Appendix A Elimination of slant range error and its attendant compensating procedures is prerequisite to the development of optimum routes and separation criteria. FAA plans to initiate rulemaking action in the near future requiring slant range correction in terminal hubs and at FL 180 and above. This level may be lowered as operational experience is gained.
2. ACCETPABLE MEANS OF COMPLIANCE (FOR USE UNDER INSTRUMENT FLIGHT RULES) An acceptable means of compliance with Section -.1301, -.1309, -.1431, and -.1581, of Part 23, 25, 27 or 29 (as applicable), with respect to area navigation systems, provided for use under IFR conditions, is to satisfy the criteria set forth in this paragraph.
a. Accuracy.
(1) 2-D RNAV System using Reference Facility for continuous navigation information. The total of the error contributions of the airborne equipment (receivers plus area navigation - including desired track setting as well as waypoint setting errors) when combined RSS with the following specific error contributions should not exceed the error values shown in Table 1, Appendix A VOR ground station + 1.9° DME ground station + 0.1 NM 2-D RNAV systems which use VOR/DME information from other than the Reference Facilities must show that the algorithm used will always select a station that will provide cross track/along track errors equal to or less than the greater of the RNAV system errors of the reference facility for any RNAV track (Table 1) or the errors shown in paragraph 2.a. (3).
2-D RNAV System not using VOR/DME for continuous navigation information. The total of the error contributions of the airborne equipment (including update, aircraft position and computational errors), when combined with appropriate flight technical errors listed in 2.a. (4) below, should not exceed the following with 95% confidence (2-sigma) over a period of time equal to the update cycle:
Cross Track Along Track Enroute 2.5 NM 1.5 NM Terminal 1.5 NM 1.1 NM Approach 0.6 NM 0.3 NM
(4) 2-D Flight Technical Errors (FTE) when combined RSS with the errors discussed in (1) and/or (a) above determine the Total Page 2 Par 1
Appendix A System error. The Total System error is used by airspace planners and includes the following specific FTE values for determining cross-track position accuracies. Values larger than these must be offset by corresponding reduction in other system errors. (See Appendix C) No FTE is used in determining the along-track accuracy.
Enroute + 2.0 NM Terminal + 1.0 NM Approach + 0.5 NM
(5) 3-D RNAV Systems. The total of the error contributions of the airborne equipment, including sensors and area navigation:
(a) Should not contribute any new horizontal error, and
(b) When combined RSS with the specific vertical error contributions for "Flight Technical" listed in Table B of this Appendix, should not exceed the total RSS accuracy requirements of Table B, Appendix A.
(c) Vertical Navigation Equipment (VNAV) Total vertical navigation system accuracy criteria are based largely on the satisfactory experience of many years with the present separation standard of 1000 feet, while also anticipating the probable needs of the air traffic system in the future.
The total 3-D system accuracy requirements for level flight are stated in Table A. The requirements are based on final approach, terminal area, and enroute operations in level flight. The specific requirements are based on the obstacle clearance standards for final approach and on airspace protection standards up to FL 290. The requirements for operations above FL 290, where separation standards change, are based on performance levels typical of altimetry systems meeting accuracy requirements for final approach and enroute operations up to FL 290.
The 3-D system accuracy for other than level flight varies with the ascent/descent angle. This variance is due to the flight technical error which has been shown to vary with the angle of ascent or descent. These variations are shown in Table B.
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Appendix A
MINIMUM ACCURACY REQUIREMENTS FOR VERTICAL GUIDANCE EQUIPMENT
EMPLOYED IN AIRBORNE VERTICAL NAVIGATION SYSTEMS Level Flight Flight Altitude Total Vertical Error Segment Region in Feet (30) (99.7% confidence) Remarks Final At or below 200 Meets the obstacle clearance Approach 5000' MSL requirements of 250'.
Terminal At or below 350 Meets the 1000' level flight Area 10000' MSL vertical separation requirement.
Enroute All altitudes 350 Meets the 1000' level flight vertical separation requirement.
