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(GPS) approach to LNAV minimums at the alternate airport rather than a ground-based approach aid (see paragraph 15-7.1). Additionally, GPS/SBAS equipment may be used on RNAV ‘T’ and ‘Q’ routes within the contiguous U.S. 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.
Note: Refer to the appropriate operating rules and operational guidance documents for equipage requirements.
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. Class 3 and Class 4 GPS/SBAS equipment that complies with the TSO revision ‘b’ or later 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 approved vertical guidance deviation indications for operational credit. 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.
e. GPS/SBAS equipment manufacturers need to use caution when implementing LP capability because some LP procedures cannot support a visual descent angle due to obstructions. The FAS datablock glide path angle field coding uses a zero in these instances.
Equipment manufacturers need to ensure a zero in the glide path angle field does not cause unintended software issues; for example, a divide by zero problem.
f. Manufacturers that request a deviation from the LP capability requirement in TSO C145d/C146d for their Class 3 or Class 4 GPS/SBAS equipment must provide an appropriate limitation for the installation instructions (or equivalent installation documentation) as part of their TSO application package. The limitation must be included in the AFM(S)/RFM(S).
5-3.3 Navigation Database - Data Conversion for GPS/SBAS LNAV/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, Change 1. 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 since it changes the reference system but not the actual vertical location (reference RTCA/DO-200B, Standards for Processing Aeronautical Information, dated June 18, 2015, paragraph 2.4.2)
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 equipment 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 equipment also requires a VHF antenna to receive the GPS/GBAS 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 13-1.1.b, 15-8, and
21-2.3 for installation considerations.
Note: RTCA/DO-253C gives GPS/GBAS equipment manufacturers an option for an antenna/receiver 33
combination or a receiver only. Both can be certified by TSO-C162a.
5-4.2 VHF Data Broadcast Receiving Equipment (TSO-C162a).
The equipment should comply with the RTCA/DO-253C, section 2 requirements as modified by TSO-C162a. The equipment receives the GPS/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 Precision 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-C196(AR) or TSO-C145/C146(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-C196(AR) or TSO-C145/C146(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-C196(AR) or TSO-C145/C146(AR) receiver outputs
(i.e., no GPS/GBAS-provided PVT).
Note 1: The GPS/GBAS positioning service coverage region is defined by Dmax for GPS/GBAS ground stations supporting differential positioning service.
Note 2: These paragraphs are consistent with TSO-C161a.
Applicants may use TSO-C129(AR) GPS receivers if the outputs are shown to be equivalent to TSO-C196(AR).
5-5. GNSS Upgrades.
GNSS equipment 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
15-2.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.
Compatibility 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 additi onal 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(AR) sensor is intended 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
15-6.
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 and 15-6. 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-C146d and the appropriate sections of RTCA/DO-229D, Change 1 as a complete 35
-- system in the aircraft.
c. Using a TSO-C145(AR) or TSO-C196(AR) sensor as a direct replacement for a TSO-C129(AR) sensor may be advantageous to remove performance or operational limitations other than those associated with redundant navigation sources onboard the aircraft even though the complete system retains its original TSO-C129(AR) certification basis. 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 the original TSO-C129(AR) TSOA.
Note: RTCA/DO-229D, Change 1 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 for TSO-C196(AR) equipment or when flying outside of the GPS/SBAS service provider’s coverage area for TSO-C145(AR) equipment.
5-5.3 GPS/SBAS Upgrade.
It is possible to upgrade TSO-C196(AR) equipment to TSO-C145d 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-C145d/C146d compliance. Proposed upgrades for this equipment to TSO-C145d/C146d 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(AR) 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). T SO-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 replacing the original antenna.
(2) If the receiver manufacturer 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-C145/C146 revision ‘b’ or later 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-C145/C146 revision ‘b’ or later 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 TSO-C129 TSOA Antenna/Receiver Combination X X X X X X X X X X X X X X See Note See Note See Note Table 2. Acceptable Standard Antennas 37
--- --- Note: An active TSO-C144 antenna may be acceptable for TSO-C145/C146 revision ‘b’ or later Operational Class 2, 3, and 4 equipment as a receiver, manufacturer-specified antenna per RTCA/DO-229D, paragraph 2.1.1.10.
5-5.5 Marking.
The marking must be modified to reflect the new configuration and approval when equipment is upgraded to a new TSO (such as from TSO-C196(AR) to TSO-C145d 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.
a. For all combined sensor/navigator GNSS equipment, the navigation database is an essential component for the equipment to perform its intended function (see paragraphs 7-1.c and 19-8). Detailed guidance pertaining to the navigation database can be found in AC 20-153 (latest revision).
b. For GNSS equipment to perform its intended function the database configuration, as specified by the equipment manufacturer’s data quality requirements, must be consistent with the equipment capability. Procedures the GNSS equipment does not support should not be accessible to the flight crew (see paragraphs 12-7, 12-8 and 15-5).
