i.e.
TCP+0, TCP+1, TCP+2, TCP+3, respectively. TC Report Cycle Number is a 2 bit code which increments whenever a major change in TC report intent occurs, such as sequencing the current TCP. See Section 11 for a detailed explanation of TC report cycle number and TC report updating and maintenance. Space is reserved for the TC Management Indicator. This field will specify how multiple TC reports are managed when there is a major change in intent. Management of multiple TC reports is described in Section 11, but is deferred for later MASPS revisions.
All TC reports should have a unique sequence number, a common time of applicability and a common TC report cycle number at each report time. Intent data not updated within the coast time specified in Section 10 are marked ‘not available’ and are not to be used until new intent data is received.
Time to Go (TTG) is a required element for all TC reports. It indicates the remaining time to the next TCP. TTG can be added to the time of applicability to determine the estimated time of arrival at the TCP.
Horizontal and Vertical Data Availability status is combined with the respective Horizontal and Vertical TC Type fields. If these fields are non-zero, then horizontal and vertical trajectory change information is being reported and those reports are filled with currently relevant information. (Note: if TC report intent data is not received within a specified ‘coast time’, then those data fields not recently updated are marked ‘not available’). The associated horizontal and vertical data fields should not be used if they are reported unavailable.
The TC Type fields specify the flight segment and endpoint change type. Both a horizontal and a vertical TC type are included to aid interpretation of the data elements for constructing path segments. In addition, it is feasible to have both a routing change and a vertical change or constraint at the same waypoint. The TC type fields specify the way that the data received is to be interpreted, i.e. which elements are required for constructing the flight segment and endpoint conditions. Example TC types are fly-by waypoint, direct-to-fix, and RF leg (lateral cases) and top of climb, top of descent, and target altitude (vertical cases). Section 8 describes the TC types included in DO-242A. Other types, including waypoint constraints, may be added to future revisions.
The availability of TC Latitude and TC Longitude data depends on the transmitting aircraft’s operating mode and equipment capability. These elements are provided if they are associated with a known waypoint or can be estimated by the FMS. These elements will have varying accuracy depending on TC type. When using FMS lateral and vertical navigation, TCPs associated with waypoints can be estimated with high confidence. For TCPs which do not involve closed-loop control, such as top of climb, top of descent, or path intercepts, the latitude, longitude and time elements have higher uncertainty. Low integrity latitude/longitude predictions such as the “green arc” on Boeing aircraft that predicts altitude level-offs for MCP modes are not required, but TTG is required for any vertical TCP. These predictions can vary greatly if they do not compensate for wind and aircraft performance.
Figures 6 and 7 show the information needed for fixed radius and fly-by turns (Track to TCP, Track from TCP, and Turn Radius). Fixed radius turns include turn radius and start and end of turn points. Fly-by turns can also be described in this manner, however the alternate representation in Figure 7 is acceptable if the aircraft cannot provide start and end of turn points. In this case, the fly-by turn waypoint is provided, along with the track to and track from that point and the turn radius. Fly-over turns are represented in DO-242A as a Direct-to or Course-to transition to the specified endpoint. For other horizontal TCPs, only the track to the TCP is provided.
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