TABLE A Table B illustrates typical error budgets where errors are assumed to be independent and are combined by the root-sumsquare (RSS) method. These accuracy requirements provide an adequate buffer zone to accommodate all normally encountered atmospheric anomalies and reference discrepancies without jeopardizing the validity of the 1000 foot vertical separation standard in level flight.
The table lists vertical position error budgets without regard for horizontal position uncertainty. In a dynamic situation, additional vertical errors must be considered during ascending and descending flight because the aircraft may be either ahead of or behind its assumed position along track. For systems meeting minimum horizontal position accuracy requirements, this additional error is generally larger than the non position-dependent vertical position errors shown. The airborne computer calculates the descent angle and commands an altitude for the assumed position.
If the aircraft is behind the assumed position, the aircraft is below the intended track by an amount proportional to the along-track error. This error must be added (RSS) to the basic vertical position errors shown when calculating airspace protection and obstacle clearance during descent.
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Appendix A
SUMMARY OR REPRESENTATIVE VERTICAL GUIDANCE ERROR BUDGET IN FEET 99.7% (30) *Final Approach *Terminal Enroute (1) Error 5000 feet MSL 10,000 feet ¡All altitudes Source and below MSL and below Level Ascent or Level Ascent or! Level Ascent or Flight Descent Flight Descent Flight Descent Altimetry (3) 90 140 200 265 250 350 NAV Equipment (4) 100 100 150 150 0 (2) 220 Flight Technical (5) 150 200 250 300 250 300 TOTAL RSS (30) 200 265 350 430 350 510
TABLE B NOTE 1. Maximum operating altitudes to be predicated on compliance with total accuracy tolerance.
*When final approach and terminal area procedures are developed above altitudes shown, error is increased proportionately in the altimetry and RNAV parameters to provide airspace and obstacle clearance protection.
NOTE 2. In the event that WAV guidance is used in level flight enroute the incremental error component contributed by the VNAV equipment must be offset by a corresponding reduction in other error components, such as flight technical error, to ensure that the total error budget is not exceeded.
NOTE 3. Altimetry Error. Refers to the electrical output and includes all errors attributable to the aircraft altimetry installation including position effects resulting from normal aircraft flight attitudes. In high performance aircraft, it is expected that altimetry correction will be necessary to meet these requirements. Such correction should be done automatically. In lower performance aircraft, upgrading of the altimetry system may be necessary. The larger errors shown for ascent/descent are typical of automatically corrected altimeter systems which meet the level flight error budget.
NOTE 4. VNAV Equipment Error. Includes all errors resulting from the vertical guidance equipment installation. Does not include Par 2 Page 5
Appendix A errors of altimeter system but does include any additional errors resulting from the addition of the VNAV equipment.
This error component may be disregarded in level enroute flights if the operation is limited to guidance by means of the altimeter only. It should not be disregarded in the terminal and approach operations, where the pilot is expected to follow the VNAV indications.
NOTE 5. Flight Technical Error. Includes errors in pilot interpretation of vertical guidance instrumentation, pilot activation of aircraft vertical controls, and deviations caused by aircraft response characteristics. Consideration is given to the relatively high pilot proficiency and good aircraft characteristics expected to be found in most operations at the higher altitudes. These values represent consensus estimates based upon experience and some limited testing; and for cases in which there is no relevant experience, they are conservative estimates. It is recognized that there are several design and operational parameters that could affect those values including display configuration, autopilot coupling versus manual control, pilot workload, and variation of aircraft response with increasing gross weight and altitude.
As operational experience and experimental data are accumulated and analyzed, the values will be suitably adjusted.
(6) All RNAV equipment approved for use under Instrument Flight Rules (IFR) must meet the appropriate accuracy criteria.
Authorized."
(7) Equipment presented will be approved by issuance of an STC or, upon prior approval from the appropriate regional office, may be approved by a properly processed Form 337 in the field.
b. Area Navigation System Design.
