(5) The equipment should provide a means for the flightcrew to determine system status prior to flight.
(6) The equipment should provide the navigation accuracy specified in paragraph
10-2.b for all groundspeeds up to a maximum value; and, for all ascent (if applicable) and descent rates up to a maximum value to be set by the applicant.
(7) The equipment should provide a means to alert the flightcrew prior to arrival at a waypoint for anticipating necessary vertical maneuvering. This indicator should be located on or near the vertical path indicator. A procedural means based on a continuous and properly located distance to waypoint display may be used for vertical maneuver anticipation for baro-VNAV equipment that is not coupled to a FD or autopilot.
(a) Systems that provide steering signals for FDs or autopilots should provide automatic vertical maneuver anticipation and a waypoint alert that occurs prior to the initiation of the vertical maneuver. Systems that are coupled to the automatic guidance/control system(s) should not cause the aircraft to depart an assigned altitude until the impending altitude change is indicated to the crew within the pilot’s primary field of view, then acknowledged by timely crew action.
(b) Acceptance of the acknowledgment should not precede the indication if this acknowledgement is stored by the equipment. The acknowledgement timing of an impending vertical path change depends on operational procedures and aircraft/equipment design;
however, past practice has shown that this acknowledgment should not occur more than five minutes prior to the impending vertical path change.
(8) If parallel offset track capability is provided, waypoint alerting and vertical maneuver anticipation should be provided prior to arrival at the point where the offset track intersects the angle bisector of the parent track. These functions should operate as described above in paragraph 10-2.d(7).
(9) The equipment should be capable of providing correct vertical path guidance when interfaced with lateral navigation equipment providing turn anticipation. The baro-VNAV equipment should recognize the angle bisector of the lateral track change as the “zero distance to waypoint” location.
g. The software should be verified and validated to at least level C as defined in RTCA/DO-178B for baro-VNAV equipment that uses a digital computer.
Chapter 11. General Installation Considerations.
11-1. Introduction.
The f ollowing information applies to the installation of all positioning and navigation equipment intended for IFR use.
11-2. Failure Classification.
a. From enroute through Category I precision approach, the loss of navigation function is typically considered to be a major failure condition for the aircraft (see AC
25.1309-1; AC 23.1309-1; AC 27-1; or AC 29-2 as applicable). Other aircraft navigation systems should be considered when determining GNSS loss of navigation, which could be major (no other navigation systems) or minor (other applicable navigation systems).
Navigation data is considered to be misleading when un-annunciated position errors exist. For enroute, terminal, LNAV, and LNAV/VNAV approaches, presenting misleading information to the flight crew is considered to be a major failure condition for the aircraft. For LP/LPV and GNSS Category I approaches, presenting misleading information to the flight crew is considered to be a hazardous failure condition. These failure classifications are summarized in table 8.
Advisory Vertical Guidance Enroute/ Terminal Area/ Nonprecision Approach (LNAV or RNP
0.3) Nonprecision Approach with Vertical Guidance (LNAV/VNAV) LP/LPV Approach GNSS Precision Approach (Cat. I) Loss of Navigation No Effect Major Major Major Major Misleading Information Minor Major Major Hazardous Hazardous Table 8. Typical Hazard Classifications
Note: For RNP values less than 0.3, losing RNP capability constitutes loss of navigation. Refer to appendix 2 for further RNP AR airworthiness information and AC 90-101 (latest revision) for complete guidance on RNP AR operations.
b. The applicant must conduct a safety assessment of the positioning/navigation equipment installation to verify that design errors and failure modes meet the probability requirements for that failure class. AC 23.1309-1, AC 25.1309-1, AC 27-1, or AC 29-2, per the latest revision levels, provide an acceptable means for showing that the hardware complies with pertinent airworthiness requirements. See paragraph 14-2.a for GPS/SBAS and GPS/GBAS retrofit installation guidance related to navigation displays previously approved for ILS.
c. Any probable failure of the positioning/navigation equipment must not degrade or adversely affect the normal operation and performance of other required equipment or create a 63
flight hazard . The interfaces with other aircraft equipment must be designed such that normal or abnormal positioning/navigation equipment operation must not adversely affect the operation of other equipment nor must operation of other equipment adversely affect the positioning/navigation equipment operation.
11-3. Software Considerations.
AC 20-115 (latest revision) Radio Technical Com mission for Aeronautics, Inc.
Document RTCA/DO-178B, defines an acceptable means of qualifying software. The applicant is encouraged to submit the Plan for Software Aspects of Certification (PSAC) early in the software development process. Early submittal will allow timely resolution of issues such as partitioning and determining software levels. Software certification is normally addressed during the design approval for positioning/navigation equipment; but, should be confirmed at installation to ensure the certification level is appropriate for the installation intended function.
