Table 2. Target State Report Elements for Figure 3
TS Report Element # Contents Example Values
Horizontal 4a Horizontal Data Available and Horizontal Target Source Indicator MCP Selected Heading
Short 4b Target Heading or Track Angle 090 deg
Term 4c Target Heading/Track Indicator Target Heading
Intent 4e Horizontal Mode Indicator Capturing/ Maintaining
Vertical 5a Vertical Data Available and Vertical Target Source Indicator MCP Selected Altitude
Short 5b Target Altitude 8,000 ft
Term 5c Target Altitude Type MSL
Intent 5d Target Altitude Capability Full Capability
5e Vertical Mode Indicator Acquiring
In another example, the aircraft in Figure 4 is turning to join a 040 course (track) to the ABC waypoint. It is holding its current altitude (15,000 ft). TS report values are provided in Table 3. The target source indicators show that the target track comes from the FMS, while the target altitude is the MCP selected altitude. Horizontal and vertical target states are available and considered reliable. As shown by the mode indicators, the aircraft is acquiring the horizontal target and maintaining the vertical target. Mode indicators show that horizontal and vertical target information is available.
Target Altitude (15,000 ft)
ABC DEF
GHI
Figure 4. Intercept Course to FMS Flight Plan at Constant Altitude Table 3. Target State Report Elements for Figure 4
TS Report Element # Contents Example Values
Horizontal 4a Horizontal Data Available and Horizontal Target Source Indicator FMS/RNAV
Short 4b Target Heading or Track Angle 040 deg
Term Intent 4c Target Heading/Track Indicator Target Track Angle
4e Horizontal Mode Indicator Acquiring
Vertical Short Term Intent 5a Vertical Data Available and Vertical Target Source Indicator MCP Selected Altitude
5b Target Altitude 15,000 ft
5c Target Altitude Type MSL
5d Target Altitude Capability Full Capability
5e Vertical Mode Indicator Capturing/ Maintaining
5 Trajectory Change Point (TCP) Definition
Further investigation into the many types of TCPs that can occur along an operational trajectory has led to a revised TCP definition for DO-242A. The new definition accommodates TCPs that do not occur at a known 3D position in space. Many flight segment changes occur when certain trajectory conditions are met, rather than at defined points in space. For example, an aircraft may be climbing in a constant vertical speed mode towards a target altitude (Figure 3). In this case, the condition for changing trajectory is based on capturing the target altitude and not on arrival at a defined point. The predicted location accuracy of these TC types may depend on unknown wind conditions and changing aircraft performance. An analogous lateral situation may occur when an aircraft flies at constant heading to intercept a flight plan route (see Figure 8). In this case, the first TCP occurs when intercepting the track to the next FMS/RNAV waypoint. The intercept location is also dependent on wind parameters that may not be accurately known.
The following TCP definition has been adopted to accommodate prediction uncertainties: “A trajectory change point (TCP) is a point where an anticipated change in the aircraft’s velocity vector will cause an intended change in trajectory.” The change in trajectory may be either a change in path or a change in speed. Examples of TCPs under this definition include 2-D routing changes, the start and end points of a specified turn transition, FMS predicted Top of Climb and Top of Descent points, and target altitudes such as MCP selected altitude when currently in climb or descent transitions. A full list of TC types included in DO-242A is provided in Section 8. Future revisions may add additional TC types that meet this definition.
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