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TTG is originally computed from ETA or estimated time of arrival at a waypoint as the time difference between the ETA point and the estimated time of applicability for ADS-B broadcasting. When TCP message data with TTG is received, coast time is set to zero, and TTG is referenced relative to the report time of applicability. If no further messages for that TCP are received at the next report time, then coast time is incremented and TTG is decremented by delta time of applicability, i.e. the report time, coast time and TTG are all updated relative to the current time of applicability. This process of TC data ‘refreshment’ continues until an updated TCP message with TTG is received, the coast time exceeds the coast interval threshold for data renewal causing the TC report data to be marked “not available”, or the TC report is sequenced.

11.2 TC Report Management for Future Level A3 Systems
Report management for Level A3 ADS-B systems may be accomplished by means of the TC cycle number and the TC management indicator. A change in the TC cycle number means that a major change in intent has occurred which will require a reissue of one or more TC reports, or a re-sequencing of previously issued TC reports. The TC management indicator provides information for the ADS-B report assembly function as to what actions need to be done for each previously managed TC report, i.e. whether to maintain and refresh that report, whether to re-sequence that report, or whether to mark that report as unavailable until a new TC report replaces the currently invalid intent data. This section describes report management for multiple TC reports as currently envisioned for future versions of the ADS-B MASPS.
The TC Management Indicator (TCMI) is a 3-bit field communicated in messages supporting a TC+0 report and indicates the disposition of all current TC reports when an incremented TC cycle number is detected in any such report. The currently defined values of the TC management indicator are shown in Table 9. The indicator values 0 to 2 are required for any Level A3 system, whereas the values 3 to 5 provide optional capability to minimize the rebroadcast of current TC reports upon detection of a major change in intent. Additional capabilities may be desired for standardization in future MASPS, e.g. a special value could be used to convey a “Direct to” re-sequencing of TC reports which bypasses one or more of the current TC reports.
Table 9. Trajectory Change Management Indicator (TCMI) Values
TC Management Indicator  TC Report Management Functions Following Receipt of an Updated TC Cycle Number 
0  Maintain and refresh all currently valid TC reports. 
1  Forward sequence all current TC reports (TC+1 → TC+0, etc.). 
2  Mark all currently received TC reports invalid. 
3  Maintain current TC+0 report; Mark all subsequent TC+n reports invalid 
4  Mark current TC+0 report invalid; Maintain all subsequent TC+n reports. 
5  Backward sequence all current TC reports (TC+0 → TC+1, etc.). 
6,7  Reserved for future indicator definition. 

Upon determination of a newly issued TC cycle number, the report assembly function should perform all sequencing and updating of current TC reports, as indicated by the TC management indicator. A TCMI value of zero indicates that all TC reports that are valid should be updated with TC cycle number, and have times updated to the current time of applicability. Normally, the TCMI will have a non-zero value to indicate additional actions to be performed on current TC reports. After the report assembly has performed the actions signaled by the TCMI on all updated TC reports, the TC management indicator should be reset to zero in TC+0 to indicate completion of those tasks. Once the TCMI is set to zero, any TC report data obtained during the current data broadcast can be used to update current TC reports or to initiate new TC reports. A TCMI value of one indicates that the currently active flight segment reported by TC+0 has been sequenced. This value is required in order to maintain continuity of intent after the current flight segment is sequenced. The sequencing logic is: (1) if there is no currently valid TC+1 report, and the TC+0 report has a horizontal TC type which indicates a valid track from TCP, then the current TC+0 report may be maintained after TC report updating for a time interval not to exceed 2 minutes beyond the time of TCP sequencing. Otherwise, the current TC+0 report is marked as invalid; (2) if there is a currently valid TC+1 report, then the element values for TC+1 are reinitiated as the new TC+0 report with appropriate report data refreshment. Similarly, any subsequent TC+n reports are resequenced as TC reports with sequence number n-1. The current TC report with largest valid sequence number is then marked invalid since its values are contained in a resequenced TC report.
　
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