A320 alt fuel

[Flyman35]

During FMGC initialization usually we get to INIT NEXT PAGE to inter the block fuel and other info, sometimes I see the Alt fuel is lower than the flight plan Alt fuel (the reason as FCOM 4 states is that the calculation to alternate is based on cost index 0 ),now should I put the alternate fuel stated in the flight plan (which is higher by 200-300kg) or just leave the calculated as is, and appreciate if there is a reference, of course the Minimum Fuel on Board at Destination will be affected.

[flyer146]

Hello,

It is mainly due because you probably didn't enter any routing to your altn + approach in the primary F-PLN. So the distance taken by FMGC is direct dest to altn.
On the other hand, it is quite probable that your company provides you with a flightplan which plans the altn in a certain way (direct appr or full ifr appr, routing to altn longest or...).
Best is to check with your flightplanning department.
CI=0 means max range which is logic for an altn fuel calculation. I suppose your flt plan altn fuel is also max range (but check...).
Of course for not too far altns CI will not make that much of a difference...

I would use personnaly (see your sop's...) the FMGC to xcheck your company fltplan.
So I would force the required planning fuel to your altn in FMGC = flt plan
This will allow you to xcheck that you have enough for dispatching the aircraft (xtra fuel/time) ! (wind in there/step alts etc...to be 100% correct or at least be on the safe side)

In flight you can eventually remove this forced planning altn fuel after having entered the full route to your altn+full approach. Then you'll get the real fuel consumption along your routing and a new min diverting fuel.

FMGC doesn't take abnormal flaps/slats/gear... affecting your FF into account, be aware.

Be aware that the route you enter will maybe not be the one you'll receive, possible holding at your altn, which approach etc etc..... The idea is to land with final reserve at least at your altn this by operating the aircraft with anticipation.

Enjoy.

[Speed Freak]

are the weights for which the flight plan is made same as the actual weight on the particular date. lot of companies use seasonal flight plans with the take off weight based on the max t/o wt for that sector whereas you may be much lighter on that day, hence the difference in fmgc fuel calculation and paper flight plan calculation.

[I-2021]

By inserting the correct altn fuel you will get the same data you have in your FPL, which means having the paper lined up with the electronic data, which is good. Up to you really, the point is to get on the ground with the legal fuel.

[ThrustIDLE]

Hi there,

I've always been inserting hte ALTN RTE in the F-PLN page, with an SID, a route and the arrival as per our company OFP... I've normally got a value within a 100Kg... the difference arises when we update the INIT B page, with the actual weights from the loadsheet. As they are normally less than the planned one, the alternate fuel becomes a bit less due to the weight reduction.

As our colleague said before... the ALTN flight plan is normally computed at Cost Index 0 to allow Max Range. At least, this is what I know from our LIDO system.

[bond2002]

Also the FMC defolted level and the CFP alternate level is diffrent.

[toby320]

Hi, there are many things you have to take into account about your alternate fuel and many are describe in posts before mine but in my experience I rather not change any thing on the fuel predicted page, just is very important to feed the FMGC with all info related to your alternate and is very difficult to make the FP and FMGC match because the FP is made with specific weight,rute with specific sid and star,runway,flight level, and winds so all these conditions change from the time the dispatcher do your FP and the time of your flight so... As well is important to know that the fuel in your paper flight plan is the legal so you need to land follow these fuel.

My two cents

Toby. :ok:

[Dries]

So, to recap

FMGS' ALTN predictions are based on:
- CI 0
- cruise at FL220 if dist. to altn less than 200nm; FL310 if more
- no wind unless an altn wind was inserted in the DES WIND page
- direct routing unless modified by pilot.

All of the above have an impact on the displayed altn fuel required. The more parameters you modify iaw. the flight plan, the more the fuel prediction will match you FP's. If there still is a discrepancy after that, take the safe option ie. the highest fuel figure and you can't go wrong.