(3) Fuel planning 
R  Two fuel functions are provided within the FMGC. The first one 
R  consists in fuel planning which computes the necessary fuel to fly a 
R  specific flight plan. The second one is the fuel prediction function 
R  which gives the predicted fuel at landing, landing weight and 
R  expected extra fuel. 
R  (a) Fuel planning 
R  If a flight plan has been inserted as well as a CRZFL and a cost 
R  index, the crew has the possibility through the INIT B page to 
R  introduce the zero fuel weight and center of gravity for zero 
R  fuel weight. 
R  (Ref. Fig. 037) 
R  Therefore, the system, on request by the crew (by pushing the 
R  line key adjacent to the FUEL PLANNING indication), assuming 
R  extra fuel of zero, computes the minimum fuel to meet the 
R  requirements of the flight, taking into account a predetermined 
R  fuel policy (Ref. Para. (d)). 
R  BLOCK = TOW + TAXI - ZFW = TAXI + TRIP + RSV + ALTN + FINAL 
R  LW = TOW - TRIP 
R
 (b) Fuel predictions
 This function is performed automatically when the crew has
 inserted a flight plan (origin and destination) with CRZ FL and
 ZFW inserted.
 In addition, the system has to know the Fuel On Board inserted by
 the crew (BLOCK fuel) or computed by the system before engine
 start (at engine start, fuel predictions are automatically
 computed based on the FOB value as as available output from the
 Fuel Quantity Indicator (FQI).
 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:
 - in preflight phase before engine start:
 TOW = ZFW + BLOCK - TAXI
 EXTRA = BLOCK - TAXI - TRIP - ALTN - FINAL - RTE RSV
 LW = TOW - TRIP
 - in preflight phase after engine start:
 EXTRA = FOB - TAXI - TRIP - ALTN - FINAL - RTE RSV
 LW = GW - TRIP - TAXI
 - after transition to Takeoff phase:
 EXTRA = FOB - TRIP - ALTN - FINAL - RTE RSV (if in fuel policy)
 LW = GW - TRIP 

 (c) MCDU mechanization (Ref. 22-71-00) Fuel planning is performed through and displayed on the INIT B page. For a SECONDARY flight plan created via the SEC INIT page, the function is available through the SEC INIT B page. Fuel prediction is performed through and displayed: - on the INIT B page before engine start - on the FUEL PRED page after engine start - on the VERT REV page - on the F-PLN B page. (Ref. Fig. 037, 039)

 Fuel Predictions on F-PLN B and VERT REV Pages
 Figure 039

 (d) 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 planning and fuel predictions, a fuel policy is determined in the AMI file (Ref. following table). For these records in which data are not provided, default values, as given in third column, are given. Furthermore, the four following parameters can be modified on the MCDU through the INIT B and FUEL PRED pages: RTE RSV, FINAL TF, FINAL TG and TAXI.
 -------------------------------------------------------------------------------| MNEMONICS | PARAMETERS | DEFAULT |Resolutn | | | VALUES | |-----------|--------------------------------------------|-----------|---------| RTE RSV % | Percentage of route reserve | 5% | 0.1% |-----------|--------------------------------------------|-----------|---------| RSV MIN | Minimum value of route reverse | 0 kg |100kg |-----------|--------------------------------------------|-----------|---------
------------------------------------------------------------------------------| MNEMONICS | PARAMETERS | DEFAULT |Resolutn | | | VALUES | |-----------|--------------------------------------------|-----------|--------| RSV MAX | Maximum value of route reserve | 100,000 kg| 100kg |-----------|--------------------------------------------|-----------|--------| RSV IN FLT| Reserve remains computed in flight | yes | |-----------|--------------------------------------------|-----------|--------| RSV ALTN | Route reserve is computed with alternate | no | | | trip fuel | | |-----------|--------------------------------------------|-----------|--------| FINAL TF | Time in which the final holding pattern | 30 min | 5min | | is supposed to be flown. Used for fuel | | | | predictions | | |-----------|--------------------------------------------|-----------|--------| FINAL TG | Time in which the final holding pattern is | 30 min | 5min | | supposed to be flown.Used for fuel planning| | |-----------|--------------------------------------------|-----------|--------| FINAL FIX | Fuel burnt in the final holding pattern. | 0 kg | | | Used for fuel predictions | | 100kg |-----------|--------------------------------------------|-----------|--------| FINAL ALT | Altitude at which the final holding | 1 500 ft | | | pattern is supposed to be flown | | |-----------|--------------------------------------------|-----------|--------| TAXI | Fuel for taxi | 200 kg | 100kg |-----------|--------------------------------------------|-----------|--------| FINAL DEST| Final holding pattern is flown at primary | Alternate |  ------------------------------------------------------------------------------| MNEMONICS | PARAMETERS | DEFAULT |Resolutn | | | VALUES | |-----------|--------------------------------------------|-----------|--------| | or alternate destination | | ------------------------------------------------------------------------------
　
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