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.
Page MG 1 -9
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.
(Il) 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.
(ili) 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.
Page MG 1 -11
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).
(1) 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.
Page MG 1 -12
(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.
Page MG 1 -13
AC 27-1B, Chg 7 2/4/2016
(iii) Display Integration. The following takes precedence over AC 20-138 (current version) guidance.
(A) Arrangement and visibility.
(1) For rotorcraft installations, section 27.1321 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/NAV), LNAV, etc.).
(A) Annunciate other modes not specific to an approach line of minima (i.e., proprietary modes like advisory vertical guidance).
(B) Annunciate mode changes due to degraded GPS capabilities.
(i) GPS waypoint information.
(A) Waypoint name or identifier.
B) Distance to and from waypoint.
(iii) 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 glides ope.
(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.
Page MG 1 -14
(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:
(1) Aircraft handling in different coupled modes at the rotorcraft Vmini at critical CG.
(I) Steepest glide path angles requested at each of the coupled modes used (see section AC 27, 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:
(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.
Page MG 1 -15
AC 27-1B, Chg 7 2/4/2016
(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.
(g) 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.
(vill) 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.
(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 FR aircraft, then apply a limitation in the rotorcraft flight manual or rotorcraft flight manual supplement limiting IFR coupled RNAV approach operations to a maximum glidepath Page MG 1 -16
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:
(1) 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.
(i) 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.
(1) General. There are installations of avionic equipment and systems 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, there are optional approvals requests for most of these systems not performing any required functions. However, most of the applicants anticipate requesting approval for the system use in the future to perform some required function or to allow required maintenance predication 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 27 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) (ill)(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 Page MG 1 -17
AC 27-1B, Chg 7 2/4/2016 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 system hardware, including airborne electronic hardware, operated under the control of the imbedded software should be shown to comply with § 27.1301. Additionally, in showing compliance to § 27.1309(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, RTCA 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
27.1309 of this AC. Carefully consider the selection of the software level because sometimes the initial system approval basis is on the system being a non-required optional system. Further, if it shows that 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 certified, it is very difficult to qualify software to higher levels of "quality." Because of this, we recommend choosing the software at the level consistent with 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 gaining more experience with the operation of the system, and ultimately planning to seek approval to perform required functions, then initially obtain an appropriate higher level of software.
Note: Consider extensive service experience as a basis for level of criticality without accomplishing RTCA Document DO-178 procedures.
(20) Rotorcraft Health and Usage Monitoring Systems (HUMS).
(i) General. There can be a division of HUMS into two major categories, health monitoring systems and usage monitoring systems. The provisions of § 27.1301 are used to determine that the system performs its intended function. The provisions of § 27.1309(a) and (b) are used to look at the impact of environmental conditions and malfunctions. There are no HUMS approvals to replace service life or other specific physical limits but several systems are now in the process of seeking approval. We consider health monitoring systems the serious applications of this technology, and it will probably be some time before the necessary database to allow full reliance on this technology is available. There have been numerous approvals of usage monitoring systems as optional equipment, and a good example of this technology is a condition Page MG 1 -18
monitoring system described in paragraph b. (19) above. Refer to section AC 27 MG 15 of this AC for guidance on the certification of HUMS.
(ii) Health Monitoring Systems.
(A) We anticipate that these systems will begin as "optional" systems in order to build a data base to support expansion of the approval to achieve credit for extension of maintenance intervals, and so forth. Some of these applications may require system redundancy and some may require level A or equivalent software as defined in RTCA Document DO-178.
(B) Some systems that are under consideration will utilize off aircraft processing of data. If pursuing this, assume that the aircraft data will be lost or misplaced at the processing center, and the aircraft system design should consider this possibility. Some on board data storage is one way to account for this lost data. The integrity of the processing center's software should be equal to that of the aircraft software. In addition, specify the intervals for processing the data from each flight as part of the approval.
(C) Due to the limited experience with these systems, we suggest using the issue paper process to record the progress of the approval, and to provide information for later updating of this guidance material.
Page MG 1 -19
CHAPTER 3
AIRWORTHINESS STANDARDS
NORMAL CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 27 MG 2. STANDARDIZED TEST PROCEDURE FOR ROTORCRAFT DC ELECTRICAL SYSTEM TESTS.
a. Test Requirements.
(1) General. The following functions and characteristics are to be evaluated:
(i) Normal System Operation.
(ii) Parallel Load Division.
(iii) Excitation.
(iv) Stabilization.
(v) Systems Malfunction.
(vi) Environmental Capability.
(vii) Electromagnetic Compatibility.
(viii) Cooling Capability.
(ix) Surge Characteristics, Ripple Voltage, and Voltage Spikes.
(2) Instrumentation. Calibration records should be available for all instrumentation. Enough specific currents and voltages should be recorded to allow reconstruction of any sequence of events that would happen as a result of any system testing described herein.
(3) Regulatory References. Sections 27.1301, 27.1307(c), (d), (e), 27.1309,
27.1351, 27.1353, 27.1357, 27.1361, 27.1365, and 27.1367.
(4) Miscellaneous, The assigned FAA/AUTHORITY systems and equipment engineer normally witnesses these tests and should be notified as far in advance of the testing as possible to minimize scheduling problems. Conformity of the test setup must be established prior to conducting any testing. Most of the above test categories can be conducted on a bench test setup. A bench test setup is especially recommended in the case of the system malfunction test. It is the applicant's option to demonstrate his equipment either on the bench or installed for ground tests. When a bench setup is Page MG 2 - 1