(c) The lateral deviation display must be automatically slaved to the RNP computed path and must have a full-scale deflection suitable for the current phase of flight. It is recommended that the course selector of the deviation display be automatically slewed to the RNP computed path.
Note: This does not apply for installations where an electronic map display contains a graphical display of the flight path and path deviation.
(3) As an alternate means, a navigation map display may be used. The navigation map display must give equivalent functionality to a lateral deviation display with appropriate map scales (scaling may be set manually by the pilot). To be approved as an alternative means, the navigation map display must be shown to meet the TSE criteria and be located in the primary field of view.
(4) It is not necessary for navigation displays, particularly primary flight displays, to include an actual navigation performance (ANP) or RNP accuracy value. The displays only need to provide an alert if the RNP for the operation cannot be met.
g. System Capabilities.
The following are the minimum system capabilities needed in RNP 4.0 equipment:
(1) The capability to continuously display to the pilot flying, on the primary flight instruments for navigation of the aircraft (primary navigation display), the RNP computed desired path and aircraft position relative to the path. For operations where the required minimum flight crew is two pilots, a means for the pilot not flying must also be provided to verify the desired path and the aircraft position relative to the path.
(2) A navigation database, containing current navigation data officially promulgated for civil aviation, which can be updated in accordance with the AIRAC cycle. The stored resolution of the data must be sufficient to achieve the required track keeping accuracy.
The database must be protected against pilot modification of the stored data.
(3) The means to display the validity period of the navigation data to the pilot.
(4) The means to retrieve and display data stored in the navigation database relating to individual waypoints and navigation aids, so the pilot can verify the route to be flown.
(5) A means for the crew to create, review, and activate a flight plan. The system must incorporate a means for the crew to verify flight plan entries or changes before they are activated. The guidance output must not be affected until the flight plan or flight plan changes are activated.
(6) The capability to automatically sequence fixes.
(7) The means to display the following items, either in the pilot’s primary field of view, or on a readily accessible display page:
(a) The active navigation sensor type;
(b) The identification of the active (To) waypoint;
(c) The ground speed or time to the active (To) waypoint; and
(d) The distance and bearing to the active (To) waypoint.
(8) The capability to execute a “Direct to” function.
(9) The capability for automatic leg sequencing with display to the pilots.
(10) The system must have the capability to automatically execute leg transitions and maintain tracks consistent with the following ARINC 424 path terminators:
(a) Course to fix (CF);
(b) Direct to fix (DF); and
(c) Track to fix (TF).
Note: Path terminators are defined in ARINC Specification 424, and their application is described in more detail in RTCA documents DO-236C Chg 1, DO 283B and DO-201A.
(11) The capability to display an indication of the RNP system failure in the pilot’s primary field of view.
(12) The capability to indicate to the crew when the NSE alert limit is exceeded
(i.e., the alert provided by the “onboard performance monitoring and alerting function”).
(13) The capability to fly parallel tracks at a selected offset distance. When executing a parallel offset, the navigation accuracy and all performance criteria of the original route in the active flight plan must be applicable to the offset route.
(a) The system must provide for entry of offset distances in increments of 1 NM, left or right of course. The system must be capable of offsets of at least 20 NM.
(b) System offset mode operation must be clearly indicated to the pilot. When in offset mode, the system must provide reference parameters (e.g. cross-track deviation, distance-to-go, time-to-go) relative to the offset path and offset reference points.
(c) An offset must not be propagated through route discontinuities, unreasonable path geometries, or beyond the ÍAF.
(d) The system must annunciation prior to the end of the offset path, with sufficient time to return to the original path.
(e) Once a parallel offset is activated, the offset must remain active for all flight plan route segments until removed automatically, until the pilot enters a direct-to routing, or until pilot (manual) cancellation.
(f) The parallel offset function must be available for en-route TF and the geodesic portion of DF leg types.
Note 1: Systems compliant with parallel offset requirements in RTCA/DO-236B (or later revision) and RTCA/DO-283A (or later revision) meet the parallel offset criteria for RNP 4.0.
Note 2: RTCA/DO-236C and RTCA/DO-283B require increments of 0.1 nm to support parallel offsets in terminal areas. Using these smaller increments is also acceptable for RNP 4.0 operations.
(14) The system must have the capability to perform fly-by transitions.
(a) Fly-by transitions must be the default when a transition type is not specified.
(b) Navigation systems should be designed to keep aircraft within the theoretical transition area.
(c) Fly-by theoretical transition areas are based upon the following assumptions:
• Course changes do not exceed 120 degrees for low altitude transitions (aircraft barometric altitude is less than FL 195); and,
• Course changes do not exceed 70 degrees for high altitude transitions (aircraft barometric altitude is equal to or greater than FL 195).
