ADS-B out. Paragraph 5-2.3 applies to operations that require a prediction program .
b. The following guidelines apply to any prediction program applicable to a particular model TSO-C129(AR) or TSO-C196 receiver that is intended to assess the operational impact of satellite outages for flight planning purposes. Some operators are required to have an approved prediction program. A prediction program with the characteristics described below is acceptable.
Note: The guidelines also apply to prediction programs for TSO-C145/C146(AR) if the equipment is intended for oceanic/remote operations without limitations (see appendix 1 and paragraph 5-3.2.a.
c. TSO-C129(AR) equipment may have either a fault detection only algorithm or an FDE algorithm. TSO-C196 equipment is required by RTCA/DO-316 to have an FDE algorithm. The prediction program must include the appropriate capability for the intended receiver.
d. Operational guidance on predictive RAIM requirements may be found in the Aeronautical Information Manual (or other FAA guidance). The best performance model most likely comes from the original GPS equipment manufacturer.
Note: The FAA/Volpe prediction website did not include FDE prediction capability at the time this AC was published. However, the FAA/Volpe website is scheduled to include FDE prediction capability soon.
e. The prediction program can be provided on any processing platform (in the GPS equipment or not).
f. The prediction program software should be developed in accordance with at least RTCA/DO-178B level D guidelines or equivalent.
g. The program should use either an algorithm identical to that used in the airborne equipment, or an algorithm based on assumptions for RAIM or FDE prediction that give a more conservative result.
h. The program should calculate RAIM or FDE availability based on the same satellite mask angle used in the equipment, but not less than 2 degrees for enroute/terminal operations or 5 degrees for approach.
i. The program should have the capability to manually or automatically designate GPS satellites which are expected to be out-of-service for the intended flight.
j. The program should allow the user to select the intended route (including declared alternates) and the time and duration of the flight. The program should identify the maximum RAIM or FDE outage time, and any predicted navigation capability outages.
(1) For approach operations, the m aximum RAIM or FDE outage duration cannot exceed 5 minutes.
(2) For RNAV 1 and 2 operations, the maximum RAIM or FDE outage duration cannot exceed 5 minutes when TSO-C129(AR) or TSO-C196 receivers are used as the only means of RNAV 1 and 2 compliance.
(3) For oceanic/remote operations, the maximum FDE outage duration cannot exceed 25 minutes for RNP-4 operation, 34 minutes for RNP-10 operation, and 51 minutes for minimum navigation performance standards (MNPS) operation
Note: Prediction programs must use FDE for oceanic/remote operations. See appendix 1.
k. For approach predictions, the program should allow the user to select the destination and expected time of arrival, and provide a RAIM or FDE availability prediction over an interval of at least +15 minutes computed in intervals of 5 minutes or less about the ETA.
l. Prediction programs supporting ADS-B out should meet the requirements in 14 CFR § 91.227. The program should identify the maximum RAIM or FDE outage time, and any predicted surveillance capability outages.
5-3. GPS/SBAS (TSO-C145/C146(AR) receivers).
5-3.1 Antenna.
a. This parag raph provides guidance on acceptable GPS/SBAS antennas. See table 2 for a list of acceptable standard antenna TSOs matched with GPS/SBAS receiver TSO revision and operational class.
b. TSO-C190, that references RTCA/DO-301, defines an acceptable GPS/SBAS antenna.
Note: RTCA/DO-229D, paragraph 2.1.1.10 allows receiver manufacturers to designate manufacturer-specified antennas that take advantage of unique antenna performance rather than using the “standard” antenna defined by TSO-C190.
c. A number of “passive” and “active” antennas were authorized under TSO-C144 for TSO-C145a/C146a compliant GPS/SBAS receivers. These antennas remain acceptable for those receiver installations according to their original TSOA/LODA. Receiver manufacturers are encouraged to use a TSO-C190 antenna whenever a replacement becomes necessary for a TSO-C144 antenna.
d. Major modifications to TSO-C145a/146a receivers that require a new TSOA/LODA upgrade to TSO revision ‘c’ (for operational class 2, 3, and 4) must use either a TSO-C190 or a receiver manufacturer-specified antenna that meets current requirements in RTCA/DO-229D 19
(such as, s ensitivity and dynamic range, geostationary orbit satellite (GEO) bias, broadband interference, and group delay).