(1) General. The systems will normally use VOR/DME input sensor signals (or use combinations of VOR and DME for updating purposes) and indicate aircraft positions relative to the RNAV route and selected waypoint. Systems may be designed to utilize other Page 6 Par 2
Appendix A sensor inputs if equivalent accuracy can be demonstrated.
Installations intended for final approach should use position information that is essentailly continuous with interruptions no longer than would result from switching from one preprogramed waypoint to another. The system should give no operationally significant misleading information.
(2) Vertical Guidance Input Controls.
In the absence of pre-stored or automatically inserted flight profile parameters, pilot controls shall provide for at least the following inputs:
Station Elevation. For systems employing slant range error correction, elevation of the VOR/DME ground station in increments not greater than 100 feet if used during final approach, and for other phases in increments not greater than 1000 feet.
Waypoint. Waypoint altitude in increments not greater than 10 feet if used during final approach, and for other phases in increments not greater than 100 feet. Waypoint ¡posteton anal " the scation of the greater than 0.1 nautical mile or 0.2 degree bearing from horizontal position shall be entered in increments not the station or the equivalent.
(c) Flight Path Angle. Vertical gradient from a zero degree origin in increments not greater than 0.1 degree or the equivalent.
(3) Checking of Input. Provisions should be made to enable the pilot to check the correctness of the inputs.
(4) Altimeter Setting. The system shall be so designed that there is no requirement to insert separate barometric correction inputs into the vertical guidance computer. Adjusting one of the barometric pressure altimeters in the cockpit should automatically provide the corrected input to the vertical computer. In order to avoid the abrupt irregularity in the computer vertical flight path at the transitional level, the pilot will make altimeter setting changes between local and standard 29.92" Hg. above the transitional level. Airspace will be buffered above this level to account for the discontinuities in the vertical flight path and the pilot will be expected to make the change gradually so as not to introduce unacceptably abrupt flight path requirements.
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Appendix A Vertical Guidance Display. The equipment shall provide a vertical guidance presentation compatible with the aircraft's flight instrumentation such that the pilot is continuously furnished vertical deviation of the aircraft with respect to a preprogramed ascent/descent or level flight profile.
(6) Failure Warning. Provision should be made to alert the crew upon occurrence of any probable failure of major system functions or loss of inputs, including those that would affect aircraft position, heading, command course, command heading, altitude, or vertical guidance indications.
(7) Performance Check. Provision should be made for checking the system's performance on the ground and in flight. This may be a built-in check, an auxiliary test system or a procedural check.
Response Time. The navigation display should indicate aircraft position, to the accuracy specified in Paragraph 2.a., assuming that navigation sensor outputs are available:
(a) During flight in any direction at the maximum ground speed declared by the equipment manufacturer, and
(b) During ascent or descent at the maximum rates declared by the equipment manufacturer, and
(c) Within five seconds after any normal maneuver, assuming sensor inputs are not lost during the maneuver.
(d) The time lag between time of data input and guidance derived from the display of the data should not be operationally significant.
NOTE: Terminal area speed limitations are taken into account in connection with this provision. Moving elements of the navigation display may be damped.
Coordination of Displays. In installations incorporating ›otn horizontal and vertical guidance, there should be no operationally significant difference between the various displays used by the flight crew. For example, if a descent is programmed to end at a waypoint, the command to level off should be operationally coincidental with the waypoint indication. This is not intended to preclude maneuver anticipation.
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Appendix A Environmental Conditions. The area navigation equipment should be capable of satisfying the criteria set forth in Paragraph
2.a. and 2.b. above over the environmental ranges expected to be encountered in actual aeronautical operations. In demonstrating compliance, the environmental conditions outlined in Radio Technical Commission for Aeronautics Document DO-138 titled "Environmental Conditions and Test Procedures for Airborne Electronic/Electrical Equipment and Instruments dated June 27, 1968, or other appropriate environmental standards may be used.
(11) Auto Tune Systems. Systems which automatically tune/select VOR/DME facilities for navigation or update should be limited to a search range of 130 NM for high altitude facilities and 40 NM at 18,000 feet and below for low altitude facilities in keeping with the NAS frequency protection criteria unless through computer logic or a 'reasonableness test' faulty information is rejected.
