(g)
APPROACH phase Same as DESCENT, both DES and FINAL modes are available.
(h)
GO AROUND phase All predictions are dashed. The speed target is the same as when both engines are running.
(3) Fuel Predictions This function gives the predicted fuel at landing, landing weight and expected extra fuel. It is performed automatically when the crew has inserted a flight plan (origin and destination) with CRZ FL and CI defined and ZFW inserted. In addition, the system has to know the Fuel on board inserted by the crew (BLOCK fuel) before engine start or communicated by the fuel quantity sensor to the FMGC at engine start. Once these items of information are available, the FMGC computes the flight plan predictions including time and fuel at all waypoints. Landing weight, alternate fuel and extra fuel are also computed, taking into account the predetermined fuel policy:
-Before engine start.
EXTRA = BLOCK - TAXI - TRIP - RSV - ALTN - FINAL
TOW = ZFW + BLOCK - TAXI
LW = TOW - TRIP
-After engine start. EXTRA = FOB - TAXI (in Preflight) - TRIP - RSV - ALTN - FINAL LW = GW - TAXI (in Preflight) - TRIP
Note that FINAL FUEL is not substracted from EFOB at primary or alternate destination.
(a)
MCDU mechanisation
Fuel prediction is performed through and displayed on:
-
the INIT B page before engine start
-
the FUEL PRED page after engine start
-
the VERT REV page
-
the F-PLN B page.
The VERT REV page at waypoint X displays the predicted EFOB at X
and the predicted EXTRA at X.
EXTRA (X) = EXTRA (X-1) + RSV (X - 1, X)
Where RSV (X - 1, X) is the value of the reserve for the portion
of trip between X - 1 and X.
F-PLN B page repeats the predicted EFOB at X.
(Ref. Fig. 038, 040)
(b)
Fuel policy Due to the various airline fuel policies and to the fact that the system needs to know on which parameters it has to perform Fuel predictions, a fuel policy is predetermined (Ref. following table). Up to eight fuel policy records may be specified in a specific nav Data Base and selected by pin programming. For these records in which data are not provided, default values, as given in third column, are given.
Fuel Predictions on F-PLN B and VERT REV pages
Figure 040
Furthermore, the four following parameters may be modified on the
MCDU through INIT B and FUEL PRED pages : RTE RSV, FINAL TF,
FINAL TG and TAXI.
A special rule applies for final fuel/time: final time is used
for fuel prediction only if final fuel is not defined.
-------------------------------------------------------------------------------| MNEMONICS | PARAMETERS | DEFAULT | | | | VALUES | |---------------|---------------------------------------------|---------------| | RTE RSV | Percentage of route reserve | 5 % | |---------------|---------------------------------------------|---------------| | RSV MIN | Minimum value of route reserve | 0 kg | |---------------|---------------------------------------------|---------------| | RSV MAX | Maximum value of route reserve | 10,000 kg | |---------------|---------------------------------------------|---------------| | RSV FL | Reserve is computed for fuel predictions | yes | | | in flight | | |---------------|---------------------------------------------|---------------| | RSV ALTN | Reserve includes reserve of alternate | no | | | trip | | |---------------|---------------------------------------------|---------------| | FINAL TF | Final time used for fuel predictions | 30 min | |---------------|---------------------------------------------|---------------| | FINAL FIXF | Inclusive final fuel used for fuel | 0 kg | | | prediction computation | | |---------------|---------------------------------------------|---------------| | FINAL ALT | Altitude of the holding pattern which | 1 500 ft | | | the final computation is based on | | |---------------|---------------------------------------------|---------------| | TAXI | Taxi fuel | 200 kg | |---------------|---------------------------------------------|---------------| | FINAL DEST | Airport upon which the final fuel | Alternate | | | computation is performed | | -------------------------------------------------------------------------------
FUEL POLICY
(4)
Altitude Planning When the A/C is in takeoff, climb or descent flight phase, the FMGC computes the time (UTC) when the A/C reaches a specified altitude (FCU altitude is the default value) and the corresponding distance. (Ref. Fig. 039) Two performance modes exist:
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