5-3.2 Sensor and Sensor/Navigation Computer Configuration.
a. GPS/SBAS equipm ent has two different TSOs depending on whether the equipment is designed as a position sensor only; or, a sensor/navigation computer combination.
TSO-C145c defines an acceptable standard for GPS/SBAS sensors (Class Beta) while TSO-C146c defines a complete sensor/navigation computer configuration (Class Gamma) and an “ILS look-alike” (Class Delta). Both TSOs reference RTCA/DO-229D for operations within and outside of the GPS/SBAS service provider coverage area. When outside of a GPS/SBAS service provider’s coverage area the receivers can revert to using FDE for integrity. The receiver will use GPS/SBAS integrity or FDE; whichever provides the best protection level.
GPS/SBAS equipment will not have any limitations in oceanic and remote areas provided the operator obtains an FDE prediction program (see paragraph 5-2.3).
Note: GPS/SBAS equipment may continue using GEO data and range measurements when outside the GPS/SBAS service provider’s coverage area per the requirements in RTCA/DO-229D (RTCA/DO-229C for TSO revision ‘a’ equipment).
b. GPS/SBAS equipment that complies with the standards implemented by TSO-C145(AR)/C146(AR) does not have an equipment limitation for the aircraft to be equipped with other navigation systems appropriate to the operation. With GPS/SBAS equipment it is also acceptable to flight plan an alternate using an RNAV approach to LNAV minimums at the alternate airport rather than a ground-based approach aid (see paragraph
14-6.1). Additionally, GPS/SBAS equipment may be used on RNAV ‘T’ and ‘Q’ routes within the contiguous United States and Alaska. AC 90-100 (latest revision), contains specific information on performance requirements for RNAV routes. These capabilities should be clearly indicated in receiver manufacturer’s operating instructions.
c. Although GPS/SBAS does not have an equipment limitation for other navigation systems onboard the aircraft, the receiver manufacturer’s operating instructions should encourage operators to retain back-up navigation systems to guard against outages or interference events.
d. GPS/SBAS equipment that complies with the ‘b’ or ‘c’ TSO revision has the capability to do LP approaches. TSO-C145a/C146a manufacturers may provide LP capability in their equipment. LP approaches use the horizontal accuracy and integrity values of LPV but do not provide vertical guidance. The intent is to provide LP approaches only at locations where some issue prevents implementing LPV vertical guidance; so, LP should be the exception rather than the rule. Therefore, LP is not operationally similar to a localizer-only approach on an ILS because LP and LPV are mutually exclusive. That is, LP and LPV lines of minima will never be on the same approach chart.
5-3.3 Navigation Database - Data Conversion for GPS/SBAS L NAV/VNAV Approaches.
a. For LNAV/VNAV approaches collocated with LPV approaches, GPS/SBAS equipment must use the final approach segment (FAS) data block to define the final approach segment as described in RTCA/DO-229D. But, a FAS data block is not provided for stand-alone LNAV/VNAV approaches. The vertical path for such approaches is defined by the threshold location, threshold crossing height, and glidepath angle. However, the altitude of the threshold is published as the height above/below mean sea level (MSL), rather than as the height above/below the WGS-84 ellipsoid. Therefore, the published MSL height (interpreted as a height above/below the WGS-84 geoid) must be converted to height above/below the WGS-84 ellipsoid prior to being used. Actual decision altitude (DA) must be based on the barometric altimeter.
b. The data conversion is not considered alteration of data per RTCA/DO-200A, Standards for Processing Aeronautical Information, dated September 28, 1998, paragraph
2.4.2, since it changes the reference system but not the actual vertical location.
c. Receiver manufacturers may consider performing the conversion within the GPS/SBAS equipment or using a database process that provides threshold crossing height directly as height above/below the WGS-84 ellipsoid for GPS/SBAS approaches. However, GPS/SBAS integrations with baro-VNAV will need to address the issue of WGS-84 ellipsoid versus MSL height. This can be done through conversion or storing threshold data as both WGS-84 ellipsoid and MSL height to use for GPS/SBAS or baro-VNAV as appropriate.
