Home' RTCA Documents for Review : C2 Link Systems MASPS_Draft Contents Appendix E
© 2018 RTCA, Inc.
During the entire flight, the C2 Link Management System in the CS uplinks telecommands
received from other CS systems to the UA and the C2 Link Management System on the
UA downlinks telemetry received from other systems on the UA to the CS over the C2
Link System. During the takeoff and climb-out operations, there should be no Scheduled
Switchovers because of the increased risk of a Lost C2 Link occurring during the dynamic
operations that normally occur in this phase of operations.
During the cruise and aerial work phase of the flight, the QoSD of the link varies over time
due to, for example, UA maneuvers, weather, and terrain obstruction. Consequently, there
may be interruptions on the C2 Link System’s ability to maintain its support of information
exchange. These interruptions are monitored by the CS and UA, based on status reports
from the C2 Link Management Systems, and decisions made, external to the C2 Link
System, about performing Unscheduled Switchovers or Lost C2 Link declarations.
Additionally, the C2 Link Management System may perform low-level physical layer
actions, such as resynchronization, to recover from these interruptions.
Switchover Initiation and Execution:
During the cruise and aerial work phase of the flight, whether scheduled or unscheduled,
the pilot will be able to initiate a Switchover from the currently used link to the link that
will be used for the next segment of the flight. This is accomplished by the remote pilot
first determining if the next planned link is in service then commanding the CS C2 Link
Management System to initiate execution of the Switchover. During this process, the CS
and UA C2 Link Management Systems execute a sequence of actions, including the
exchange of Control Messages to carry out the Switchover.
For a Make-before-Break (MbB) Switchover, the CS and UA C2 Link Management
Systems continue sending User Data over the current link while the Switchover is being
executed and the flow of User Data only starts to flow over the new link after the
Switchover has been completed. The QoSD for the newly established link is determined
before the Switchover to ensure the new link has acceptable QoSD for the Required Link
Technical Performance (RLTP) before stopping the flow of User Data over the original
link and then terminating that C2 Link System Connection. If the QoSD of the new link
does not meet the minimum requirements, the MbB Switchover is aborted, data flow over
the original link C2 Link System Connection is maintained, and UA and CS external
systems are notified so they can take appropriate action.
In a Break-before-Make (BbM) Switchover, the Connection over the current link is
terminated which will stop User Data flow over that Connection. Then the execution of
the Switchover to the new link is performed. User Data then begins to be sent. The QoSD
of that new link is evaluated after the Switchover is completed and the QoSD of the new
link is reported to the CS and UA. However, if the QoSD does not meet the minimum
requirements, the UA and CS external systems are notified so they can take appropriate
If the MbB or BbM Switchovers fail to be completed, the UA and CS C2 Link Management
Systems will perform the preprogrammed actions (i.e., actions programmed into the UA in
the pre-flight phase as part of the flight planning process) required by the UAS operating
restrictions established during the airworthiness certification process. These actions could
include automatic attempts to establish connectivity through the original link, the new link
or an alternate link, or the UAS executing the Lost C2 Link procedures.
Links Archive DO-XYZ_ED-ABC_FRAC_SC236_MASPS Navigation Previous Page Next Page