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DES Mode: Aircraft above Profile -Hold of Upper Speed Margin in SPEED AUTO CONTROL
Figure 023
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DES Mode: Aircraft below Profile in SPEED AUTO CONTRL
Figure 024
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APPROACH Pages (APPR)
Figure 025
FINAL Mode (A/C on Approach Profile)
Figure 026
Theoretical Approach Profile
Figure 027
Theoretical Approach Profile with an
Intermediate Altitude Constraint
Figure 028
The system can engage the FINAL mode only in APPROACH phase, when the aircraft is close enough to the lateral and vertical approach paths and beyond the DECEL point. FINAL cannot be engaged unless a vertical approach path is defined. It is disengaged below MDA minus 50 feet or if the vertical path is modified or if the last approach waypoint (runway or MAP) is sequenced, and the autopilot is disconnected. When the FINAL mode is engaged, VPATH-SPEED submode is selected: elevators are used to control the aircraft to the path and speed is held with thrust. Pitch authority is limited with regards to aircraft vertical acceleration and vertical speed. FCU selected altitude is ignored. When the FINAL mode is armed or engaged, the vertical flight path altitude at computed aircraft position is displayed relative to aircraft altitude on a specific plus or minus 200 ft precision V/DEV scale on the PFD.
c_ SPEED AUTO CONTROL
Throughout approach phase, the FM transmits to the FG a
display speed target equal to VAPP, and a guidance speed
target equal to VAPP lower limited to FAC maneuvering speed
(VFTO, S, or F), except when the selected landing
configuration is extended: VAPP.
The FG uses the FM display and guidance speed targets which
can be modified as a function of measured headwind and the
headwing component of the destination wind entered on the
PERF APPROACH page (Ref. 22-13).
(g) GO AROUND phase
1 Parameters
_ Flap retraction, Slat retraction, and VFTO displayed on the PERF GO AROUND page are computed with predicted landing weight and CG. At transition to GO AROUND, they are computed with current values and frozen. Thrust reduction and acceleration altitude are also defined in a similar way as for TAKEOFF.
2 Predictions
_ Only destination predictions are provided. They assume level flight at FCU selected altitude with a CAS of VFTO and no wind.
3_ Guidance
- Transition to GO AROUND occurs upon SRS mode engagement.
- At thrust reduction altitude, the CLB indication flashes
until the throttle control levers are set to CLB.
- At acceleration altitude, OPEN CLB mode is engaged if the
aircraft is below FCU selected altitude.
- In SPEED AUTO CONTROL, when SRS mode is disengaged, the
speed target is VFTO, upper limited to speed constraints if
NAV mode is engaged.
- CLB or DES modes are not available in GO AROUND phase.
(3) SPEED MANUAL CONTROL-Specific Rules (Ref. Fig. 029) The task of the FMS concerning manual speed selection, preselection and CAS/Mach switching at manual crossover altitude is described in para. 2.B. The following paragraphs give the effect of selection of speed manual mode on predictions and vertical guidance.
(a)
Effect on predictions In the computation of predictions, the ECON speed is replaced by the FCU selected speed for the actice phase and by a preselected manual speed for a future phase. In a more specific way, predictions assume that the selected speed will be maintained until the end of the phase in cruise or until the next point where the ECON speed becomes greater than the FCU selected speed or MCDU preset speed in CLIMB, or smaller than the FCU selected speed in DESCENT. ECON speed is assumed thereafter. (Ref. Fig. 030) Furthermore, in descent, no speed margins are defined and return to pathfrom above is predicted based on hold of selected FCU speed, idle thrust and speedbrakes extended to mid travel.
(b)
Effect on guidance
-In speed manual control, the speed selected on the FCU is necessarily the target either on elevator or on thrust with respect to the submode engaged. Besides, the choice of mode, submode and the computation of the second target is as described for speed auto control. One exception is in Descent because no Speed margin may be defined ; the following logic applies when DESCENT mode is active. Guidance initially holds precomputed profile on elevator and FCU selected speed on thrust.
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