11-4. Hardware Considerations.
AC 20-152 (latest revision) RTCA, Inc., Document RTCA/DO- 254, Design Assurance Guidance for Airborne Electronic Hardware, defines an acceptable means of qualifying complex electronic hardware devices. The applicant is encouraged to submit the Plan for Hardware Aspects of Certification (PHAC) early in the development process. Hardware certification is normally addressed during the design approval for positioning/navigation equipment; but, should be confirmed at installation to ensure the certification level is appropriate for the installation intended function.
11-5. Installed Equipment Compatibility.
There is no one, single, standard ized interface for positioning and navigation equipment to other equipment on-board the aircraft such as displays, autopilots, terrain warning, etc.
Positioning and navigation equipment manufacturer’s installation manuals/instructions should define what other equipment is compatible with the positioning and navigation system.
Equipment manufacturers are encouraged to develop compatible equipment lists and/or detailed interface requirements for their installation manuals/instructions. The installer must ensure that other on-board equipment interfaced with the positioning and navigation systems is compatible;
and, the airworthiness approval holder is ultimately responsible for defining the installation.
But the installation burden is greatly eased when equipment manufacturers define compatible systems in their installation manual/instructions, including software version and/or part number if necessary.
11-6. Installation Instructions.
a. The equipment m ust be installed in accordance with the instructions and limitations provided by the positioning and navigation equipment manufacturer. The airworthiness approval will address any additional installation specifics.
b. Equipment should be installed with separation between wires of redundant equipment (see AC 43.13-1 latest revision). Wire separation will mitigate the possibility of loss of navigation due to a single event. During installation approval of the system, when wire 64
separation cannot be achieved, the following questions m ust be evaluated and the potential for single event upsets minimized:
(1) Is it possible for a cable harness to be exposed to wire chafing in a manner that both channels fail simultaneously?
(2) Is the cable harness located near flight control cables, high electrical capacity lines or fuel lines?
(3) Is the cable harness located in a protected area of the aircraft (isolated from engine rotor burst)?
(4) Is any electromagnetic interference (EMI) between systems caused by cable routing?
11-7. Environmental Considerations.
a. Most equip ment will have been tested by the equipment manufacturer to the environmental categories described in RTCA/DO-160 (applicable revision), with results described in an environmental qualification form. The airworthiness approval applicant must ensure the environmental categories (or criteria) to which the equipment has been tested are compatible with the aircraft environment in which the positioning and navigation equipment is installed. See AC 21-16F (or later revision) RTCA Document DO-160 versions D, E, and F, Environmental Conditions and Test Procedures for Airborne Equipment, for guidance on differences among RTCA/DO-160 versions D, E, and F.
b. For equipment that has not been tested to the environmental categories described in RTCA/DO-160 (applicable revision), either the equipment manufacturer or airworthiness applicant must thoroughly define the intended aircraft environment and conduct comparable normal and abnormal environment testing.
11-8. General Human Factors Considerations.
a. Control Accessibility.
(1) Controls installed for in-flight operation should be readily accessible from the flight crew’s seated position. Only single-hand operation should be required, the controls should be readily identifiable, and the use of controls should not obscure pertinent displays.
(2) The equipment should be designed so that controls intended for use during flight cannot be operated in any position, com bination, or sequence that would result in a condition detrimental to the operation of the aircraft or the reliability of the equipment.
(3) Controls should provide feedback (e.g., tactile, visual) when operated.
(4) Control operating force should be appropriate for its intended function.
Note: Low forces m ight provide insufficient feedback, while high forces might impede intentional rapid use.
(5) Controls should be resistant to inadvertent activation. Common and acceptable means of reducing the likelihood of inadvertent operation through design include the following:
(a) Placing fences between closely spaced adjacent controls.
(b) Concave upper surface of keys to reduce slippage.
(c) Size of control surface sufficient to provide for accurate selection.
(d) Placing guards over controls.
(e) Providing appropriate sensory feedback, or explicit confirmation of activation.
(6) The function for each control should be indicated, unless obvious. Pilots should be able to quickly and accurately determine the function of the control with minimal experience or training. If a control can be used for multiple functions, the current and inactive functions should be distinguishable.
(7) Controls/input devices should be organized according to the following principles, when feasible:
(a) Controls should be organized in logical groups according to function and frequency of use.
(b) Controls should be easily associated with the related elements (e.g., displays and labels) that identify their function. For example, line select function keys should align with adjacent text.
(c) Controls used most frequently should be the most accessible.