(12) Turn Anticipation and Parallel Offset.
RNAV systems which provide for parallel offset tracks must also limit the turning maneuver. Turns shall be anticipated and flown in such a way as to cause the aircraft to remain within + 2.5 NM of the desired track centerline enroute and + 1.5 NM of the centerline in the terminal area. Pilots flying systems which do not automatically anticipate the turn are expected to lead a turn by 1 NM per 100 knots true airspeed.
(b) 3-D systems shall not require additional controls to assure that the offset route is in the same horizontal plane as the parent route at the waypoint. The plane is measured on the bisector angle between centerlines of the adjacent route segments.
c. Area Navigation Equipment Installation.
Location of the RNAV display. Each display element to be used as a primary flight instrunent 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 his normal position and from his line of vision when he is looking forward along the flight path.
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Appendix A
(2) Failure protection. Any probable failure of the airborne area navigation equipment should not derogate the normal operation of required equipment connected to it, nor cause a flight hazard.
(3) Radio frequency interference. The area navigation equipment should not be the source of objectionable radio frequency interference,nor be adversely affected by radio frequency emissions from other equipment in the aircraft.
Manufacturer's instructions. The area navigation equipment should be installed in accordance with instructions and limitations provided by the manufacturer.
Aircraft Flight Manual. If an aircraft flight manual is provided by the aircraft manufacturer, its FAA approved portion may contain the following information on the area navigation equipment:
(1) Normal procedure for operating the equipment;
(2) Equipment operating limitations; and,
(3) Emergency operating procedures (if applicable).
If not contained in the aircraft flight manual, information on equipment operating limitations should be provided to the pilot by means of placards. The aircraft flight manual or placard should state "RNAV Instrument Approaches Not Authorized" if the instrumentation is such that FIE cannot be resolved to meet appropriate criteria. Revisions or supplements to the flight manual must be approved by the Regional Chief of the Engineering and Manufacturing Branch.
3. TESTING PROCEDURE FOR EQUIPMENT PROVIDED FOR USE UNDER INSTRUMENT
FLIGHT RULES) General. An applicant for approval of an area navigation system installation in an aircraft may show that he has satisfied the criteria in Paragraph 2 by a combination of bench tests of the individual components (including VOR and DME) and ground/flight tests of the entire installed area navigation system. The bench tests may have already been performed by the individual component manufacturer (during design and construction) or by the installer (on behalf of a previous customer). Such bench test data, if certified by the manufacturer or installer are acceptable. In addition, the applicant may refer to applicable TSO standards, if the manufacturer of the equipment certifies that his equipment meets those standards.
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Appendix A
b. Bench Tests. The following tests may be performed on the bench or with the navigation system installed in the aircraft:
Test equipment. Bench test equipment should be capable of simulating the input signals from VOR/DME and/or the altimeter or other sensors and of varying those signals over the ranges for which the equipment is designed.
(2) Accuracy testing.
(a) Variables to be considered. Each variable that has a significant effect on position error should be investigated over its entire range, and the error analysis should show the effects of reasonably probable variations of these variables on total system accuracy. The statistical technique described in RICA Document No. DO-153 entitled Minimum Performance Standards -- Airborne VOR Receiving Equipment Operating Within the Radio Frequency Range of 108-118 Megahertz" dated August 18, 1972, may be used as a guide.
(b) Static test. Horizontal and/or vertical position accuracy should be measured statically as the error in displayed position relative to the theoretical position obtained from perfect signal inputs (range and bearing from a knowi station location and/or altitude). Simulated range and bearing and/or altitude signals are introduced into the area navigation equipment. Combinations of ranges from zero up to the maximum distance for which the equipment is designed, bearings from zero to 360 degrees, and altitudes up to the maximum certificated altitude for the set of input signals, the corresponding display output aircraft should be inserted as input signals. For each compared to the the creal should be compared to the theoretical position and recorded as an RNAV system error. The errors for each test point are then combined statistically to determine the 26 (95%) probable error. When this value exceeds the RNAV system error element shown on Table 1, the total horizontal systen error must be computed by adding the RNAV system error RSS to the other system errors. See Appendix C.
