Automatic Dependent Surveillance(9)

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Target Altitude Type indicates whether the target altitude is an MSL altitude or a flight level. It is assumed that the local transition level is known to the transmitting aircraft and that the target altitude is MSL or a flight level depending on whether the target altitude is below the transition altitude or not.
Horizontal and Vertical Data Availability status is combined with the respective Horizontal and Vertical Target Source Indicators. If these fields are non-zero, then target heading or track angle and target altitude are being reported and those reports are filled with currently relevant information. (Note: if TS report intent data is not received within a specified ‘coast time’, then those data fields not recently updated are marked ‘not available’).
The target source indicators specify the aircraft system providing the corresponding horizontal or vertical target state. Options include the FMS/RNAV, MCP or FCU selected values, or holding the aircraft’s current state. In cases where the aircraft is acquiring a target altitude common to the MCP/FCU and FMS, the vertical target source indicator should declare the target to be the latter.
Table 1. Target State Report
TS Report Element #  Contents 
ID  1  Participant Address 
2  Address Qualifier 
TOA  3  Time of Applicability 
Horizontal Short Term Intent  4a  Horizontal Data Available and Horizontal Target Source Indicator 
4b  Target Heading or Track Angle 
4c  Target Heading/Track Indicator 
4d  (Reserved for Heading/Track Capability) 
4e  Horizontal Mode Indicator 
4f  (Reserved for Horizontal Conformance) 
Vertical Short Term Intent  5a  Vertical Data Available and Vertical Target Source Indicator 
5b  Target Altitude 
5c  Target Altitude Type 
5d  Target Altitude Capability 
5e  Vertical Mode Indicator 
5f  (Reserved for Vertical Conformance) 

Horizontal and Vertical Mode Indicators provide status information on whether the aircraft is acquiring (transitioning toward) the target state or is capturing or maintaining the target. (In the vertical plane, the FMS changes mode when ‘capture’ of a target altitude occurs. There may or may not be a subsequent guidance mode change when maintaining the target altitude.) These parameters are expected to increase integrity of predicted trajectory changes and to be useful for trajectory conformance monitoring.
Space is reserved for Horizontal and Vertical Conformance validity. These bits would provide indications of pilot or autopilot conformance to target values. Conformance to vertical and horizontal target states are under consideration, but cannot be implemented in DO-242A due to data source availability issues. These bits would determine whether the aircraft is being controlled in the direction of its flight director or autopilot command. In addition, several bits are reserved in the TS report for future growth.
Consider the example shown in Figure 3. An aircraft climbs at constant vertical speed toward the MCP selected altitude of 8,000 ft while flying a constant 090 heading. TS report values for intent elements 4 and 5, implemented in DO-242A, are provided in Table 2. Both of the targets are resident in the MCP, as indicated by the target source indicators. Non-zero values in these fields indicate that the target heading and target altitude are available and considered reliable. This aircraft has the capability to fully support target altitude, as defined above. The mode indicators show that the aircraft is maintaining the target heading and is acquiring, but has not yet captured, the target altitude.
Target Altitude (8,000 ft)

Velocity Vector Target Heading (090 deg)

Figure 3. Constant Vertical Speed Climb at Constant Heading to
　
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