fixes on or below the VNAV path to provide an opportunity for a continuous descent final approach to the landing runway. However, for any approach other than LNAV/VNAV, LPV, or ILS there is no guarantee the VNAV path guidance will always clear the final approach segment step-down fix altitude restriction(s). Therefore, airworthiness applicants must include language for a limitation in the AFM(S)/RFM(S) (or equivalent documentation) requiring the flight crew to use the primary barometric altimeter to comply with a final approach segment step-down fix altitude restriction during an LNAV, LP, or non-ILS conventional approach.
Equipment manufacturers should also include a limitation in the equipment operating instructions or flight crew operating manual.
Note 1: The intent of paragraph 12-8.d is to ensure the flight crew does not rely solely on the advisory VNAV guidance deviations for compliance with a step-down fix altitude restriction. The limitation must make it clear that it is unacceptable to follow VNAV path guidance below a step-down fix altitude restriction.
Note 2: Baro-VNAV systems certified before 11/20/1989 may have been certified to a lesser standard that is not consistent with a major failure condition. Operators of these aircraft should apply the final approach segment step-down fix to the LNAV/VNAV line of minima and should use the primary barometric altimeter to ensure meeting the step-down fix altitude constraint.
12-9. Magnetic Variation Data and Onboard Database.
a. Avionics typically convert true heading references to magnetic heading references by using worldwide magnetic variation data contained in an on-board magnetic variation database and a set of software algorithms. The algorithms convert the data into a specific magnetic heading reference for a specific geographic reference point. However, since the Earth’s magnetic fields constantly change, magnetic variation databases need periodic updates to provide accurate magnetic heading references. The National Oceanic and Atmospheric Administration (NOAA) offers the World Magnetic Model, available at http://www.ngdc.noaa.gov/geomag/geomag.shtml, and this product is an acceptable source for updating an aircraft magnetic variation database. NOAA updates the model on a five-year cycle, and magnetic variation databases should be re-assessed consistent with this cycle to make sure they continue to meet their stated performance.
Note: If the magnetic variation database is not kept current, the navigation systems no longer support their intended functions for use during flights conducted under IFR. Failure to maintain and update the magnetic variation database can result in presentation of misleading magnetic heading references that can place the aircraft outside the terrain and obstacle protection provided in instrument procedure and route designs.
b. Equipment design approval holders should identify any operating limitations in their equipment associated with application of the magnetic variation data (e.g., operations using magnetic heading references may only be valid between 82° north latitude and 82° south latitude) to ensure accurate magnetic heading references are presented and used in the aircraft.
Since the earth’s magnetic field is not static, equipment design approval holders should periodically re-evaluate their performance claims. Appropriate evaluation periods will depend on operating limitations, performance expected, and avionics intended function. The equipment design approval holders should also define a continuing airworthiness requirement to update the magnetic variation database and, if applicable, conversion algorithms or hardware when the periodic updates become available. This requirement should also define the maintenance procedures necessary to update the on-board magnetic variation database for their avionics.
12-10. Environmental Considerations.
a. Most equipment 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.
12-11. 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, combination, 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 might 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 (i.e., within the primary optimum field of view).
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.
Note 3: The General Aviation Manufacturers Association with FAA collaboration published Publication Number 10 that has recommended guidelines for Part 23 cockpit/flight deck design. Applicants may apply these guidelines for their Part 23 installations. Additional guidance can be found in FAA Human Factors Design Guide.
DOT/FAA/CT-96/1.
(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, horizontal situation indicator (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.
12-12. Path Definition and Collocated Navigation Aids.
a. ICAO SARPS in Annex 10 permits definition of geographically separated VOR and DME conventional navigation facilities as “collocated” when terminal approach procedures use the facilities and the separation between the facilities’ antennas is no more than 260 feet (80 meters). For other operations, such as en route operations, the SARPS define the facilities as collocated when the separation between the VOR and DME antennas does not exceed 2,000 feet (600 meters). The U.S. identifies these collocated facilities as a “VOR/DME” or “VORTAC” (when the facilities include a tactical air navigation (TACAN) system), and the facilities will share a common 3-letter alphanumeric identifier. For example, despite th e VOR and TACAN antennas being geographically separated by nearly 300 feet, the U.S. considers the Battle Ground VORTAC in Oregon a collocated facility with “BTG” as the three-letter identifier for both the VOR and TACAN.
b. RNAV and RNP routes and terminal procedures, including RNP approach procedures, may use a collocated conventional navigation aid, such as a VOR/DME or a VORTAC, as a waypoint in their path definition. When this occurs, the navigation system must use the location the State provides in the route or terminal procedure path definition for the waypoint’s location in the onboard navigation database. This will ensure the navigation system provides the correct path definition for the aircraft. Failure to use the procedural definition for the waypoint can create misleading guidance for the flight crew.
c. Some multi-sensor navigation systems also use DME facilities as aids in creating a filtered position solution for both RNAV and RNP operations. Other navigation systems use DME-DME positioning when GNSS is lost or unavailable. When using DME facilities to create a position solution for an RNAV or RNP route or procedure, and the route or procedure uses a collocated navigation aid as a waypoint, the navigation system must not use the DME’s latitude/longitude as the default position of the collocated navigation aid. The onboard navigation database definition for the waypoint and the navigation system’s path definition must both match the State’s route or procedure definition.