They should be within the values shown in Table 1 if the system is to be used in IF flight. Note that only one error table is provided. This represents the required accuracy for IFR of VOR/DME equipment using the reference facility. The only variable between enroute, terminal, and approach is FIE (shown in 2.a. (4) above). Separate Par 3 Page 11
Appendix A The vertical system error is computed by adding RSS the values for FTE (Table B) and altimetry appropriate to the installation.
The values shown in Table 1 and the RSS totals in Table B should not be exceeded.
(c) Dynamic test. In addition to the static test, a dynamic accuracy test should be performed utilizing simulated VOR/DME and/or altimeter inputs varied in range, bearing and/or altitude in order to assess the ability of the system to smooth variable input signals without incurring excessive lag. These tests should be performed with representative simulated airspeeds throughout the range for which the equipment is designed. During these tests the measured RNAV equipment error should be consistent with the total system accuracies specified in Paragraph 2.
Alternatively, an in-flight demonstration of satisfactory dynamic characteristics may be accepted.
Systems having map type displays. If the system uses a map type pictorial display of aircraft position as a primary means of steering guidance, the accuracy determination should take into account any error contribution by the cartography.
Altimetry tests. The accuracy of the installed altimetry system should be determined by tests, evaluation of previously approved data, or both, to assure that the altimetry error budget of Table B is not exceeded. Static system error determined during aircraft certification or determined by currently recognized means may be combined RSS with scale error data for the altimeter.
Ground/flight tests.
(1) Ground tests. After the area navigation system has been installed, but before the aircraft is flown, an operational/ functional check should be performed to ensure that the system has been installed in accordance with the installation criteria in Paragraph 2.c. (and with all applicable airworthiness regulations) and that it functions properly and safely.
(2) Determination of when flight tests are necessary. At least one flight test for accuracy in the approach case is necessary. Additional flight tests for accuracy are necessary if the system accuracy is not adequately determined by signal simulation as described in 3.b. above, or if it appears that the resolution of the pilot display is such Page 12 Par 3
Appendix A That the assumed FTE of 2.0 NM (enroute), 1.0 NN (terminal) or 0.5 N (approach), will be exceeded.
NOTE: The "Approach" mode is defined as the flight operation between the final approach waypoint and the airport. The "Terminal" mode is defined as the ingress/egress flight operation between Inroute and Approach, normally below FL 180 within 50 miles of the airport. The "Enroute" mode is defined as the cruising flight operation between Terminal areas.
Accuracy tests in flight. When the bench check data required by paragraph 3.b. above are not available, flight tests are necessary. Therefore, in addition to ground tests, to demonstrate satisfactory performance of the area navigation equipment, the airplane should be flown solely by reference to the RNAV display and other standard flight instruments, at a relatively low altitude under VFR conditions, with a safety pilot, and if practicable under ground radar surveillance as follows:
(a) Along the length of an FAA approved RAV route segment.
(b) In accordance with an FAA approved RNAV terminal area procedure; and
(c) In accordance with an FAA approved RNAV approach procedure.
(d) During ascent and descent flight in terminal and/or final approach operation with theodolite observation or equivalent to check vertical angle performance of 3-D RNAV.
Final approach performance may be compared against ILS signals.
in each case, the area navigation system is satisfactory if the equipment meets the accuracy requirements of Paragraph 2.a.
as determined by direct visual reference or other suitable methods to identifiable ground check points and a large scale map of the area on which are shown route segment centerlines and boundary widths applicable to the distance from the reference facility.
Functional test in flight. The area navigation system should be checked out in flight to determine whether the design and installation criteria in Paragraph 2.b. and 2.c. are satisfied.
ACCEPTABLE MEANS OF COMPLIANCE (FOR EQUIPMENT PROVIDED FOR USE UNDER
VISUAL FLIGHT RULES ONLY) a ta, off at 251, Sect as applicable), with Par 3 Page 13