(d) Dedicated controls should be used for frequently used functions.
(e) Line select function keys should align with adjacent text.
(8) Use of two or more controls simultaneously (e.g., pushing two buttons at once) in flight should not be required to perform a function.
(9) Controls that do not require adjustment by the flight crew (e.g., maintenance functions) should not be readily accessible to the flight crew.
(10) Controls and their labels should be identifiable during all normally expected ambient light conditions, including direct sunlight and nighttime.
(11) Control identifiers and other information should not be obstructed by the control input devices.
b. Display Visibility.
(1) Each display element, used as a primary flight instrument in the guidance and control of the aircraft, should be located where it is clearly visible to the pilot with the least practicable deviation from the pilot’s normal position and line of vision when looking forward along the flight path.
Note 1: CDI displays contained in the Control Display Unit (CDU) will most likely not be acceptable for IFR operations.
Note 2: FTE can be reduced when numeric display information is integrated with the non-numeric display or is located within the pilot’s primary field of view. Both digital cross-track and track angle error have been shown to reduce FTE. This information should be displayed together (either within the CDU or remotely displayed near the non-numeric display) for better tracking performance.
Using non-numeric cross track data integrated with nonnumeric track angle error data into one display may provide the optimum situation and control information for the best overall tracking performance.
(2) The appropriate flight crew member(s) should have an unobstructed view of displayed data when in the seated position.
(3) Connection to external displays (CDI, HSI, moving map, annunciator panel, etc.) should be consistent with the equipment installation instructions.
(4) The horizontal (and vertical) deviation(s), display(s), and failure annunciations should be located within the pilot's primary field of view, as should any indication requiring immediate aircrew action.
(5) Compliance with limitations in the equipment installation instructions for display readability should be verified.
c. Lighting Conditions.
(1) All displays, controls, and annunciators must be easily readable under all normal cockpit conditions and expected ambient light conditions (total darkness to bright, reflected sunlight).
(2) Night lighting provisions must be compatible with other cockpit lighting;
particularly if night vision goggle compatibility is desired.
Chapter 12. General In stallation Considerations - Antennas.
12-1. Antenna placement.
Paragraphs (a) through (f) below are specific to GNSS antennas.
a. Typically, a GNSS antenna is lo cated forward or aft of the wings on the top of the fuselage.
b. GNSS antennas must be installed to provide the widest, unobstructed field of view to the satellites. The antenna installation instructions should provide information on how to determine a location that minimizes the potential for signal blockage by any portion of the aircraft. Shadowing by aircraft structure (and in some cases by rotorcraft blades) can adversely affect the operation of the GNSS equipment.
c. The antenna placement on the airframe should be optimized to ensure the receiver can take full advantage of a 5 degree mask angle (or lower if the receiver installation instructions identify the equipment is certified to a lower mask angle). This includes consideration of antenna location with respect to blockage from airframe components, airframe structures, engine components, or other antennas with the aircraft at typical level cruising attitude. The antenna should also be located to minimize the effects of aircraft shadowing during typical maneuvers.
d. The antenna should be separated as much as practical from transmitting antennas
(e.g., VHF and high frequency radio, satellite communications (SATCOM), DME, direction finder, emergency locator transmitter, and traffic and collision alerting system). For small aircraft, the antenna should also be separated as much as practical from the windscreen to prevent case-to-antenna coupling.
e. The VDB antenna should be installed so that the maximum received power from any on-board transmitter does not exceed the desensitization levels of the VDB receiver specified in RTCA/DO-253C, paragraph 2.2.9.1.
f. The GNSS multi-path error model specified in RTCA/DO-229D and RTCA/DO-253C was developed and validated using flight test data collected on a variety of large, fixed-wing aircraft. Further validation was done using computer modeling of large, fixed-wing aircraft. For installations on rotorcraft, antenna location should consider the compatibility of the resulting multi-path errors with this model. This may require additional equipment functional flight evaluation or analytical evaluation to confirm the antenna location is suitable.
g. For installations on rotorcraft, the effects of the rotor blades on antenna performance should be considered. This may require additional equipment functional flight evaluation or analytical evaluation to confirm the antenna location is suitable.
h. For multiple-sensor installations, the installer should reduce the likelihood that a single lightning strike affects all the sensors (i.e., do not place them in a straight line from the front to the rear of the fuselage).
12-2. Anti-Ice Protection.