5-4. GPS/GBAS (TSO-C161a/C162a receivers).
The GPS/GBAS equipm ent supports Category I precision approach and, optionally, a GPS/GBAS differentially corrected positioning service (DCPS). When the GPS/GBAS avionics supports both levels of service, whether or not the DCPS is available is determined by the GPS/GBAS ground station. All GPS/GBAS ground stations provide precision approach service; but, not all ground stations are expected to provide DCPS.
5-4.1 Antennas.
a. TSO-C190 that references RTCA/DO-301, defines an acceptable GPS/GBAS antenna.
b. TSO-C162a GPS/GBAS equipm ent also requires a VHF antenna to receive the GPS/GBAS satellite, path, and ground facility information broadcast. Installed antennas approved for ILS localizer/VOR can be used to receive the VDB signals. Unlike ILS ground antenna arrays, a GBAS VHF data broadcast transmitter may be located anywhere on the airport or in its vicinity. This means the VHF broadcast must be received from any direction.
The ILS localizer/VOR antennas may, or may not, be included under TSO-C162a. See paragraphs 12-1.d, 14-7, and 20-2.b for installation considerations.
Note: RTCA/DO-253C gives GPS/GBAS equipment manufacturers an option for an antenna/receiver 21
com bination or a receiver only. Both can be certified by TSO-C162a.
5-4.2 VHF Data Broadcast Receiving Equipment (TSO-C162a).
The equipment should com ply with the RTCA/DO-253C, section 2 requirements as modified by TSO-C162a. The equipment receives the GBAS VDB and outputs the VDB messages to the sensor/navigation computer (see section 5-4.3). TSO-C162a equipment must be used with TSO-C161a, or equivalent, equipment to provide Category I precision approach guidance or PVT based on GPS/GBAS.
5-4.3 Sensor/Navigation Computer (TSO-C161a).
a. Category I P recision Approach.
(1) The equipment should comply with the RTCA/DO-253C, section 2 requirements as modified by TSO-C161a. The equipment outputs lateral and vertical deviations relative to an approach path defined in the VHF data broadcast. The entire precision approach must be contained within the region defined by the broadcast parameter Dmax.
Outside of Dmax, the avionics may not use the differential corrections and the GPS/GBAS equipment will not provide deviations.
(2) GPS/GBAS approaches will not have LNAV/VNAV or LNAV minimums published with the GBAS landing system (GLS) procedure. There is no fail-down option if guidance is lost during a GPS/GBAS final approach.
b. Position Output.
(1) When the GPS/GBAS ground station does not support positioning service, the GPS/GBAS airborne receiver PVT solution must comply with either TSO-C129(AR) class B1 or C1, TSO-C196, or TSO-C145(AR) receiver outputs.
(2) When the GPS/GBAS ground station supports positioning service and the distance (slant range) between the aircraft and the GPS/GBAS reference point is less than or equal to the maximum GPS/GBAS usable distance, Dmax, the GPS/GBAS airborne receiver PVT solution should comply with either TSO-C161a, TSO- C129(AR) class B1 or C1, TSO-C196, or TSO-C145(AR) receiver outputs (i.e., GPS/GBAS-provided PVT possible).
(3) When the GPS/GBAS ground station supports positioning service and the distance (slant range) between the aircraft and the GPS/GBAS reference point is greater than the maximum GPS/GBAS usable distance, Dmax, the GPS/GBAS airborne receiver PVT solution should comply with either TSO- C129(AR) class B1 or C1, TSO-C196, or TSO-C145(AR) receiver outputs (i.e., no GPS/GBAS-provided PVT).
