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is designated for Xo processing. The intruder is invalid for TRM processing. An intruder with
this degraded surveillance setting must be omitted from the inputs to INTRUDERPREP. For
that reason, this value for degraded_surveillance is not called out in the conditional.
When the surveillance quality is adequate for producing both RAs and TAs, the ownship ACAS-X
operational mode setting (input_own.opmode) is used to determine the type of TRM processing to
be used for the intruder as follows:
• When input_own.opmode is OPMODE_RA, own aircraft is in ACAS-X TA/RA operational
mode. st_int.processing is set to RA_PROCESSING_GLOBAL_TARA. If the previous cycle
used degraded surveillance processing for this intruder, both the coordination delay counter
and the initialization counter are reset (reset_cost_state is TRUE). If the previous cycle used
Global TA-Only processing for all intruders, only the coordination delay counter is reset. The
intialization counter continues to reflect the amount of time the intruder track has had a chance
to stablilize for use in the TRM. Resetting the coordination delay counter delays output of a
VRC to this intruder to allow time for receipt of a VRC from this intruder. Otherwise, there is
no reset of the online cost state in this algorithm. In the case of an intruder that was invalid on
the previous cycle, the entire intruder online cost state would have been reset on the previous
• When input_own.opmode is OPMODE_TA, own aircraft is in ACAS-X TA-Only operational
mode. st_int.processing is set to RA_PROCESSING_GLOBAL_TA_Only. The advisory state
was partially reset on the previous cycle. Neither the coordination delay counter nor the ini-
tialization delay counter are reset (reset_cost_state remains FALSE) so RAs will be produced
for conversion to TAs. Since the processing mode is RA_PROCESSING_GLOBAL_TA_Only,
no VRCs will be output to any intruder.
• When input_own.opmode is OPMODE_STANDBY, own aircraft is in Standby ACAS-X oper-
ational mode. In Standby mode, proximity advisories can be produced, but no RAs or TAs are
produced. When ownship is in Standby ACAS-X operational mode, all intruders are invalid
for vertical TRM processing. All intruders must be omitted from inputs to INTRUDERPREP.
As a result, input_own.opmode will never be set to OPMODE_STANDBY in this algorithm.
For that reason, this setting is not called out in the conditional.
Next, the values to be used for the intruder altitude (z_int_ave) and vertical rate (dz_int_ave) are
determined by taking the weighted mean of the vertical beliefs for each of those values.
In the second conditional block, the selected protection mode is checked and validated. A change
of protection mode is allowed only if there is either no active resolution advisory or Global TA-only
processing is in effect. Any rules regarding use of Designated No Alerts (DNA) with a specific
protection mode are enforced by the STM.
The values of the current protection mode (st_int.protection_mode_curr), protection mode index
(mode_int), whether the intruder is excluded from determination of the global RA (exclude_int),
and the online cost state are set based on the results of the processing above.
mode_int is an array index used throughout the TRM to retrieve either Xa or Xo CSPO-3000 pa-
rameters for use. The GETPROTECTIONMODEINDEX helper algorithm returns the index into the
parameter array params().modes. The value of protect_mode_int must be validated prior to running
the TRM. exclude_int is set to TRUE when the intruder is marked as having certain types of degraded
The values of the designated mode state variable (st_int.designated_mode), whether the intruder
ACAS Xa/Xo MOPS, Vol. II
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