Automatic Dependent Surveillance(12)

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Separation assurance applications will likely emphasize the command trajectory when predicting and resolving traffic conflicts. In some cases, the planned trajectory may be valuable for situation awareness when a change to the command trajectory is anticipated. This situation may be common in cases where the aircraft is flying a published arrival route. Consider the example shown in Figure 5b. The aircraft flies along a lateral and vertical FMS path containing a waypoint altitude constraint (XYZ) between the top and end of descent points. Following a common procedure, the flight crew sets the MCP Selected Altitude to the altitude constraint at XYZ (15,000 ft). Without further pilot input, the aircraft will remain level at 15,000 ft after passing XYZ. This path defines the command trajectory. In order to stay on the FMS descent path, the crew must reset the MCP selected altitude below 15,000 ft prior to reaching XYZ. If the crew intends to continue on the vertical FMS descent path, the command trajectory may not reflect the crew’s long-term intentions. Separation assurance and flow management applications may benefit by considering both command and planned trajectory information.
Constant 090 Track throughout Descent
Figure 5b. FMS Descent with MCP/FCU Selected Altitude = FMS Target Altitude
The receiving system can use the horizontal and vertical command/planned flags in the TC report described below to determine whether a broadcast TCP is part of the aircraft’s command or planned trajectory.

7 Trajectory Change (TC) Reports

Trajectory Change reports replace the TCPs defined in DO-242. They provide an expandable structure capable of describing TCPs, waypoint constraints, and the flight segments that connect them. One TC report is provided for each TCP or waypoint constraint. Many additional elements have been added to the DO-242 TCP report to facilitate path re-generation, data confidence assessment, and conformance monitoring. Some of the new parameters have been added to be consistent with ARINC trajectory bus specifications as reflected in Eurocontrol ADS Requirements.8
Table 4 shows the TC report structure. Not all elements are fully implemented in DO-242A, but are included to show planned expansion as data becomes available. TC report fields are filled based on information availability aboard the transmitting aircraft and the TC type.
Table 4. Trajectory Change Report
TC Report Element #  Contents 
ID  1  Participant Address 
2  Address Qualifier 
TOA  3  Time of Applicability 
TC Report #  4  TC Report Sequence Number 
TC Report Version  5a  TC Report Cycle Number 
5b  (Reserved for TC Management Indicator)1 
TTG  6  TimetoGo(TTG) 
Horizontal TC Report Information  7a  Horizontal Data Available and Horizontal TC Type 
7b  TC Latitude 
7c  TC Longitude 
7d  Turn Radius 
7e  Track to TCP 
7f  Track from TCP 
7g  (Reserved for Horizontal Conformance Flag)1 
7h  Horizontal Command/Planned Flag 
Vertical TC Report Information  8a  Vertical Data Available and Vertical TC Type 
8b  TC Altitude2 
8c  TC Altitude Type 
8d  (Reserved for Altitude Constraint Type)1 
8e  (Reserved for Able/Unable Altitude Constraint)1 
8f  (Reserved for Vertical Conformance Flag)1 
8g  Vertical Command/Planned Flag 

1Only applies to active flight segment.
2Altitude estimate or altitude target, e.g. cruise altitude.

The first three elements of the TC report: Participant Address, Address Qualifier and Time of Applicability are common to all ADS-B reports. Time of applicability and Time to Go (TTG) are updated each time a TC report is output. See Section 11 for a discussion of TC report “refreshment” when TC report intent information is not currently received.
　
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