Note: The GPS/GBAS positioning service coverage region is defined by Dmax for GPS/GBAS ground stations supporting differential positioning service.
5-5. GNSS Upgrades.
GNSS equipm ent installations have become very complex due to compatibility issues with the wide range of other installed equipment such as displays, flight guidance systems (FGS), terrain warning systems, etc. GNSS TSOs typically do not include requirements or standards related to installation compatibility or standardized outputs as part of the design and production approval. Therefore, it is recommended that, concurrent with their design and production approvals, equipment manufacturers also pursue an airworthiness approval that includes detailed installation instructions and equipment compatibility lists. See chapter 3 for more information regarding design, production and airworthiness approvals and paragraph
14-2.a for guidance on navigation displays during retrofit installations.
Note: GPS and GPS/SBAS equipment airworthiness approval is not considered novel or unusual per 14 CFR § 21.16 and applicants can use designees during the STC process.
5-5.1 Adding Additional GNSS equipment.
Com patibility must be established between the existing GNSS equipment and whatever new GNSS equipment is added. As an example, some installation applicants may retain existing TSO-C129(AR) equipment and add GPS/SBAS equipment. In this instance, the original TSO-C129(AR) installation should not be re-evaluated, except for modifications made as part of the GPS/SBAS installation. The re-evaluation should be to the affected functions or performance. For example, if the equipment shares a GNSS antenna there will be additional signal loss for the original equipment and compliance to the original TSO-C129(AR) installation instructions should be verified.
5-5.2 Replacing GNSS Equipment.
a. The TSO-C196 sensor is intend ed as a direct replacement for a TSO-C129(AR) Class B or C sensor provided the installation applicant or TSOA/LODA holder ensures compatibility with the display and navigation computer. The complete sensor/navigation computer/display system will continue to have the limitations noted in paragraphs 5-2.2.a and
14-5.
b. It is also possible to use either a TSO-C145(AR) sensor or a combined TSO-C145(AR)/C146(AR) Class Delta-4 sensor to replace a TSO-C129(AR) Class B or Class C sensor provided the installation applicant or TSOA/LODA holder ensures compatibility with the display and navigation computer. In such a sensor replacement, the aircraft operator can derive additional benefits and navigation capability such as removing the limitations noted in paragraphs 5-2.2.a and 14-5. However, the benefits do not automatically extend to enabling GPS/SBAS-provided LNAV/VNAV or LP/LPV capability. See paragraph 3-2 for compliance to TSO-C146c and the appropriate sections of RTCA/DO-229D as a complete system in the aircraft.
c. Using a TSO-C145(AR) or TSO-C196 sensor as a direct replacement for a TSO-C129(AR) sensor may be advantageous to remove performance or operational limitations 23
other than those associated with redundant navigation sources onboard the aircraft even though the com plete system remains TSO-C129(AR). For example, the sensor processing improvements obviate the need to perform a RAIM prediction check 2 NM (nautical miles) prior to the final approach fix (FAF) as required by TSO-C129(AR).
Note: RTCA/DO-229D and RTCA/DO-316 both have a fault detection prediction requirement that applicants can use to perform the prediction check if needed for integration compatibility. But, the equipment requirement is there primarily to support an operational requirement for pre-departure fault detection checks when flying outside of the GPS/SBAS service provider’s coverage area.
5-5.3 GPS/SBAS Upgrade.
It is po ssible to upgrade TSO-C196 equipment to TSO-C145c compliance. Receiver manufacturers who provide an upgrade path are encouraged to use an STC-AML to streamline the installation approvals (see paragraph 2-3).
Note: It may be difficult to upgrade TSO-C129(AR) or TSO-C145a/C146a equipment to TSO-C145c/C146c compliance. Proposed upgrades for this equipment to TSO-C145c/C146c will have to be carefully evaluated.
