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higher ones (e.g. NUC=7 or NAC=7). Such deviation from the above target requirement
need to be listed in the Aircraft Flight Manual (refer to Section 9.3).
8.3.4 The value of the horizontal position quality indicators need to be based on the
integrity information for the encoding of the ED-102/DO-260 related NUC and the DO-
260A related NIC quality indicator, as related to the horizontal position sources.
In addition, the encoding of the DO-260A NAC quality indicator needs to be based on the
accuracy information of the horizontal position sources.
8.3.5 In case of ED-102/DO-260 based ADS-B transmit systems, the NUC Quality
Indicator value need to be encoded based on the integrity containment radius6 only.
Permissible deviation for initial implementations:
For initial implementations, some GNSS position source based aircraft installations may
encode the NUC Quality Indicator on accuracy quality information (HFOM) under rare
satellite constellation circumstances leading to the temporary unavailability of the
integrity monitoring (RAIM) function (i.e. unavailability of integrity containment radius
calculation). Such deviation from the above target requirement need to be listed in the
Aircraft Flight Manual (refer to Section 9.3).
8.3.6 If the ADS-B transmit system does not have a means to determine an
appropriate integrity containment radius and a valid position is reported, then the
Quality Indicator (i.e. NUC or NIC) need to be encoded to indicate that the integrity
containment radius is unknown (i.e. NUC/NIC should be set to ‘zero’).
8.3.7 Transmitter antenna installation needs to comply with guidance for installation
of ATC transponders to ensure satisfactory functioning. (Also refer to ED-73B)
5 This is a consequence of the definition of the quality indicator encoding describing an interval of
values between a lower and an upper bound (refer also to Appendix 4.2). For instance, a NUC=5
encoding expresses an upper bound of position accuracy quality indication of 0.3NM whilst a
NUC=7 encoding expresses an upper bound of 0.05NM. Therefore, in case of e.g. the actual
GNSS position source performance, a NUC=5 encoding provides sufficient margin to also
correctly express the effects of on-board uncompensated latency whilst this is not the case for a
NUC=7 encoding any more.
6 I.e. GNSS conformant HPL/HIL information.
6(21)
AMC 20-24 Effective: 02/05/2008
Annex II to ED Decision 2008/004/R of 25/04/2008
8.3.8 If more than one ADS-B transmit system is installed, simultaneous operation of
both transmit systems needs to be prevented.
8.4 Horizontal Position Data Sources
8.4.1 The requirements on horizontal position data sources are based on the ED-126
safety and performance assessments.
8.4.2 Components of horizontal position data sources external to the aircraft ADS-B
system (such as the GNSS space segment) fall outside these airworthiness
considerations. Such external components are assumed to operate in accordance with
their specified nominal performance7.
Nevertheless, failures of the external data source components are required to be
detected through on-board monitoring (as expressed in section 8.4.3).
8.4.3 Any eligible horizontal position data source needs to meet the following
minimum requirements (refer also to Table 2 in Appendix 3):
• Correct encoding of quality indicator information in line with the actual performance
of the selected horizontal position data source(s), i.e. in relation to position integrity
containment bound (ED-102/DO-260 and DO-260A ADS-B transmit systems) and
position accuracy (DO-260A ADS-B transmit systems);
• Position source failure probability: 10-4 per hour8;
• Position integrity alert failure probability, commensurate with the performance
characteristics of GNSS integrity monitoring9: 10-3 (per position source failure
event);
• Position integrity time to alert: 10 seconds.
8.4.4 If available and valid, integrity containment radius information should be
provided to the ADS-B transmit system from the position data source, or equivalent, on
the same interface as and together with each positional data.
8.4.5 If the integrity containment radius is not provided by the horizontal position
data source, the ADS-B transmit system may use other means to establish an
appropriate integrity containment radius10, provided a requirements compliant integrity
alert mechanism is available.
8.4.6 Use of GNSS Systems as Primary Position Data Source
8.4.6.1 GNSS is considered as primary horizontal position data source for the provision
of an acceptable accuracy and integrity performance in support of the ATC separation
services contained within the ADS-B-NRA application.
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