Home' RTCA Documents for Review : ACAS X MOPS DRAFT Vol. 2 Contents DRAFT
may not be available at the flight deck for undesignation.
Once the information in the report has been adjusted for validity, the information in the target
database must be updated. The second part of ADJUSTTARGETDESIGNATIONVALIDITY updates
the designation state for each Target in the database. In the case where a designated Target has been
dropped, a special TRMINTRUDERINPUT is added to the report.
Whenever the Target was omitted from the output to the TRM, information in the target database
requires updating. Reasons for the Target being omitted from the output include:
1. The Target track was dropped
2. The Target was filtered from the outputs to the TRM
3. AddTracksToReport was not called (designation_needs_update is true)
Omission of a Target from the output to the TRM is indicated by setting DESIGNATIONSTATE valid
to false and was_dropped to true. In addition, when the Target is designated, the following actions
• The DESIGNATIONSTATE timers are updated, if they wouldn’t have been updated previously
• The DESIGNATIONSTATE ground history (r_ground_history) is updated, if it wouldn’t have
been updated previously
• The DESIGNATIONSTATE status is updated, if the status information didn’t indicate undesig-
• A special invalid intruder, with the degraded surveillance bits set to DEGRADED_SURVEIL-
LANCE_ALL, is added to the output to the TRM
The ASSAP function will undesignate designated traffic when it is no longer marked as valid. In
ACAS, designation on the Target is maintained for a period of time after all tracks on the Target
are lost and the Target would otherwise be considered "dropped". To prevent the ASSAP function
from undesignating this dropped Target, the ACAS intruder output to the ASSAP function must
include designation information for that Target. The special invalid intruder is used to achieve this
objective. The DROPPEDINTRUDERSADJUSTMENT algorithm in the TRM uses the TRMINTRUD-
ERINPUT designated mode, validity, and status information in the special invalid intruder to produce
designation outputs for dropped targets that will prevent the ASSAP function from undesignating
As mentioned above, when a designated Target has been dropped or filtered from the output, it is
no longer displayed and is no longer available for undesignation at the flight deck. In this case,
it becomes necessary to allow designation of another Target while the designated Target is hidden.
When a new Target is designated, the hidden designated Target is undesignated and that information
will be output to the TRM. When the designation timer expires on the hidden designated Target, it
will be undesignated and that information will be output to the TRM. While its designation timer
is running and no other targets are designated in its place, the hidden designated Target remains
designated and valid in the TRM designation output to the ASSAP function.
Whenever the Target is included in the original output to the TRM, the Target was not dropped.
That condition is indicated by setting was_dropped in the DESIGNATIONSTATE to false. When the
Target is not designated and N_targets_limit has been reached, the DESIGNATIONSTATE valid flags
are reset to false. Otherwise, the DESIGNATIONSTATE timers are reset to 0 when target designation
ACAS Xa/Xo MOPS, Vol. II
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