  The total latency (TL) in ADS-B is the difference between the true TOA of the
original position measured by the onboard GPS and the TOA in the ADS-B report
at the GS. We processed the ADS-B reports extracted from live-data recorded at
the Chicago to produce the results in this report. We observed that 99% of
aircraft in our data set were broadcasting in non-UTC coupled mode. For these
aircraft, STARS exclusively used ADS-B reports to update tracks when available.
The calculated ULs for the non-UTC coupled ADS-B reports were well within the
budget (-200 ms to +400 ms) allowed by the DO-260B MOPS. Moreover, the mean
latencies from both methods were less than +/-50 ms. The latencies obtained
from the MTPES method were observed to be in close agreement with the means
from the ATPE method. About 1% of aircraft were broadcasting in UTC coupled
mode. The reports from these aircraft were identified to have a non-compliant
link version, causing STARS to reject these reports for tracking. Moreover, the
reported position and TOA were found to be unsynchronized, which conflicts with
the MOPS requirement for UTC coupled operation.