d. FAA AC 90-108 (latest revision), Use of Suitable Area Navigation (RNAV) Systems on Conventional Routes and Procedures, permits flight crews to use some RNAV systems to overfly routes and terminal procedures defined by conventional navigation aids. The AC also permits some RNAV systems to substitute for a conventional navigation aid when the facility is out-of-service. When the RNAV system overflies a conventional route or procedure, or when the RNAV system substitutes an RNAV position solution for the location of an out-of-service conventional navigation facility, the path definition the RNAV system uses and extracts from the onboard navigation database must match the State’s definition of the conventional route or 102
procedure. For example, when a collocated VOR/DME facility is part of a conventional route or procedure, and the procedural path definition overflies the collocated facility, the RNAV system must use the VOR’s location (i.e. the VOR’s latitude and longitude) in the path definition.
12-13. Runway Position Monitoring.
RTCA/DO-283B, implemented by TSO-C115d, has an option for including a runway position monitoring function in section 2.2.1.4.14. If this option has not been implemented within the FMS installed on transport category airplanes, the FAA recommends implementing the function on the airplane through another on-board system or combination of systems. The intent is to provide a function that detects a discrepancy between the aircraft position/orientation and the runway entered into the positioning/navigation system for departure. When the discrepancy is detected an alert must be annunciated to the flight crew.
Chapter 13. General Installation Considerations - Antennas.
13-1. Antenna Placement.
13-1.1 GNSS-Specific Considerations.
a. Typically, a GNSS antenna is located forward or aft of the wings on the top of the fuselage. 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. Consideration should be given to the following items when choosing an antenna location on the aircraft.
(1) The GNSS 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).
(2) Shadowing by aircraft structure (and in some cases by rotorcraft blades) can adversely affect the operation of the GNSS equipment. Antenna location should minimize blockage from airframe components, airframe structures, engine components, or other antennas with the aircraft at typical level cruising attitude.
(3) The antenna should also be located to minimize the effects of aircraft shadowing during typical maneuvers.
(4) Avoid locations that could subject the antenna to engine exhaust contamination.
(5) Antenna shadowing and engine exhaust can present unique problems on rotorcraft. One possible ground-based method to aid in selecting an optimum location is to temporarily attach the antenna at various places and compare the signal strength. If using this method, it is important to perform the check with the rotors turning since they can be a source of shadowing. But, this method does not remove the need to do functional flight checks to ensure the antenna location is suitable (see paragraphs 13-1.1.c and 13-1.2.a).
(6) It is desirable to minimize the cable length between the antenna and receiver to reduce signal loss. In general, a shorter cable length improves signal strength to the GNSS receiver.
(7) Attempt to place the antenna on the aircraft’s centerline (i.e., symmetrically on the airframe). This is particularly important on metal aircraft as symmetry can potentially affect antenna gain patterns.
b. 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.
c. 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.
13-1.2 General Considerations.
a. In general, the effects of the rotor blades on antenna performance should be considered for any antenna installations on rotorcraft. This may require additional equipment functional flight evaluation or analytical evaluation to confirm the antenna location is suitable.
b. 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).
13-2. Anti-Ice Protection.
If the aircraft 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 instructions/ manual.
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.
13-3. Antenna Cables.
Double shielded cables should be used to prevent interference coupling into the cable.
GNSS equipment manufacturers should indicate the type of cable to use in their installation instructions/manual to minimize insertion losses that could result in reduced performance.
GNSS installations should use the equipment manufacturer-specified cable. However, if the equipment manufacturer did not specify a particular cable, the installation should use high quality coax and connectors because of the high frequency signals and sensitivity to cable losses.
13-4. Structure.
Any modifications 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 105
revision). Additional guidance information related to structures can be found in the latest revisions of ACs 20-107, 23-13, and 25.1529-1.
13-5. Additional Guidance.
Further information on antenna installation considerations, and good avionics installation practices in general, can be found in AC 43.13-1 (latest revision), Acceptable Methods, Techniques and Practices – Aircraft Inspection and Repair and AC 43.13-2 (latest revision), Acceptable Methods, Techniques and Practices – Aircraft Alterations.
-- Chapter 14. General Installation Considerations - Sensors.
14-1. Introduction.
This chapter provides guidance related to positioning/navigation sensor installation. This 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).
14-2. Positioning and Navigation Configuration Strapping.
Often, positioning and navigation equipment 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.
14-3. Navigat ion Source Selection.
a. For installations 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 flight crew 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 flight crew. 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 107
selection.
f. Navigation source annunciations included in the optimum primary field of view do not also have to be shown on a heads-up display.
14-4. Dual Positioning and Navigation Installations.
a. Paragraph 14-4 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 pilot workload associated with manually updating both equipment sets to maintain consistency between the equipment sets.
(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).
14-5. Intermixing RNAV equipment.
a. Where multiple 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 must 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.
14-6. Interface to FGS.
a. Paragraph 14-6 describes guidelines for interfacing the positioning and navigation equipment with a FGS. When used in paragraph 14-6, 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 autopilots to which they have shown compatibility. Interfacing digital positioning and 109