5-5.4 GNSS Antenna Re-Use/Replacement.
a. There are no re-use or replacement possibilities for antennas certified under TSO-C129/C129a as part of the receiver TSOA/LODA. For receiver/antenna combinations certified by this method to use a different antenna design or specification is a major design change that invalidates the original TSOA/LODA.
b. For a TSO-C129/C129a receiver, it is possible to replace the original antenna if the antenna was certified to a separate antenna TSO. In this case, a TSO-C190 antenna, or antennas approved under TSO-C144(AR), can be used as replacements for any class of TSO- C129/C129a receiver.
c. For TSO-C196 receivers it is possible to re-use or replace both “active” and “passive” antennas approved under TSO-C144(AR). TSO-C190 “active” antennas can be used as well.
d. For TSO-C145/C146(AR) operational Class 1 receivers; and, all classes of TSO-C145a/C146a receivers (see note below), it is possible to re-use both “passive” and “active” antennas approved under TSO-C144(AR). TSO-C145/C146(AR) operational Class 1 receivers are limited to enroute through LNAV approaches.
(1) The standards for equipment previously certified to TSO-C145a/C146a do permit using either TSO-C144 “passive” or “active” antennas for all receiver operational classes. However, receiver manufacturers are encouraged to use a TSO-C190 antenna when 24
replacing the original antenna.
(2) If the receiver m anufacturer chooses to not use a TSO-C190 antenna, they should use a TSO-C144 “active” antenna that complies with the intra-system noise environment, test procedures/methodologies, and 25 nanosecond differential group delay requirements found in RTCA/DO-301. Failure to do so may cause performance degradation due to GEO bias and an increasing broadband interference noise environment.
e. For TSO-C145b/C146b/C145c/C146c operational Class 2, 3, or 4 receivers, “Passive” TSO-C144(AR) antennas cannot be re-used. TSO-C190 describes the standard “active” antenna for TSO-C145b/C146b/C145c/C146c operational Class 2, 3, or 4 receivers. It may be possible to re-use an “active” TSO-C144 antenna for these receivers as a manufacturer-specified antenna per RTCA/DO-229D, paragraph 2.1.1.10.
f. In all cases a TSO approval does not guarantee antenna/receiver installation compatibility. Installation compatibility must be established by the antenna or receiver manufacturer and documented in the approved installation instructions. Also, there can be 14 CFR § 21.611 issues related to major versus minor alterations. Each project must be evaluated according to 14 CFR § 21.611 to address the alteration regulatory issues.
TSO-C144(AR) Passive TSO-C144 Active TSO-C190 Antenna Type Receiver Type TSO-C129 TSOA Antenna/Receiver Combination TSO-C145a/C146aAll Classes TSO-C145b/C146b/C145c/C146cOpn’lClass 1 X X X TSO-C145b/C146b/C145c/C146c Opn’lClass 2,3,4 X X X X X TSO-C129/C129aAll Classes TSO-C196GPS X X X TSO-C129/C129a Combined Rec/Ant X X X See Note See Note See Note TSO-C144(AR) Passive TSO-C144 Active TSO-C190 Antenna Type Receiver Type TSO-C129 TSOA Antenna/Receiver Combination TSO-C145a/C146aAll Classes TSO-C145b/C146b/C145c/C146cOpn’lClass 1 X X X TSO-C145b/C146b/C145c/C146c Opn’lClass 2,3,4 X X X X X TSO-C129/C129aAll Classes TSO-C196GPS X X X TSO-C129/C129a Combined Rec/Ant X X X See Note See Note See Note
Table 2. Acceptable Standard Antennas
Note : An active TSO-C144 antenna may be acceptable for TSO-C145b/C146b/C145c/C146c Operational Class 2, 3, & 4 equipment as a receiver manufacturer-specified antenna per RTCA/DO-229D, paragraph 2.1.1.10.
5-5.5 Marking.
The m arking must be modified to reflect the new configuration and approval when 25
26 equipment is upgraded to a new TSO (such as from TSO-C196 to TSO-C145c Operational Class 1). This marking change can be accomplished by a certificated person in accordance with the TSOA/LODA holder’s instructions. A certificated person in this context is defined as one who is authorized under 14 CFR § 43.3, persons authorized to perform maintenance, rebuilding, and alterations.