If the aircraf t is approved for flight into known icing conditions, the antenna must not be susceptible to ice buildup (i.e., is installed in a non-icing location on the aircraft, or is of a sufficiently low profile that ice does not accumulate on the antenna). Alternatively, the equipment can be shown to operate satisfactorily when the antenna is subject to icing if there are no harmful effects of the ice build-up, such as possibly ingesting accumulated ice into the engine or degradation in aerodynamic performance. The effects of ice accumulation on the antenna, if any, can be found in the equipment manufacturer's installation manual/instructions.
See the latest revisions of ACs 23.1419-2 and AC 25.1419-1 for additional fixed-wing aircraft guidance. For additional rotorcraft guidance, AC 27.1419 is contained in the latest revision of AC 27-1 and AC 29.1419 is contained in the latest revision of AC 29-2.
12-3. Antenna Cables.
Double shielded cables should be used to prevent interference coupling into the cable.
12-4. Structure.
Any m odifications to the aircraft to install a new antenna need to be evaluated as part of the airworthiness approval for their impact on aircraft structure. Examples are evaluating and testing antenna installations for buffet and vibration (compliance with 14 CFR part XX.251), or, when modifying pressurized structures (compliance with 14 CFR part XX.841 and XX.843).
For specific guidance relating to modifications in the fuselage structure, see AC 43.13-2 (latest revision). Additional guidance information related to structures can be found in the latest revisions of ACs 20-107, 23-13, and 25.1529-1.
Chapter 13. General In stallation Considerations - Sensors.
13-1. Introduction.
This chapter provides guidance related to positioning/navigation sensor installation. T his chapter also applies to stand-alone navigation equipment installation, since that equipment has an embedded sensor. This guidance applies to all installations, but is only expected to be specifically evaluated as part of the initial airworthiness approval (i.e., initial airworthiness approval may provide sufficient substantiation for follow-on installations).
13-2. Positioning and Navigation Configuration Strapping.
Often, positioning and navigation equipm ent uses software configuration straps or installation set parameters entered either manually by the installer or by using an aircraft personality module. These software configuration straps or parameters disable/enable functionality; configure the input/output formats; determine the displayed units of measure; etc.
The software configuration programming documentation must become a part of the installation package and should be included in the master drawing list. When using an STC-AML (see paragraph 2-3), approved multiple configurations may be specified.
13-3. Navigation Source Selection.
a. For insta llations where positioning and navigation outputs can drive a display that is shared with other navigation equipment (e.g., VOR/DME, ILS, GPS/SBAS, baro-VNAV), the pilot must be able to select the source of guidance, and the selected source must be clearly annunciated to the flightcrew on or near the affected display.
b. There are many possible navigation source and service level combinations and permutations given the variety of sensors and capabilities that can be integrated into the aircraft.
Some of the capabilities are very similar, but have subtle differences that are very significant.
The aircrew must have a clear, unambiguous annunciation of what capability is being provided by the navigation system. This can either be accomplished by multiple annunciation indicators, or by removing some navigation capabilities when others are added to reduce the annunciator complexity.
c. GNSS-based navigation (GPS, GPS/SBAS, GPS/GBAS) might not require differentiation unless integration complexity requires it for clear, unambiguous indication of selected capability to the flightcrew. For example, oceanic, enroute, or terminal RNAV modes or LNAV-only approach capability may not require differentiation.
d. When applicable, annunciation of the selected source should be driven by the same relay switch to preclude erroneous information in case of switch failure.
e. Autopilot navigation modes related to the navigation source should be inhibited if the displayed source is not the same as the source driving the autopilot. This is particularly critical for approach operations (i.e., autopilot in approach mode). One possible method is to consider integrations that do not permit separate display source and autopilot source navigation 70
selection.
f. Navigation source annunciations included in the optim um primary field of view do not also have to be shown on a heads-up display.
13-4. Dual Positioning and Navigation Installation s.
a. Paragraph 13-4 describes guidelines for synchronizing dual positioning and navigation equipment installations. Synchronization refers to the ability for control inputs to one positioning and navigation equipment set to automatically update the other equipment set.
Dual installations should be synchronized whenever possible to reduce crew workload and prevent confusion over which system/flight plan is driving the navigation data. If the functional hazard assessment requires dual positioning and navigation equipment or is operationally required, then synchronization is required.
b. If the navigation equipment is not synchronized, then the following issues should be evaluated:
(1) The pilot and co-pilot (if applicable) should be able to view and enter data in the offside equipment. This must not interfere with throttle levers, flap handle, etc.
(2) The workload associated with manually updating both equipment sets to maintain consistency between them should not be too burdensome.
(3) There should be no possible confusion as to which equipment is driving the autopilot and navigation displays.
