View Full Version : 744 FMS - Diversion fuel prediction techniques

14th Jan 2010, 12:19
Is their a way on the 744 FMS of predicting the fuel for a diversion route?

If I put a diversion in Route2 say from planned destination to an alternate, using SID's and STAR's, and then temporarliy make Route2 active, it assume I will be going from my present position to the destination for fuel predictions.

I would like an accurate figure from Destination (or point X) to Alternate using what I entered in Route 2.

I remember the Airbus FMS was much better at this...

Anyone got any tips?


14th Jan 2010, 12:59
I normally just use the info off of the flight plan.

But some of this might work..........

VNAV page landing fuel prediction will only look at fuel burn up to end-of -descent, so you can enter the route to the alternate after the missed approach for your landing airport in the active route. But that will not give you the landing fuel at the alternate that you are asking for.

So I would try and show a step descent on the legs page to around 1000' above the destination airport (put in well prior to, like 130 nm before the airport/airport navaid), so it would start you down at an appropriate point, then a step climb back up to your planned altitude and route to the alternate, and show the alternate as the actual landing airport. May also have to change the alternate to the destination airport on the route page. But not the neatest solution.

14th Jan 2010, 23:38
bigduke6 - Yeah, thats not a bad idea ... In fact could do on RTE2 and then activate in the cruize to see what its predicting at the new destination/alternate.

I was in this scenario a few days ago - Our planned ALT and destination were potentially snow closed so was scratching around for fuel and other alternates.

Re. The PROG page predictions - If you change the destination on there (not in RTE PG1) does that fuel prediction work if your not pointing at the newly entered airfield? I accept its a bee line straight line route .... but an indication from PPOS.

15th Jan 2010, 23:06
Don`t you have a `howgozit` ?!!

15th Jan 2010, 23:36
Don`t you have a `howgozit` ?!!

Whats thats?

Were lucky to get an abacus!

15th Jan 2010, 23:44
You need all available means to make a solid decision.

LIDO FLTPLNs are calculateted for 4 ALT and with a very favourable RTE. Sometimes allmost DCT. These all 4 might just have become obsolete and you need a new set of Airports. So how do you get a more realistic mileage and fuelprediction? Use your FMS!

If you change the DEST on ACT RTE then there will be an automated message generated to your Dispatch. We had a Tropical Cyclone over Manila and used this tool to try a couple options... After a while we got an ACARS from FRA where the heck are we going to land.;-)

The Fuelpredictions on the B744 are pretty unaccurate towards the end. You can almost every time subtract a 1000kgs from the predicted fuel on arrival. Especially if there is a big difference between calculated and totalizer. So make a correction for that.

RTE2 is a good option, just dont execute it. Try to put next waypoint on LSK 1L and a new DEST. Optimize the CRZ alt with /F150S for example. The problem lies in the details.What Wind will you have? Its pretty tought to figure out what FL you get, and that makes a big difference. So i would go with mileage, divide with a conservative TAS and get flighttime. Multiply with average FF and get Tripfuel. This would be Overhead to Overhead Planning. Pack your personal Extrafuel on top and thats pretty much is it.

The FMS predictions have one great disadvantage. GIGO. In lack of valid input the predictions are useless. They just pretend to be accurate to .1 tonn.



16th Jan 2010, 10:59
Do you have the Nearest Airport/Alternate Airport page on you FMS?

With this page available:

Add your route for diversion to alternate on the active plan page, after the end of the missed approach. You will need to use the four letter ICAO code for the airport as the last item, as you won't be able to add STAR or approach for the alternate airport.

Now go to the Alternate Airport page, and enter and select your Alternate airport. Now select the fuel at alternate "Via Missed Approach".
The FMS will calculate your descent and approach to your destination, then use the missed approach route you have entered (which now includes the flight rout to the alternate), then a straight track to the alternate airport (zero distance, in this case).

Take off your normal approach and landing allowance from the figure you receive.

NB - I fly the 737, so this may or may not work for you. ;)

16th Jan 2010, 17:39
Checkboard - We dont have an ALT page on the 744, which we did! Sounds a bit like the FMS on the Airbus which I miss for the diversion planning.

warmkiter - You must fly to FAA ops with a dispatcher 'in control'.
Here in the UK/EU no ones watching the destination change!
Some good hints there ... Its a shame RTE2 needs to be activated to get fuel predictions, but then it assumes from PPOS.

I have used RTE2 to work out an accurate mileage and pro-rata one of our flight plan div's fuel/mileage ... I think thats probably the easiest solution, although as you say worth adding a wind/alttitude saftey factor.

16th Jan 2010, 22:06

its firmly JAA ops and everybody controls his on turf. that is how the big system works. you would be amazed how much data your aircraft is sending down during a flight. Just check for example the AF447 accident. Every airline has got an OPS control. Drop by and ask the guys what automated reports they get downlinked via ACARS. I bet change of destination will be one trigger...

As previously mentioned, i would not trust too much the FMS predictions, because of so many unknown variables.