-
Type V: All parameters are referenced to the course leg.
K. NAV Guidance Mode
(1) NAV mode engagement conditions The NAV mode is engaged through engagement of lateral autocontrol (Ref. 22-12-00) which includes 4 various modes:
-RWY
-NAV
-LOC (capture/track) and LAND
-GO AROUND.
Only NAV mode is dealt with by the FM part.
The selectable lateral modes in en route or terminal area or in
approach (except takeoff and landing) are:
-managed control
-heading/track control
(a) managed mode This mode is armed if the pilot pushes heading/track selector knob on the Flight Control Unit (FCU). Managed control engagement depends upon whether the aircraft is within the capture zone of the active leg. This capture zone is unlimited for heading/track legs (VX or CX legs except CF leg). This means that if LAT AUTO control is armed while one of these legs is active, it is immediately engaged. For fixed path legs, the capture zone is a 1 NM wide zone around the active leg, or at the capture point which allows a comfortable F-PLN capture without overshoot. If the aircraft is within the capture zone, then autocontrol is engaged (FCU heading/track display is dashed). Else, the previously selected HDG/TRK remains displayed and modifiable on the FCU until autocontrol is engaged. Note that performing a DIR TO revision engages NAV if it was not active. In this case, if the track corresponding to the selected heading/track intercepts the F-PLN before the TO waypoint, the F-PLN becomes as shown in the following figure. (Ref. Fig. 035) Else the flight plan remains as original. (Ref. Fig. 036) When managed control is active, the aircraft flies the flight plan as defined by the displays on the MCDU and on the ND (except when LOC mode is active). The managed control engagement state is checked each time one of the following events occurs:
-managed control is selected via the FCU
-
a F-PLN change occurs which affects the active leg
-
a parallel offset is entered or cancelled.
NAV Engagement
Figure 035
NAV Engagement Display
Figure 036
If the managed lateral control is de-activated, the control reverts to heading/track control and the heading or track is synchronized with the current one before loss of the managed control.
(b) Selected control Heading/track is engaged if the pilot chooses a target by means of the heading/ track selector knob and pulls the knob. The FCU displays the selected heading or track. Selection of heading or track mode is done via the HDGV/S-TRK FPA pushbutton switch on the FCU. In heading/track mode, the flight plan remains active without modification. On ND, the flight plan becomes dashed. Leg sequencing is automatic as if managed lateral control remained active.
(2) En route and terminal area guidance submodes The various guidance modes in these areas are:
-lateral path for geographical path legs
-heading for heading legs
-track for course legs.
(a)
Lateral path, heading, track modes These 3 modes may be selected when managed lateral control is active. The selection of the submode is determined according to the leg type of the active leg or the transition. If the active leg is a heading leg (VX legs) the heading submode is requested. If the active leg is a course leg (CX legs except CF leg) the track submode is requested. If the active leg is not a heading leg or a course leg (except CF leg) the lateral path submode is requested. This mode is de-activated if one of the following events occurs:
-managed lateral control is lost
-active leg is VX or CX leg (except CF leg)
-LOC or APPR mode is engaged
-ACTIVE primary flight plan is lost.
(b)
NAV control law parameters When NAV is engaged, the lateral control law is used to provide control to the legs (Ref. 22-71-00) and the transitions. The control law uses parameters such as crosstrack error, track angle error, desired track, nominal bank angle (as a function of ground speed).
1_ If the active leg is a course leg (CX except CF leg), the desired track is generated and the system holds this track (track control law).
2_ If the active leg is a heading leg (VX legs), the desired heading is generated and the system holds this heading (heading control law).
3_ In lateral path-mode, the bank angle command is generated by comparing the current A/C state vector (position, ground speed, track) to the desired lateral path. - For circular arc (AF), the turn control law maintains a constant radius using the nominal bank angle. There may be a correction based upon track angle error and crosstrack error.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：A320飞机维护手册 AMM AUTO FLIGHT 自动飞行3(91)