Note: Systems compliant with the fly-by transition requirements in RTCA/DO-236B (or later revision), RTCA/DO-283A (or later revision) and RTCA/DO-229C (or later revision) meet the fly-by transition criteria for RNP 4.0.
10-3.2 System Eligibility and Approval for RNP 4.0 Operations.
There are two methods to recognize aircraft and system eligibility for RNP 4.0 operations:
1) RNP certification; and, 2) prior navigation system certification. In both cases, the aircraft must be equipped with at least two independent and serviceable long-range navigation systems;
at least one of which must be GNSS.
a. RNP Certification.
RNP certification is typically documented in the AFM(S) for aircraft that have been formally certificated and approved for RNP operations and typically is not limited to RNP 4.0.
The AFM(S) addresses RNP levels that have been demonstrated to meet the certification criteria and any related provisions applicable to their use (e.g., navigation aid sensor requirements). Operational approval is based upon the performance stated in the AFM(S). This method also applies in cases where certification is received through an STC issued to retrofit equipment, such as GNSS receivers, to enable the aircraft to meet RNP 4.0 performance criteria in oceanic and remote area airspace.
b. Prior Navigation System Certification.
(1) This method is used to approve aircraft whose level of performance under previous standards equates to the RNP 4.0 criteria listed in this AC. The AFM(S) must indicate the aircraft is equipped with GNSS approved as a long-range navigation system for oceanic and remote airspace operations.
(2) RNP 4.0 operations using only GNSS is based upon a pre-departure FDE availability prediction program. 25 minutes is the maximum allowable time for which FDE capability is projected to be unavailable on any one event. This maximum outage time must be included as a condition of the RNP 4.0 operational approval. If predictions indicate that the maximum allowable FDE outage will be exceeded, the operation must be rescheduled to a time when FDE is available.
Note: The FAA’s SAPT prediction program does not provide FDE predictions for oceanic operations.
(a) Aircraft with TSO-C129(AR) equipment must also document the equipment is approval for oceanic operations according to appendix 1 in this AC.
(b) TSO-C115b (or later revision) is acceptable for multi-sensor systems incorporating GNSS sensors.
(3) Multi-sensor systems incorporating an approved INS/IRU can extend the maximum FDE unavailability time based upon the amount of time the system can maintain RNP 4.0 coasting performance without a position update. The approval must indicate the maximum GNSS FDE unavailability time.
Chapter 11. Equipment Performance - Baro-VNAV.
11-1. General Limitations for Operations under IFR.
a. A baro-VNAV system may be approved for enroute, terminal, and approach use within the contiguous U.S., Alaska, and Hawaii. VNAV equipment may be used to provide advisory vertical path guidance to aid in more efficient and precise operation of the aircraft.
However, unless compensated for temperature, baro-VNAV equipment can only be used within the limitations for temperature published on approach procedure charts. The barometric altimeter must always be the primary altitude reference for all flight operations (see paragraphs 12-7, 18-2.b and 23-3.1).
b. Systems providing automatic temperature compensation to the baro-VNAV guidance must comply with RTCA/DO-283B, appendix H. 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 other than the final approach and missed approach (i.e., the segments prescribed by RTCA/DO-283B, appendix H) if the equipment includes a method for the flight crew to inhibit the compensation function.
Equipment manufacturers providing baro-VNAV temperature compensation on other segments must specify language in the installation instructions/manual for an AFM(S)/RFM(S) caution that the flight crew/pilot must coordinate use of temperature compensation with ATC prior to employing this function. The reason for an AFM(S)/RFM(S) caution is to ensure there is no loss of separation between an aircraft employing temperature compensation and an aircraft not employing this function.
Note: Aviation authorities in different countries may or may not authorize temperature compensation outside the final approach segment.
c. Procedures for manual altitude corrections must be established for systems that do not provide automatic temperature compensation. A pilot workload evaluation must be performed for all segments in the approach, including the missed approach holding waypoint.
d. 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.
e. Baro-VNAV performance is not adequate for vertical guidance on LPV or GLS approaches.
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11-2. 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 verify 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-283B, paragraph 2.2.2.6.1).
Misleading guidance during LNAV/VNAV approach operations is considered a major failure condition (see Table 8). A baro-VNAV system providing vertical guidance during the final approach segment of an LNAV/VNAV approach operation must meet the design error and failure mode probability requirements that satisfy a major failure condition (see paragraph 12-2).