(4) Controls, displays and annunciations must not result in misleading information, pilot confusion or unacceptable workload due to possible inconsistencies from differences in the equipment (e.g., different flight plans making one unit go into approach mode while the other does not). Evaluations for these types of inconsistencies are of particular concern when the cockpit architecture enables cross coupling (e.g., GNSS-2 switched to drive side 1 displays).
13-5. Intermixing RNAV equipment.
a. Where m ultiple RNAV systems are intended to be used simultaneously (typically in two-pilot aircraft), installing area navigation equipment with different crew interfaces can be very confusing and could lead to problems since they may have conflicting methods of operation and conflicting display formats. There can be problems even when intermixing different versions of the same equipment.
b. At a minimum, consideration should be given to the following potential incompatibilities, particularly when the cockpit architecture allows for cross coupling (e.g., RNAV-2 switched to drive side 1 displays):
(1) Data entry.
The two units m ust have consistent methods of data entry and similar pilot procedures for accomplishing common tasks. Workload should be acceptable, and it should be easy for pilots to identify and recover from data entry mistakes.
(2) CDI scaling.
CDI scaling sensitivity must be consistent across different equipment or labeled.
(3) Display symbology and mode annunciations.
There must be no conflicting symbols or annunciations (e.g., a common symbol used for two different purposes), and differences should be specifically highlighted during the evaluation for any potential confusion they may cause.
(4) Mode logic.
The modes internal to the equipment and interfaced to the rest of the aircraft should be consistent across RNAV units.
(5) Equipment failure.
The effect of failure of one RNAV unit must not result in misleading information or failures in the other unit.
(6) Displayed data.
The display of primary navigation parameters must use consistent units and a consistent notation across multiple RNAV units. Industry standard labels and nomenclature should be used.
(7) Database differences.
Intermixed RNAV units must use the same navigation database to prevent conflicting information among the equipment.
13-6. Interface to FGS.
a. Paragraph 13-6 describes guidelines for interfacing the positioning and navigation equipm ent with a FGS. When used in paragraph 13-6, the word “consistent” means the installation does not alter the positioning and navigation equipment’s intended function, nor does it alter the cockpit design philosophy.
b. Connection to the autopilot must be consistent with the autopilot installation instructions and the positioning and navigation installation instructions. The positioning and navigation system manufacturer should provide instructions on connection with specific 72
autopilots to which they have shown compatibility.
c. Operational compatibility should be verified between the positioning and navigation equipment and the FGS. Protection should exist in the positioning and navigation equipment or the FGS to keep the aircraft within the approved operational envelope (e.g., roll, pitch, speed, and altitude). See the relevant guidelines for the particular aircraft (e.g., the latest revision of AC 23-17, AC 25.1329-1, AC 27.1329 contained in AC 27-1, and AC 29.1329 contained in AC 29-2).
d. A continuous and unambiguous indication must be provided of the FGS modes actually in operation, as well as those that are armed for engagement. This includes a clear indication whenever the mode has been armed either manually by the flight crew, or automatically by the system.
e. The positioning and navigation equipment must be compatible with the FGS modes of operation. For example, the arm, engage, and disengage sequence of the positioning and navigation equipment should be consistent in the annunciation and engage/disengage timing of the FGS. This is particularly important during GPS/SBAS-augmented GNSS approaches that include different levels of service.
f. If the positioning and navigation equipment is connected to a reduced bank selector, the equipment bank angle, like the FGS, must not be limited by this switch selection during approach. Consistency in the operation must be maintained.
g. Some aircraft operate in areas of the operational flight envelope where buffet onset can occur when normal maneuvering load factors are present (e.g., at higher altitudes). This is a concern since the positioning and navigation equipment can automatically sequence waypoints and initiate turn maneuvers that may or may not have the pilot’s attention. If buffet protection is not automatically provided in the positioning and navigation equipment or FGS
(e.g., bank angle limiting, or cruise altitude limiting based upon buffet margin), an AFMS/RFMS limitation should be added to the performance section, prohibiting cruise operation at weight/altitude combinations that result in buffet margins less than 1.4g.
h. For those aircraft that have incorporated bank angle limiting, consideration should be given to whether the positioning and navigation equipment is defining a path that cannot be flown or does not conform to the published procedure.
i. If the aircraft includes a synthetic vision system (SVS) or enhanced vision system (EVS) displaying flight guidance, the positioning and navigation input should meet the performance criteria in this AC, as appropriate, to meet the SVS or EVS intended function.
13-7. Interface to Magnetic/True Switch.
If a magnetic/true heading reference switch is installed in the aircraft, the positioning and navigation equipment should be driven by the same switch to maintain consistency in the displays and operation for both manual and automatic heading reference changes. Magnetic heading is the primary heading reference.