I did some testing on this topic for my fuel planner software.

I came to the conclusion that if EXTRA TIME on thr WEIGHT INIT Page is smaller than 0 (no extra time) this message is triggered. EXTRA TIME is that amount of flight time available after you burnt all your reserves, if it is smaller than 0, it means that you don't even have enough fuel onboard to include the nessescary reserves (reseves entered on the same page).

 

Hope that helps,

 

Jonathan

Hi,I'm having fuel/CoG problems, could I ask what method you use to determine how much fuel is required for your flight?Regards,

 

I am using FSCalc for iOS on my iPhone, together with wind predictions from AS2012, I am spot on every flight.

I did some testing on this topic for my fuel planner software.

 

I came to the conclusion that if EXTRA TIME on thr WEIGHT INIT Page is smaller than 0 (no extra time) this message is triggered. EXTRA TIME is that amount of flight time available after you burnt all your reserves, if it is smaller than 0, it means that you don't even have enough fuel onboard to include the nessescary reserves (reseves entered on the same page).

 

 

Hope that helps,

 

 

Jonathan

 

Jonathan, so you put also EXTRA TIME? I only use RSV FUEL. Is it mandatory to insert an EXTRA TIME value?

Hello Riccardo,

 

 

Jonathan, so you put also EXTRA TIME? I only use RSV FUEL. Is it mandatory to insert an EXTRA TIME value?

No, you don't have to enter anything into EXTRA TIME.

If we look onto the weight int page we have 5 values on the lefthand site.

The first line shows the TRIP/TIME needed for our route, calculated by the FMC.

The second line shows RTE RSV/%, which is contengency fuel. We leave that on 10% (some airlines use other percentages, but 10% should do well.

The third line shows FINAL/TIME. This is the time for holdings, delays, etc. I either use 30 or 45 (expecting much traffic, bad weather) minutes, if I expect more delays of e.g.: 30 minutes I will add that to the 45 minutes => FINAL/TIME = 75 minutes.

The last field is EXTRA/TIME. It is also calculated by the FMC.

The formula for that is:

Fuel on board - Taxi Fuel - Route Fuel - RTE reserve Fuel - Final Fuel = Extra Fuel

If your Extra Fuel < 0 you will get the Insufficient Fuel meassage.

If your Extra Fuel > 0 you will be fine.

Thank you very much Jonathan for your explanation, very useful, but reading directly from 10.20 FMS manual:

 

"EXTRA/TIME - This fuel value is calculated by adding all required fuel (above) and subtracting that total from the BLOCK fuel. Should negative values be displayed, it indicates the flight may be into reserve or holding fuel. An INSUFFICIENT FUEL message will be displayed in the SP if extra fuel is zero or less."

 

So the EXTRA TIME=UFOB- (taxi+trip+rte+alt+final) is correct?

 

Just now I can't verify planned fuel for my last route. In half an hour I can do that.

 

So I'll be more precise.

You'r welcome!

 

So the EXTRA TIME=UFOB- (taxi+trip+rte+alt+final) is correct?

 

That should be it.

Here I am Jonathan, this is my last route EHFK-VIDP:

 

                  FUEL    CORR    ENDUR
TRIP              40124  ........  06:14
CONT 5%        2006  ........  00:22
ALTN VIAG      2944  ........  00:22
FINAL RSV      2682  ........  00:30
HOLD              2698  ........  00:30
MIN T/O        50454  ........  07:58     
EXTRA            1000  ........  00:11      
TAXI                  450  ........  00:10       
RELEASE     51904  ........  08:19

 

I find the error: the default value for contingency is 10%, but I've not updated it with planned /5% (as above). Leaving /10% I got and EXTRA TIME of -1.5 so the correct INSFUFFCIENT FUEL msg.

 

Do you confirm that FINAL RSV value (2.6) is to be inserted under FINAL/TIME field on FMC?

 

Thank you very much for your patience, now I'm really happy to have found the error Jonathan!

Do you confirm that FINAL RSV value (2.6) is to be inserted under FINAL/TIME field on FMC?

 

Yes, that's correct!

 

Best regards,

 

Jonathan

Hi Jonathan, I planned this trip: EHAM-SAEZ with 110.600 kgs of FUEL

 

After filled UFOB with this value my EXTRA TIME is <0 so I'll get INSUFFICIENT FUEL msg.

 

If I want UFOB>0 with EXTRA TIME positive I have to put 113.000 kgs, 2400kgs more.

 

I got 110.600 kgs from TOPCAT and similar from other flue planning tool, such as FSBuild.

 

So in your opinion why there is this discrepancy in fuel planning.