62 must be installed in accordance with this AC and the associated FMS must comply with TSO- C115b (or later revision).
Note 1: Multi-sensor systems may also have incomplete system TSO-C129(AR) Class A or TSO-C146(AR) Class Gamma approvals (see paragraph 3-2.e).
Note 2: TSO-C129a has been cancelled so it is not possible to receive a new incomplete system TSO-C129a TSOA. But equipment with an existing TSO-C129a TSOA may still be produced and installed.
(3) Multi-sensor systems that rely on ground-based NAVAIDS. Multi-sensor systems that require the use of ground-based NAVAIDS, such as DME/DME, can be used to conduct RNP 1 operations provided that the AFM/RFM or AFMS/RFMS shows the aircraft is approved for RNP instrument flight operations, the aircraft meets the functional and performance criteria in this chapter (e.g., RNP performance monitoring and alerting), and the criteria of chapter 6 appropriate to the ground-based NAVAIDS and/or inertial systems used.
Chapter 10. Equipmen t Performance - Baro-VNAV.
10-1. General Limitations for Operations under IFR.
a. A baro-VNAV system may be approved for enroute, terminal, and approach use within the contiguous United States, Alaska, and Hawaii. However, unless compensated for temperature, baro-VNAV equipment can only be used within the limitations for temperature published on approach procedure charts.
b. Systems providing temperature compensation to the baro-VNAV guidance must comply with RTCA/DO-236B, appendix H.2. This enables baro-VNAV operations outside of the temperature limits published on approach procedure charts.
(1) Equipment manufacturers may include compensation for temperatures above and below the limits published on approach charts.
Note: Any equipment limitations must be documented in the installation manual.
(2) Temperature compensation may be provided on segments outside of the final approach segment if the equipment includes a method for the flightcrew to inhibit the compensation function.
Note: Aviation authorities in different countries may or may not authorize temperature compensation outside the final approach segment.
c. Baro-VNAV equipment may also be used to provide advisory vertical guidance to aid in more efficient and precise operation of the aircraft for enroute, terminal, and/or approach operations (see chapter 4). The primary barometric altimeter will be the primary altitude reference for all flight operations.
d. Baro-VNAV performance has not been shown to be adequate for vertical guidance on LPV or GLS approaches.
10-2. Baro-VNAV Equipment Performance for Operations under IFR.
a. The initial certification of a baro-VNAV system requires an engineering evaluation because of the need to v erify performance, failure indications, environmental qualifications, etc.
Subsequent installations of the same baro-VNAV equipment system in other aircraft may require additional engineering evaluation, depending upon the degree of integration with other aircraft systems, in particular autopilot and FD systems.
b. For enroute, terminal, and approach IFR operations, the airborne baro-VNAV system must have TSE components in the vertical direction that are less than those shown in Table 6 below, 99.7 % of the flying time (reference RTCA/DO-236B, paragraph 2.1.2).
Note: GPS/SBAS Class 2 and 3 as well as GPS/GBAS vertical po sitioning performance exceeds the accuracy requirements of a barometric sensor used for final approach VNAV. The GPS/SBAS 50m Vertical Alert Limit (VAL) used for LNAV/VNAV is consistent with baro-VNAV and may also be used to comply with RNP approach.
Altitude Region (MSL) Level Flight Segments & Climb/Descent Intercept of Clearance Altitudes Flight Along Specified Vertical Profile At or below 5000 ft.
150 ft. 160 ft.
5000 ft. to 10000 ft 200 ft. 210 ft.
10000 ft. to 29,000 ft 200 ft. 210 ft.
Above 29,000 ft to 41,000 ft 200 ft.
(See Note 2) 260 ft.
Table 6. Vertical Path Performance Limit for Baro-VNAV
Note 1: These requirements are based upon airborne altimetry and avionics systems that provide performance consistent with reduced vertical separation minimums (RVSM) requirements. Aircraft meeting reduced vertical separation minimums (RVSM) requirements may apply the altimetry system error data developed during the RVSM qualification toward the vertical total system error for the above 29,000 ft to 41,000 ft row in table 6. However, the altimetry system error cannot be extrapolated to the other altitude blocks.
Note 2: For aircraft type designs prior to January 1, 1997, the value is 200 ft. in the cruise flight envelope and is not to exceed 250 ft. over the full aircraft operating envelope.
Basic height-keeping parameters for 1000 ft. vertical separation minimum between flight levels 290 and 410 are in ICAO Document 9574, Manual on Implementation of 1000 ft. Vertical Separation Minimum between FL 290-FL410 Inclusive.
Note 3: Baro-VNAV equipment error includes all errors resulting from the vertical guidance equipment installation.
This includes errors of the altimeter system and along-track or horizontal coupling error.
