CS ACNS.D.ADSB.080 Data Sources as defined by Mode S Elementary and Enhanced Surveillance
ED Decision 2013/031/R
(See AMC1 ACNS.D.ADSB.080)
The data source requirements as defined for in section 2 and 3 of this subpart, are applicable.
AMC1 ACNS.D.ADSB.080 Data sources as defined by Mode S elementary and enhanced surveillance
ED Decision 2022/008/R
(a) General requirements
For the requirements and general guidance on the data sources providing the Mode S elementary and enhanced surveillance parameters, the following references to CS ACNS.D.ELS and CS ACNS.D.EHS apply:
(1) Aircraft Identification: CS ACNS.D.ELS.030(a)(3);
(2) Mode A Code: CS ACNS.D.ELS.030(a)(1);
(3) SPI: CS ACNS.D.ELS.030(a)(2);
(4) Emergency Mode/Status: CS ACNS.D.ELS.030(a)(1);
(5) Pressure Altitude: CS ACNS.D.ELS.025;
(6) MCP/FCU Selected Altitude: AMC1 ACNS.D.EHS.015(c)(1);
(7) Barometric Pressure Setting:AMC1 ACNS.D.EHS.015(c)(3);
(8) ACAS Operational/Resolution Advisory: AMC1 ACNS.D.ELS.015; and
(9) ICAO 24 bit Address: CS ACNS.D.ELS.050.
(b) Emergency Status
When transmitting the Mode A emergency status codes, the additional specific bits should be set (see Appendix H, Part 1, Definition 10).
(c) Pressure Altitude — NICbaro
For aircraft with an approved, non-Gillham altitude source, the Barometric Altitude Integrity Code ‘NICbaro’ should be set to ‘one’.
For aircraft where the pressure altitude that is based on a Gillham coded input that has not been cross-checked against another source of pressure altitude, the ‘NICbaro’ should be set to ‘zero’. Otherwise, the ‘NICbaro’ should be set to ‘one’.
For general guidance on the ADS-B ‘NICbaro’ indicator that is associated with Pressure Altitude information, refer to Appendix H, Part 1, Definition 9.
(d) Vertical Rate
The Vertical Rate information should come from the most accurate and steady source.
In order to ensure that minimum performance requirements are met for Vertical Rate information, the following source prioritisation should be applied:
— Hybrid Vertical Rate Source: the information may be taken from a hybrid system which filters barometric vertical rate with an inertial reference unit (IRU) vertical rate and GNSS vertical rate, provided the accuracy of the vertical rate output is at least as good as barometric vertical rate sources (e.g. ETSO-C106).
— Blended Vertical Rate Source: the information may be taken from a blended system which filters IRU vertical rate and barometric vertical rate, provided the accuracy of the vertical rate output t is at least as good as barometric vertical rate sources (e.g. ETSO-C106).
— Barometric Vertical Rate Source: the information may be taken from an air data computer (ADC) holding an EASA equipment authorisation in accordance with ETSO-C106 or a vertical velocity instrument holding an EASA equipment authorisation in accordance with applicable revisions of ETSO-C8().
— GNSS Vertical Rate Source: GNSS vertical velocity equipment which have not been qualified in accordance with CS ACNS.D.ADSB.070 should not be interfaced with the ADS‑B transmit unit.
Vertical Rate from an inertial sensor that is not blended with barometric altitude should not be transmitted. Neither should ADS-B transmit units derive a barometric altitude rate by sampling barometric altitude measurements.
The source bit for vertical rate (1090 ES register 0916, message bit ‘36’) should be coded as barometric when utilising barometric rate from an air data computer, or when using a blended or hybrid vertical rate. The source bit for vertical rate should only be coded as geometric when using vertical rate from a GNSS source.
Note: due to differences in the respective transmit formats, the above source prioritisation differs in some parts with the guidance applicable to Mode S Enhanced Surveillance as provided in AMC1 ACNS.D.EHS.015.
For general guidance on Vertical Rate data sources, refer to Appendix H, Part 1, Definition 14.
(e) Selected altitude (and related modes)
With respect to the various status and mode fields contained in Register 6216 (Subtype 1), the respective provisions of AMC1 ACNS.D.EHS.015(c)(1) apply to the ‘Selected Altitude Type’, ‘Status of MCP/FCU Mode Bits’, ‘VNAV Mode Engaged’, ‘Altitude Hold Mode’, and ‘Approach Mode’ information.
The population of the additional Autopilot Engaged and LNAV Mode Engaged fields status bits are optional but should be populated where the data is available.
[Issue: CS-ACNS/4]
CS ACNS.D.ADSB.085 Geometric Altitude
ED Decision 2013/031/R
(See AMC1 ACNS.D.ADSB.085)
(a) Geometric Altitude is provided by the horizontal position and velocity source (see CS ACNS.D.ADSB.070).
(b) Geometric Altitude is transmitted as height above WGS-84 ellipsoid.
AMC1 ACNS.D.ADSB.085 Geometric Altitude
ED Decision 2013/031/R
(a) Geometric Altitude data source
The position source should output a vertical position accuracy metric to support the encoding of the Geometric Altitude GVA quality indicator.
GNSS position sources should provide the geometric altitude accuracy through the vertical figure of merit (VFOM). If that is the case, the vertical position source accuracy output by a GNSS receiver should have been qualified as per Appendix H Part 5 paragraph 5.
If the position source does not output a qualified vertical accuracy metric, the GVA parameter should be set to ‘zero’.
For general guidance on the GVA encoding, refer to Definition 20 in Appendix H of Subpart D.
(b) Geometric Altitude Reference
A GNSS position source compliant with CS ACNS.D.ADSB.070 provides Geometric Altitude, in its native format, as geocentric height above the earth’s ellipsoid shape. Height Above Ellipsoid (HAE) is described by the WGS-84 format.
Another altitude reference is described by the earth’s geoid, a surface on which the gravitational potential is constant and which approximates the (local) mean levels of all the earth's seas. The difference between the mathematically idealised smooth ellipsoid and irregular geoid surfaces varies between +106m to -85m across the earth. The related Mean Sea Level (MSL) altitude is then established as the sum of the HAE altitude and those local differences (using look-up tables). MSL is sometimes also referred to as Height-Above-Geoid (HAG).
A position source that only provides HAG or MSL altitude (ARINC label 076) but not HAE (ARINC label 370) should not be interfaced to the ADS-B transmit unit unless the ADS-B transmit unit can properly convert HAG/MSL to HAE, using the same HAG/MSL model as the position source (typically NATO STANAG Appendix 6). This should be based on position source installation instructions that specify a deterministic method to perform conversion to HAE, and be demonstrated during ADS-B transmit unit design approval. It is expected that the respective compliance information is supplied by the position and velocity source, and ADS-B transmit unit manufacturers through a Declaration of Design and Performance (DDP) or an equivalent document.
Note: Horizontal position sources compliant with Class 3 equipment approved under ETSO-C145c/C146c are required to output HAE altitude. The requirement has been implemented from revision C of RTCA/DO-229 onwards.
(c) Geometric Altitude Accuracy Quality Indicator Testing
If a qualified vertical accuracy metric is available, under nominal GNSS satellite constellation and visibility conditions, the transmitted GVA value should be a minimum of ‘one’.