2.
A stable TTG must be obtained prior to generating intent messages for TC reporting. A TTG value is considered “stable” if the estimated TTG, based on past information, is consistent with the current TTG value, i.e. the difference between the estimated and current TTG value is less than some threshold value. Specific rules for TTG stability will be determined during TC report format validation testing.
Figure 8 and the associated tables (7a and 7b) show one application of these conditions and the command/planned logic described in Section 6. In this example, the aircraft flies a 030 heading to intercept a lateral FMS path (TCP #1) consisting of waypoints ABC (TCP #2) and DEF (TCP #4). The aircraft also climbs at constant vertical speed and levels off at FL210 (TCP #3). Tables 7a and 7b show TC reports for Figure 8 provided by a fully equipped aircraft (able to support all DO-242A elements) and one considered to represent an early (partially equipped) glass cockpit aircraft, respectfully.
The fully equipped aircraft (Table 7a) provides FMS estimates for the latitude and longitude at the intercept point and MCP level off. Altitude estimates are provided at waypoints ABC and DEF. Since heading legs are not supported in ARINC 702A, the track to path intercept must be estimated using the current track. The aircraft will join the planned path with a fly-by turn.
Path Intercept Point
ABC 090 Track Level off at FL210
12
030 Heading
3
DEF
120 Track
Conditional Waypoint
Constant Heading Segment FMS Flight Plan FMS Waypoint 1-4: TCP Numbers
Figure 8. Constant Vertical Speed Climb and Constant Heading to Intercept an FMS Flight Plan
Table 7a. Trajectory Change Report Elements for Figure 8 (Fully Equipped Aircraft)
# Contents TC+0 Report Values (TCP 1) TC+1 Report Values (TCP 2) TC+2 Report Values (TCP 3) TC+3 Report Values (TCP 4)
4 TC Sequence Number 0 1 2 3
5a TC Cycle Number 0 0 0 0
5b (Reserved) * * * *
6 Time to Go (TTG) TTG-Intercept TTG-ABC TTG-MCP_ALT TTG-DEF
7a Data Available and TC Type (Horiz) Fly-by TF and Fly-by Course to Fix TF and Fly-by
7b TC Latitude Estimate LatitudeABC Estimate LatitudeDEF
7c TC Longitude Estimate LongitudeABC Estimate LongitudeDEF
7d Turn Radius Intercept Radius RadiusABC X RadiusDEF
7e Track to TCP Current Track 090 120 120
7f Track from TCP 090 120 X Track from DEF
7g (Reserved) * * * *
7h Command/Planned (Horizontal) Command Command Command Command
8a Data Available and TC Type (Vertical) Estimate Estimate Target Altitude Target Altitude
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