Home' RTCA Documents for Review : C2 Link Systems MASPS_Draft Contents Appendix D
© 2018 RTCA, Inc.
Depending on the situation these transactions can consist of one or many information
To assist in assessing the values of the RLTP parameters , the use cases described in
B.6.2.6and B.6.3.6 were used as a means to develop sequences of events and associated
timelines. Using those aspects, the “amount of time” was calculated that could be allowed
for these transactions to be completed before some significant reduction in either efficiency
or safety occurred. This MASPS uses the DO-264  term Transaction Expiration Time
(TET) for that “amount of time”; including situations where the transaction is only one
Note D-1: Although TET will have an influence on the time at which a Lost C2 Link state
will need to be declared, other operational considerations, such as airspace
traffic density, will also need to be taken into account before a Lost C2 Link
Decision Time should be defined. Defining these operational considerations
as well as when a Lost C2 Link state should be declared are beyond the scope
of this MASPS.
This MASPS also uses the concept of C2 Link System interruptions which are defined as:
Temporary situations where the C2 Link System is unavailable,
discontinuous, introduces too much delay or lacks integrity.
Notably, this definition includes all reasons (not just unavailability) for why information
intended to be exchanged will be unusable by the recipient and consequently information
exchanges will be interrupted. Interruptions are therefore the only driver of the C2 Link
System’s RLTP and the reason why transactions may not be completed in a timely manner.
Note D-2: Since the consequences of interruptions may eventually be a declaration of a
Lost C2 Link state, it is important that there is a minimization of nuisance
declarations while balancing the safety risk of not declaring a Lost C2 Link
state soon enough.
During the development of the OPA, it was recognized that there were two categories of
C2 Link System interruptions; short and long. Interruptions that are short, compared to the
transaction time, typically affect airspace operating efficiency whereas interruptions that
are long, compared to the transaction time, may affect airspace safety. The performance
metrics in the subsequent sections of this Appendix recognize this categorization.
In addition to TET, these assessments also include derivation of the Availability,
Continuity, Integrity and the allowable one-way Latency through the C2 Link System. This
MASPS uses the DO-264  definitions of Availability, Continuity and Integrity, repeated
here for reference, namely:
Availability (of Service) - The probability that the communications system
between the two parties1 is in service when needed.
Note D-3: In the subsequent Subsections of this Appendix, Availability is calculated using
the following three steps:
Step 1. The probability that an interruption can be allowed to occur during actual use
is calculated by dividing the interruption time by the total time of actual use. The latter
is the sum of the interruption time and the average time for a single actual individual
use or a single transaction/exchange multiplied by the number of transactions that are
required to meet the Allowable Quantitative Probability (see Table E-1).
1 Here the parties are the UA and the CS.
Links Archive DO-XYZ_ED-ABC_FRAC_SC236_MASPS Navigation Previous Page Next Page