctions which might be caused by software errors are discussed under paragraph b.(19)(iii)(B) below. The accuracy and response of the monitoring device or system should be sufficient to allow the operational and maintenance personnel to relate the data obtained to required maintenance actions. Use the exceedance (engine limit) information acquired by these systems in place of information previously acquired from field reports of operational personnel utilizing the basic aircraft instruments. In this case, the automated system will generally produce results, which are more accurate than the basic aircraft instruments. However, in this circumstance, it is not appropriate to require the monitor system to be more accurate than the previously approved methods used to provide the required exceedance data. If the data collected by the system require filtering prior to use, it is equally acceptable to accomplish this filtering either as the data are being acquired (airborne function) or when the data are analyzed (ground based function) and used in the maintenance of the rotorcraft.
(iii) System Components.
(A) Hardware. The hardware of the system, when operating under the control of the imbedded software, should be shown to comply with § 29.1301.
Additionally, in showing compliance to § 29.1309(a), laboratory testing to the appropriate portions of RTCA Document DO-160 (current version) should be performed.
(B) Software. If the function of the monitor system depends on embedded airborne software to determine all or part of its functioning, RCTA Document DO-178 (current version) is the recommended standard to be used for the approval of the system software. A further discussion of the use of this document is included in section
29.1309 of this AC. Carefully consider the selection of the software level because system approval is sometimes initially sought on the basis of the system being a non-required optional system. Further, if there is no dependence on the system software to preclude a hazardous failure mode, then a low software level would be acceptable. However, once initially certificated, it is very difficult to qualify software to higher levels of “quality.” Because of this, we recommend choosing the software at a level consistent with that of the ultimate use for the planned system approval. If the system approval is only to be as non-required optional equipment, then the choice of a low level of software qualification may be appropriate. However, when more experience is gained with the operation of the system, and it is ultimately planned to seek approval to perform required functions, then an appropriate higher level of software should be initially obtained.
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