(b)
MANUAL crossover altitude law (MAN XALT)
(Ref. Fig. 007)
MAN XALT is defined as a function of Mach (M):
-M less than or equal to 0.8:
MAN XALT = FL305
Hold Speed Display (in Line 2)
Figure 006
Manual Crossover Altitude Law
Figure 007
-M more than 0.8 and less than or equal to MMO: MAN XALT = FL305 + (MOXALT - FL305) (M - 0.8) / (MMO - 0.8) where MOXALT is the crossover altitude of (VMO, MMO) and FL305 is the crossover altitude of (300, 0.8).
1_ In the case of speed mode preselection (Ref. para. (a) above),
the speed value which has to be displayed in the FCU window
and used for guidance is initially the entered CAS for CLIMB
phase, the entered CAS or Mach for CRUISE phase.
2 To select directly a manual speed (CAS or Mach), the only way
_ is the FCU speed window, where the entered value is considered available only when speed manual is engaged and the value has remained constant for 2 seconds. Nevertheless, the FCU speed value is displayed also on the PERF page of active phase. If SPEED AUTO CONTROL is active, no manual speed is defined.
3 Following rules apply for display and guidance:
_ a A/C in CLIMB phase
_ FCU CAS entry
-
If the crossover altitude corresponding to the CAS is above A/C ALT and below CRZ FL at T/C, the system computes and displays the corresponding Mach value on the MCDU.
-
If it is not, no Mach is defined. FCU Mach entry
-No CAS is computed.
b A/C in DESCENT phase
_ FCU Mach entry
-
If the crossover altitude corresponding to the Mach is below A/C ALT, the system computes and displays the corresponding CAS value on the MCDU.
-
If it is not, no CAS is computed. FCU CAS entry
-No Mach is computed.
4 A special rule applies for descending in CLIMB phase or
_ climbing in DESCENT phase:
a A/C in CLIMB phase if:
_ -a Mach is selected on FCU (and no CAS is defined).
-
A/C ALT is at or above the crossover altitude corresponding to the Mach value.
-
A/C V/S is negative.
-CLR altitude is below crossover altitude, the system computes and displays the corresponding CAS on the MCDU.
b A/C in DESCENT phase if:
_ -a CAS is selected on FCU (and no Mach is defined).
-
A/C ALT is at or below the crossover altitude corresponding to the CAS value.
-
A/C V/S is positive.
-FCU altitude is above crossover altitude, the system computes and displays the corresponding Mach on the MCDU.
5 Following rules deal with automatic reference switch on FCU
_
during CLIMB or DESCENT phases.
a CAS ----> MACH if:
_
-a CAS is selected on FCU.
-the corresponding Mach is defined on MCDU.
-
A/C V/S positive.
-
A/C ALT is equal to the corresponding crossover altitude. The FCU display and the guidance speed become the defined Mach.
b MACH ----> CAS if:
_
-a Mach is selected on FCU.
-the corresponding CAS is defined.
-
A/C V/S negative.
-
A/C ALT is equal to the corresponding crossover altitude. The FCU window display and the guidance speed become the defined CAS.
(c) Speed envelope (used for predictions) Manual speeds are limited in the computation of predictions by the following speed envelope defined:
-
for the Minimum speed as VLS
-
for the Maximum speed as the smallest speed of: . VMAX . VMO/MMO . VMX CLB = maximum speed which can be held with Max Climb thrust in level flight.
NOTE : In case of engine out, VMX CLB is replaced by VMCT
____ (maximum speed which can be held with MAX continuous thrust on one engine and the other windmilling with anti ice on or off with respect to current conditions).
C. Vertical F-PLN Management
(1) Overview The vertical F-PLN management provided by the FMS mainly consists of two tasks which are computations of predictions and vertical guidance.
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