Note 4: Table 6 does n ot address altitudes above FL 410 because current altimetry and baro-VNAV systems are adequate for the 2,000 ft. air traffic control vertical separation criteria.
c. Flightcrew Inputs.
(1) The altitude associated with the active waypoint should be to the nearest 100 feet for enroute and terminal flight phases, and nearest 10 feet for the approach phase. If provided, waypoint horizontal position should be in increments not greater than 0.1 nautical miles.
(2) The ascent or decent angle should be to at least the nearest 0.1 degree for equipment that specifies gradient angles.
(3) The station elevation, if necessary for equipment employing slant range error correction, should be at least to the nearest 1,000 feet for enroute and terminal flight phases, and to the nearest 100 feet for the approach phase.
(4) For terminal and approach operations, the ability to enter the altitude associated with at least eight (for TO-FROM equipment) or nine (for TO-TO equipment) successive waypoints.
(5) A means to confirm input data correctness prior to the system using the new data.
d. System Displays.
(1) The system displays should give no operationally misleading information.
(2) There should be a continuous display of vertical path deviation with the performance indicated in Table 7 below.
Enroute/Terminal (feet) Approach (feet) Minimum Full-Scale Deflection ≥ 500 ≥ 150 (see note) Readability ≤ 100 ≤ 30 Minimum Discernable Movement ≤ 10 ≤ 5 Table 7. Vertical Path Deviations
Note: Smaller values of minimum full-scale deflection for approach may be acceptable provided the proposed value is found satisfactory by an engineering evaluation.
(3) The vertical guidance presentation should be compatible with the aircraft’s flight instrum entation such that the pilot is continuously furnished the aircraft’s vertical deviation with respect to the pre-programmed ascent/descent or level flight profile.
e. Alert Indications.
Alert indications for the system should be located on or near the vertical path deviation indicator and should provide a readily discernible annunciation to the pilot(s) for any of the following:
(1) Inadequate or invalid navigation signals or sources;
(2) Absence of primary power;
(3) Inadequate or invalid navigation displays or output sources; and
(4) Equipment failures.
Note: These failure/status indications must occur independently of any operator action. Power or navigation equipment failures may be indicated in a common manner.
In the approach mode, the lack of adequate navigation signals or sources will be annunciated by means of a flag displayed on the primary vertical navigation display. In other modes, an appropriately located annunciator may be used.
f. Additional Constraints.
(1) The baro-VNAV equipment should indicate the aircraft vertical path position to the accuracy specified in paragraph 10-2.b within five seconds after any maneuvering or changes in attitude encountered in normal operations.
(2) The system should be capable of providing navigation guidance to the accuracy specified in paragraph 10-2.b within 20 seconds after input of the desired vertical track information (assuming sensor outputs are available).
(3) Navigation guidance should be available within five seconds of waypoint data input.
(4) The equipment should have the capability to meet the criteria outlined in paragraph 10-2 throughout the range of environmental conditions that will be encountered in actual service. Exposing the equipment to the environmental test conditions of TSO-C115b (or later revision) may be used to demonstrate this capability. The environmental test conditions contained in RTCA/DO-160F may be used to demonstrate this ability for baro-VNAV systems certified independent of a multi-sensor RNAV system.
67 Note: Previously certified baro-VNAV systems may have used an earlier RTCA/DO-160 revision. This equipment may still be installed within the provisions of its original certification.
(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 68
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.
a. AC 20-115B Radio Technical Commission for Aeronautics, Inc. Document RTCA/DO-1 78B, defines an acceptable means of qualifying software. In December 2011, RTCA published RTCA/DO-178C, Software Considerations in Airborne Systems and Equipment Certification. The FAA plans to update AC 20-115B to recognize RTCA/DO-178C as an acceptable means of qualifying software, but there currently is no AC or TSO recognition for RTCA/DO-178C. In the interim, applicants may choose to use RTCA/DO-178C instead of RTCA/DO-178B provided they declare their intention to the applicable aircraft certification office for the project. However, doing so will most likely require submitting a deviation request, particularly if a TSO that invokes RTCA/DO-178B is involved.
b. 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.
Note: It may be possible to obtain approval for navigation functions that have hazardous level effects with FMS software developed to DO-178B level C criteria. AC 20- 174, Development of Civil Aircraft and Systems provides an acceptable method for establishing design assurance levels.
This guidance may be helpful for navigation architectures containing independent functions.
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.
Equipm ent 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 separation cannot be achieved, the following questions must 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 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 m ost 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, 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.
11-9. Magnetic Variation Data and Onboard Database.
a. Avionics typically convert true heading references to m agnetic 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 a 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 updated consistent with this cycle.
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 result in placing 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.
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.