Minimum Aviation System Performance Standards for Aircraft ...

. For ADS-B systems that use segmented messages for SV data, time-critical SV report
elements that are not updated in the current received message shall (242AR3.56) be
estimated whenever the SV report is updated. The time-critical SV elements are
defined as the following:
i. Geometric position (latitude, longitude, geometric height, and their validity
flags – elements 4a, 4b, 4c, 5a, 5b);
ii. Horizontal velocity and horizontal velocity validity (elements 6a, 6b, 6c, 7a,
7b);
iii. Heading while on the surface (elements 8a, 8b);
iv. Pressure altitude (elements 9a, 9b);
v. Vertical rate (elements 10a, 10b); and
vi. NIC (element 11).
Note 1: Estimation of NIC is done by simply retaining the last reported value.
c. For time-critical elements of the SV report, a ADS-B receiving subsystem’s report
assembly function shall (242AR3.57) indicate “no data available” if no data are
received in the preceding coast interval specified in Table 3.4.3.3.1.1a (§3.4.3.3.1.1).
Note 2: An ADS-B receiving subsystem may mark data elements as “no data
available” by setting the associated validity bit(s) to ZERO. For NIC this
is done by setting the value of NIC to ZERO.
3.5.1.3.3 Time of Applicability (TOA) Field for SV Report
The Time of Applicability (TOA) field in the SV report describes the time at which the
elements of that report are valid.
Note: As mentioned in the definition of latency in §3.4.3.3.2.1, the times of applicability
of position and velocity may differ. The TOA field in the SV report contains the
time of applicability of position.
The time of applicability (TOA) relative to local system time shall (242AR3.58) be
updated with each State Vector report update.
Requirements on the accuracy of the TOA field in the SV report are given in §3.4.3.3.2.2,
and may be paraphrased as follows:
a. The standard deviation of the SV report time error is to be less than 0.5 s.
b. The mean report time error for the position elements of the SV report is not to exceed
0.5 s.
c. The mean report time error for the velocity elements of the SV report is not to exceed
1.5 s.
© 20xx, RTCA, Inc.