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 AFM(S)/RFM(S).
5-6.2 Database Process.
a. The GNSS equipment manufacturer is usually the last link in the aeronautical data processing chain, since 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. The approval of the process is included as part of the TSOA/LODA for GNSS equipment.
b. AC 20-153 (latest revision) defines an acceptable means of qualifying aeronautical database processes. The applicant is encouraged to submit the Compliance Plan early in the development process. Early submittal will allow timely resolution of issues such as tool qualification and database process assurance levels.
c. The data process assurance level needed to support the intended function of the equipment should be defined in the data quality requirements. Data process assurance levels 38
including tool qualification should be verified during the Letter of Acceptance (LOA) review.
5-7. GNSS Geometric Altitude.
GNSS-provided geometric 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 equipment is used to provide positioning inputs to TAWS/helicopter terrain awareness and warning system (HTAWS) equipment. Each type of GNSS equipment described in chapter 5 is acceptable as an input to TAWS/HTAWS equipment.
--- --- Chapter 6. Equipment Performance - RNAV Multi-Sensor Equipment.
6-1. Introduction.
This chapter provides guidance related to the basic functions and performance 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.
a. For area navigation equipment, the navigation database is an essential component for the equipment to perform its intended function (see paragraphs 7-1.c and 19-8). Guidelines pertaining to the navigation database can be found in AC 20-153 (latest revision).
b. For RNAV multi-sensor equipment to perform its intended function the database configuration, as specified by the equipment manufacturer’s data quality requirements, must be consistent with the equipment capability. Procedures the RNAV multi-sensor equipment does not support should not be accessible to the flight crew (see paragraphs 12-7, 12-8 and 16-5).
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.
a. The RNAV multi-sensor equipment manufacturer is usually the last link in the aeronautical data processing chain, since 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. The approval of the process is included as part of the TSOA/LODA for RNAV multi-sensor equipment.
b. AC 20-153 (latest revision) defines an acceptable means of qualifying aeronautical database processes. The applicant is encouraged to submit the compliance plan early in the development process. Early submittal will allow timely resolution of issues such as tool qualification and database process assurance levels.
c. The data process assurance level needed to support the intended function of the equipment should be defined in the data quality requirements. Data process assurance levels including tool qualification should be verified during the LOA review.
6-3. GNSS.
a. When GNSS is integrated in an RNAV multi-sensor system, the GNSS position sensor should comply with the acceptable methods as defined by this AC in paragraph 5-2.2 for 40
GPS not augmented by ground- or space-based systems, paragraph 5-3.2 for GPS/SBAS, and paragraph 5-4 for GPS/GBAS. The GNSS position sensor should be installed in accordance with guidelines provided in chapters 12 through 16 and 19 through 22.
Note: See paragraphs 15-7.8 and 15-9.13 for GNSS installation considerations regarding glidepath low deviation alerting functions.
b. See paragraph 3-4 for TSO-C115(AR) 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 procedure. It is acceptable 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 18-5 of this AC provides additional guidance for baro-VNAV, GPS/SBAS, and GPS/GBAS integrations.
6-4. DME/DME.
The FAA is responsible 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 U.S. airspace meet ICAO standards. These could include non-U.S. 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 facilities listed in the A/FD.
(2) Requiring 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.
If the ARINC 424 FOM is: The aircraft’s DME/DME RNAV system must be:
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.
Note 3: DME facility reasonableness checks are an acceptable means to protect the robustness of DME selection outside the published service volume and FOM limitations, while ensuring no misleading information occurs when using DME/DME positioning.
(4) A valid DME facility:
(a) Broadcasts an accurate facility identifier signal;
(b) Satisfies the minimum field strength requirements; and
(c) Is protected from other interfering DME signals according to the co-channel and adjacent channel requirements.
e. There is no requirement to use VOR, LOC, NDB, IRU or attitude heading reference system (AHRS) during normal operation of the DME/DME RNAV system.
f. When the RNAV system is using a minimum of two DME facilities that satisfy the criteria in paragraph 6-4, and any other valid DME facilities not meeting that criteria, the 95% position estimation error must be better than or equal to 1.75 NM. An FTE contribution not exceeding 1.0 NM (95%) may be assumed for RNAV 2 operations.
Note 1: This performance requirement is met for any navigation system that uses two DME stations simultaneously, limits the DME inclusion angle to between 30° and 150° and uses DME sensors that meet the accuracy requirements of TSO-C66c. If the RNAV system uses DME facilities outside the range identified above, the DME signal-in-space error can be assumed to be 0.1 NM 95%.