5-6. Navigation Database.
For all com bined sensor/navigator GNSS equipment, the navigation database is an essential component for the equipment to perform its intended function. Guidelines pertaining to the navigation database can be found in AC 20-153 (latest revision). Particular attention should be paid to the specification of the data quality requirements as described in RTCA/DO- 200A, appendix B.
5-6.1 Database Installation Instructions.
The TSOA/ LODA installation instructions/manual must contain a limitation identifying the requirements for the navigation database. This limitation will also be included in the AFMS/RFMS.
5-6.2 Database Process.
The RNAV multi-s ensor equipment manufacturer is usually the last link in the aeronautical data processing chain, as the format for the data loaded in the final database is typically proprietary. The applicant for a TSOA/LODA must identify an aeronautical data process accessible to the equipment users. AC 20-153 (latest revision), Acceptance of Data Processes and associated Navigation Databases, provides an acceptable method for this aeronautical data process. The approval of the process is included as part of the TSOA/LODA for GNSS equipment.
5-7. GNSS Geometric Altitude.
GNSS-provided geom etric altitude is not adequate for compliance with air traffic control altitude requirements in the National Airspace System (NAS) or internationally. The primary barometric altimeter must be used for compliance with all air traffic control altitude regulations, requirements, instructions, and clearances. GNSS geometric altitude may be used to increase situation awareness, but must be clearly distinguished from a barometric source.
The label GSL may be used to indicate GNSS sea level.
5-8. Terrain Awareness and Warning System (TAWS).
GNSS equipm ent is used to provide positioning inputs to TAWS equipment. Each type of GNSS equipment described in chapter 5 is acceptable as an input to TAWS equipment.
Chapter 6. Equipment Performa nce - RNAV Multi-Sensor Equipment.
6-1. Introduction.
This chapter provides guidance related to the basic functions and perform ance of a multi-sensor unit. This chapter identifies issues associated with equipment performance that applies to all types of equipment. Each individual sensor must meet the navigation performance and operation criteria contained in the respective TSO and AC applicable to that type sensor.
6-2. Navigation Database.
For area navigation equipm ent, the navigation database is an essential component for the equipment to perform its intended function. Guidelines pertaining to the navigation database can be found in AC 20-153 (latest revision). Particular attention should be paid to the specification of the data quality requirements as described in RTCA/DO-200A, appendix B.
6-2.1 Database Installation Instructions.
The TSOA/ LODA installation instructions/manual must contain a limitation identifying the requirements for the navigation database. This limitation will also be included in the AFMS/RFMS.
6-2.2 Database Process.
The RNAV multi-s ensor equipment manufacturer is usually the last link in the aeronautical data processing chain, as the format for the data loaded in the final database is typically proprietary. The applicant for a TSOA/LODA must identify an aeronautical data process accessible to the equipment users. AC 20-153 (latest revision), Acceptance of Data Processes and associated Navigation Databases, provides an acceptable method for this aeronautical data process.
6-3. GNSS.
a. When GNSS is integrated in an RNAV m ulti-sensor system, the GNSS position sensor should comply with the acceptable methods as defined by this AC in paragraph 5-2.2 for GPS not augmented by ground- or space-based systems, paragraph 5-3.2 for GPS/SBAS, and paragraph 5-4.2 for GPS/GBAS. The GNSS position sensor should be installed in accordance with guidelines provided in chapters 11 through 15 and 18 through 21.
Note: See paragraphs 14-6.8 and 14-8.16 for GNSS installation considerations regarding ground proximity warning system (GPWS) or TAWS alerting functions.
b. See paragraph 3-2 for TSO compliance guidance on RNAV multi-sensor equipment integrating GPS/SBAS capability. RTCA/DO-229D, section 2, addresses the use of GPS/SBAS vertical position (referenced to WGS-84 ellipsoid) as used on the final approach segment of an LNAV/VNAV or LPV approach procedure or as advisory guidance on an LNAV approach 27
procedure. It is acceptab le to provide advisory vertical guidance for LP approaches using the method described in RTCA/DO-229D for LNAV (see paragraph 4-2.d).
c. See paragraph 3-3 for TSO compliance guidance on RNAV multi-sensor equipment integrating GPS/GBAS capability.
d. Many RNAV multi-sensor systems have implemented baro-VNAV for use in all phases of flight, and baro-VNAV can be used for vertical guidance on an LNAV/VNAV approach procedure.
