J. Displayed Parameters - Path Errors
(1)
General The FMGC computes for display on the EIS or on the MCDU, lateral references, lateral path errors, also used in the lateral control laws and leg sequencing logic, and destination distance for performances.
(2)
Lateral references
(a) Definition
The position reference parameters are as follows:
(Ref. Fig. 029, 030)
-Bearing to go: bearing to go from the current aircraft position to the leg termination point.
-Distance to go: direct distance to go from the current aircraft position to the leg termination point.
-Time to go: time to go from the current aircraft position to the leg termination point.
-Desired track: current tangent for the active leg. TIME TO GO is always the distance to go divided by the current ground speed.
NOTE : If the current leg termination is not a fixed waypoint,
____ distance to go, turn to go and bearing to go are referred to the predicted termination (altitude, VOR radial, distance to a navaid). If the current leg is a manual termination leg, only the desired track is computed.
(b) Display of positions reference parameters (Ref. Fig. 031) Bearing to go and distance are displayed on both EIS and MCDU. Time to go and desired track are only displayed on EIS.
(3) Lateral path errors
(a) Definition The FMGC computes a crosstrack error and a track angle error for control of the aircraft along the lateral path also for determination of lateral path capture and leg sequencing.
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The TRACK ANGLE ERROR is always the difference between the DESIRED TRACK and the TRUE TRACK.
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The CROSSTRACK ERROR to a course leg is the perpendicular distance to the leg. (Ref. Fig. 032)
Reference Parameters for CF Leg
Figure 029
PF Leg (Procedure Turn)
Figure 030
Reference Parameters Display
Figure 031
Lateral Path Errors on Straight or Great Circle Path
Figure 032
-The CROSSTRACK ERROR to a circular arc is the difference between the distance from the aircraft position to the turn center and the turn radius of the arc. (Ref. Fig. 033) This definition applies for all circular arcs in holding patterns (HX legs) or AF legs.
(b) Display
Only the CROSS TRACK ERROR is displayed on the Navigation
Display.
(Ref. Fig. 031)
(4)
Destination distances
(a)
Definition The FMGC computes the distance to destination (DIST TO DEST) and direct distance to destination (DIRECT DIST TO DEST). It also computes the ALONG TRACK DIST TO GO used for performance computations.
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The DIRECT DIST TO DEST is the distance along a great circle path connecting the aircraft position to the LOC capture point and then to destination runway (Ref. 22-73-00).
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The ALONG TRACK DIST TO GO is the distance along the active leg from the point where CROSSTRACK ERROR is computed to the leg termination point. (Ref. Fig. 034)
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The DIST TO DEST is a sum of the lateral leg distances in the flight plan beginning with the active leg termination and the ALONG TRACK DIST TO GO as defined above. (Ref. Fig. 034)
(b)
Display The DIST TO DEST and DIR DIST TO DEST are output for display on the MCDU. The DIST TO DEST is displayed on F-PLN page A on the MCDU, in line 6 dedicated to the destination.
(5)
Influence of transitions The lateral reference parameters defined in Para. (2) depend on the type of leg as the path errors. But only the desired track and path errors depend on the type of transition. The influence is given hereafter.
-Type I: Time to go, bearing to go, distance to go are referred to the active leg. Desired track and crosstrack errors are computed for the curved path of the transition.
Lateral Path Errors on Circular Path
Figure 033
Along Track Distance
Figure 034
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Type II: Distance to go, time to go, bearing to go, crosstrack error, desired track are all referenced to the path to be captured. For holding pattern entries, distance to go, time to go, bearing to go are referred to the holding fix. Crosstrack error and desired track are always referenced to the associated part of the entry path that guidance is currently controlling. When an entry ends in a type II transition, they are referenced to the inbound course of the leg.
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Type III: The parameters are referenced to the heading leg.
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Type IV: All parameters except crosstrack error and desired track are referenced to the next leg at the start of transition. Crosstrack error and desired track are referenced to the arc until sequencing of the arc.
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