Note 1: Baro-VNAV vertical guidance is independent from the lateral guidance. Loss of baro -VNAV guidance during an LNAV/VNAV approach results in a fail-down to LNAV or a missed approach. Therefore, loss of navigation for baro-VNAV is considered a minor failure condition.
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.
(1) Baro-VNAV TSE includes all errors (except horizontal coupling error and the effects of temperature) resulting from the vertical guidance equipment installation. This includes altimeter system errors.
(2) During the final approach segment only (i.e., from the final approach fix to the missed approach point) baro-VNAV TSE must also include horizontal coupling error.
Note: GPS/SBAS Class 2 and Class 3 as well as GPS/GBAS vertical positioning 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.
c. Table 6 is a means to identify the degradation in altimeter performance as altitude increases. But Table 6 is not intended as an exact representation of expected performance 87
characteristics with distinct steps. Instead, altimeter performance degradation is curvilinear as altitude increases. Therefore, to qualify a baro-VNAV system, the 99.7% aircraft altimetry system error for the aircraft (assuming International Standard Atmosphere temperature and lapse rates) must be less than or equal to the following:
𝐴𝐴𝐴 = −8.8 ∗ 10−8 ∗ 𝐻2 + 6.5 ∗ 10−3 ∗ 𝐻 + 50 (ft) where H is the true altitude of the aircraft.
Altitude Region (MSL) Level Flight Segments 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 Notes 1 and 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 RVSM requirements provide acceptable vertical total system error in level flight for the last row in table 6. No additional demonstration or compliance evaluation is required.
However, the altimetry system error cannot be extrapolated to the other altitude blocks.
Note 2: For aircraft type designs prior to April 9, 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: Table 6 does not 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.
d. Flight crew 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.
e. System Displays.
(1) There should be a continuous display of vertical path deviation with the performance indicated in Table 7 below.
Enroute/Terminal (feet) Approach (feet) Full-Scale Deflection (see note 1) ≤ 500 150 (see note 2) Readability ≤ 100 ≤ 30 Minimum Discernable Movement ≤ 10 ≤ 5 Table 7. Vertical Path Deviations Note 1: This is the minimum standard for vertical deviation display scaling and does not preclude using a scale of other than the values listed (e.g. large PFD display) provided that the scaling is suitable to control the aircraft on the intended path.
Note 2: Other values of full-scale deflection for approach may be acceptable provided the proposed value is found satisfactory by an engineering evaluation.
(2) The vertical guidance presentation should be compatible with the aircraft’s flight instrumentation such that the pilot is continuously furnished the aircraft’s vertical deviation with respect to the pre-programmed ascent/descent or level flight profile.
(3) Scale change for the final approach must be done in a manner that supports operational suitability for transitioning onto the final approach segment.
(4) Baro VNAV systems using angular vertical scaling must meet the following:
(a) The deviation scaling supports the FTE monitoring and bounding (75 ft deviation below path).
Note: This may require limiting the length of the approach to exclude operating where the angular deviations no longer support FTE monitoring and bounding.
(b) The deviation limits are equivalent to the operational limits for glideslope deviations during an ILS approach.
f. 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.
g. Additional Constraints.
(1) The baro-VNAV equipment should indicate the aircraft vertical path position to the accuracy specified in paragraph 11-2.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 11-2.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 11-2 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.
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 flight crew to determine system status prior to flight.
(6) The equipment should provide the navigation accuracy specified in paragraph
11-2.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 flight crew prior to arrival at a waypoint for anticipating necessary vertical maneuvering. This indication 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 unless the system is mechanized to the altitude selector in such a manner that a transition to descent or climb will not occur unless the altitude selector has been reset by the flight crew to the new altitude.
(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 11-2.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.
h. The software should be verified and validated to at least level C as defined in RTCA/DO-178B or ‘C’ for baro-VNAV equipment that uses a digital computer.
Chapter 12. General Installation Considerations.
12-1. Introduction.
The following information applies to the installation of all positioning and navigation equipment intended for IFR use.
12-2. 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 GLS 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/ Non-precision Approach (LNAV or RNP
0.3) Non-precision Approach with Vertical Guidance (LNAV/VNAV) LP/LPV Approach GLS Approach Loss of Navigation No Effect Major Major Major Major Misleading Information Minor Major Major Hazardous Hazardous Table 8. Typical Hazard Classifications Note 1: 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.
Note 2: Baro-VNAV vertical guidance is independent from the lateral guidance. Loss of baro -VNAV guidance during an LNAV/VNAV approach results in a fail-down to LNAV or missed approach. Therefore, loss of navigation for baro-VNAV is considered a minor failure condition.
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 93