(1) The RNAV multi-sensor system manufacturer should address the GPS/SBAS and/or GPS/GBAS integration issues associated with equipment designs that also include baro-VNAV capability. In particular the RNAV multi-sensor equipment must provide a smooth guidance transition between baro-VNAV and GPS/SBAS and/or GPS/GBAS vertical guidance and a clear mode annunciation to the pilot.
(2) Paragraph 17-5 of this AC provides additional guidance for baro-VNAV, GPS/SBAS, and GPS/GBAS integrations.
6-4. DME/DME.
The FAA is responsib le for evaluating DME/DME coverage and availability against a minimum standard DME/DME RNAV system for each route and procedure. This paragraph defines the minimum performance and functions (baseline) for DME/DME RNAV systems intended to support RNAV 1 and RNAV 2 routes, as well as RNAV 1 departure procedures (DPs) and standard terminal arrival routes (STARs).
a. The DME/DME RNAV system must:
(1) Provide position update within 30 seconds of tuning DME navigation facilities.
(2) Auto-tune multiple DME facilities.
(3) Provide continuous DME/DME position updating.
Note: Given a third DME facility or a second pair has been available for at least the previous 30 seconds, there must be no interruption in DME/DME positioning when the RNAV system switches between DME stations/pairs.
b. The FAA cannot ensure all DME signals within reception distance of United States airspace meet International Civil Aviation Organization (ICAO) standards. These could include non-United States DME facilities, or Department of Defense (DOD) maintained DME facilities excluded from the NAS database. DME/DME RNAV procedure design will only use DME facilities listed in the airport/facility directory (A/FD). Although a procedure design issue, applicants may mitigate this restriction by:
(1) Having the DME/DME RNAV system only use DME f acilities listed in the A/FD.
(2) Require exclusion of non-NAS DME facilities from the aircraft’s navigation database when the RNAV routes or procedures are within reception range of these non-NAS DME facilities.
(3) Demonstrating to the FAA that their RNAV system performs reasonableness checks to detect errors from the non-NAS DME facilities and excludes these facilities from the navigation position solution when appropriate (e.g., using the ARINC 424 coding to preclude tuning co-channel DME facilities when the signals-in-space overlap). See paragraph 6-4.1 for guidance on reasonableness check testing.
c. When needed to generate a DME/DME position, the DME/DME RNAV system (also referred to as a FMS) must use, as a minimum, DMEs with a relative angle between 30 and 150. The FMS may use DME pairs outside these angles (for example, 20 to 160).
d. The RNAV system may use any receivable DME facility (listed in the A/FD) regardless of its location. When needed to generate a DME/DME position, as a minimum, the RNAV system must use an available and valid low altitude and/or high altitude DME anywhere within the following region around the DME facility:
(1) Greater than or equal to 3 NM from the facility;
(2) Less than 40 degrees above the horizon when viewed from the DME facility;
and
(3) For facilities with an ARINC 424 figure of merit (FOM), the RNAV system may use the FOM value from table 3 as the acceptable, usable region.
The aircraft’s DME/DME RNAV system must be: If the ARINC 424 FOM is:
Less than or equal to: And less than:
0 40 NM from the facility 12,000 ft above facility elevation 1 70 NM from the facility 18,000 ft above facility elevation 2 130 NM from the facility -- 3 160 NM from the facility -- Table 3. DME Usable Range
Note 1: RNAV systems may use additional DME facilities (for example, a localizer (LOC)/DME facility may be used but is not required to be used for positioning). RNAV systems are not required to use the FOM value.
Note 2: RNAV routes and procedures may include new FOMs with expanded service volumes.