Waypoint
(TCP+1)
(TCP)
Track to TCP
Track from TCP
Track to TCP
Track from TCP+1
Turn Points
Turn Radius
Figure 6. Fixed Radius or Fly-by Turn Figure 7. Fly-by Turn
Space is reserved for Horizontal and Vertical Conformance validity. These flags assess the conformance of the transmitting aircraft to its broadcast path. It is anticipated that future revisions may use horizontal and vertical RNP bounds to specify trajectory conformance. The conformance flags would broadcast the ability of the aircraft to conform to the specified trajectory bounds. For non-RNP aircraft, other measures of conformance may be specified.
The Horizontal and Vertical Command/Planned Flags delimit whether the flight segment and TCP is part of the command or planned trajectory (see description in Section 6). Successive TCPs or altitude constraint points that are part of the command trajectory should be ordered as they are expected to occur, i.e. by TTG. In cases where time to go cannot be determined, no TC report is generated. If there is space available for additional points, planned TCPs can be included, but they should be placed at the end of the TCP list.
TC altitude fields include TC Altitude, TC Altitude Type, Reserved for Altitude Constraint Type, and Reserved for Able/Unable Altitude Constraint. TC Altitude is the estimated or constraint altitude at the TCP, depending on vertical TC type. TC Altitude Type specifies whether the TCP altitude is referenced to MSL or Flight Level. The Altitude Constraint Type and Able/Unable Altitude Constraint are provisioned for future use. These elements can be used to indicate the type of altitude constraint (“At”, “At or Above”, “At or Below”) and the transmitting aircraft’s assessment of its ability to meet the altitude constraint. Altitude constraints may or may not be associated with a trajectory level off, since the aircraft may be able to comply with the constraint without changing its trajectory. In the case that “window” constraints are specified, i.e. both “At or Above” and “At or Below” altitudes are specified; only one window constraint is reported. (See Section 8.) Future DO-242 revisions may further expand TC reports to include speed and time constraints. NASA’s AATT program is currently investigating autonomous flight operations in a constrained environment, such as those that may occur just outside a terminal area.7 These restrictions could include combinations of speed, altitude, and time constraints. Note that the “able / unable” altitude constraint flag is different than the vertical conformance flag since the former applies at a single point and the latter to an entire vertical segment.
Figures 4 and 5 (5a and 5b) are examples of horizontal and vertical FMS trajectories, respectively. The filled TC report elements corresponding to Figures 4 and 5a are given in Tables 5 and 6, respectively. Note that DO-242A does not support multiple TC reports. Both of these examples show how the TC reports would be filled for fully equipped aircraft able to support each element implemented in DO-242A. It is expected that many current aircraft will not have these full capabilities, however these examples are provided in order to illustrate the application of a wide range of DO-242A data elements. Figure 8 shows a more complex trajectory involving MCP/FCU and FMS targets. Tables 7a and 7b offer a comparison of TC reports for Figure 8 provided by fully and partially equipped aircraft, respectfully.
Figure 4 shows an aircraft turning to join a 040 course to waypoint ABC, followed by two routing changes at DEF and GHI. The rollout point is not considered to be a TCP, since the intended path is a Course-to-ABC segment. After rolling out, it will join the FMS flight plan and fly to waypoints DEF and GHI. This example is flown at a constant altitude of 15,000 ft. All latitude and longitude fields are filled since all TCPs in this example are FMS waypoints. The aircraft is holding its selected 15,000 ft altitude, which is repeated for each TCP. The end of the CF segment is the start of the Fly-By Turn, which is represented implicitly by the ABC waypoint and Fly-By turn radius. (In effect, the Fly-By Turn TC report implicitly represents both the CF track-to ABC segment and the Fly-By Turn at ABC to the next TF segment.) The straight line and turn segments for the other Fly-By turns are similarly represented implicitly, reducing the number of TC reports to represent the intended path.
　
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