I know that the RESERVES fuel entry on the PERF INIT page is (normally) the sum of ALTN (if applicable) and FINAL RESV from the PFPX briefing. On long flights with a significant 5% contingency, this usually means landing with a fuel load a reasonable amount above the RESERVES entry, and not getting a INSUFFICIENT FUEL message.

 

However, each aircraft/operator also has a minimum fuel level (for example, 2,300kgs for Ryanair's 737s; I think it's 8,000kg for the 777 and 12,000kg for the 747 - might not be exact but you get the idea).

 

PFPX can accommodate this with a remaining fuel entry, but if you set this entry to the minimum fuel level as above, and in the FMC RESERVES, it doesn't leave any margin before getting an INSUFFICIENT FUEL message.

 

How is this normally dealt with real world?

I was doing this incorrectly by just using the Final RESV without adding the ALTN.  Thanks for the info, sorry I cannot answer your question.

Good question. Have you also tried asking at the PFPX forum?

From the "BIG BOEING FMC USERS GUIDE" by Bill Bulfer (page 78, to be specific)

 

"1) The purpose of the entry in the RESERVES field is to initiate the FMC message, INSUFFICIENT FUEL.

2) While you must dispatch and takeoff with at least the reserve fuel stipulated by regulation (FAR121.639 and FAR121.645), there is no regulatory requirement to land with that amount.

 

Some operators publish guidelines for the minimum fuel on board for landing. These values fall in the range of 15 to 30 minutes of maneuvering fuel. One operator refers to this as Minimum Desired Landing Fuel (MDLF). Some pilots have personal minimums in excess of these numbers. The point on which we may agree is that the Captain is responsible for determining the minimum fuel that he or she must have on board at the destination or the alternate.

 

Boeing and most operators specify that "FAR Reserve" Fuel be entered in the PERF INIT page. While the warning message INSUFFICIENT FUEL, would be valid at break release on takeoff (the point at which the flight "officially" begins) it might nnot provide a meaningful warning after the airplane had detoured through a thunderstorm or two.

 

Additionally, there can be significant differences between FAR fuel on a domestic flgiht and on an international flight. In equivalent terms, the '...45 minutes at normal cruising fuel consumption' (calculated by one operator at FL250) can be as little as 30 minutes sing the same criteria and the provisions for a close-in Redispatch. One operator's procedure solves the inconsistency dilemma between domestic and international reserves: Minimum RESERVE fuel entries: The Captain may choose a larger value than those listed here, but should avoid values which result in spurious INSUFFICIENT FUEL messages:

 

1) If no alternate is required, enter Minimum Desired Landing Fuel or FAR fuel whichever is greater.

2) If an alternate is required, enter burn to most distant alternate, plus MDLF.

3) If no alternate is named, but Minimum Arrival Fuel is required (such as Sydney or Hong Kong), enter that value

4) If alternate is deleted or added enroute, update the reserves fuel line.

 

End Quotation"

 

So what does this mean practically? A couple of things:

 

1) There is no "set" amount that is to be entered...it is not something that is on the flight plan per se, since there are variations as to what could be entered

2) The Captain is the one who makes this decision and updates the reserves line in the PERF INIT page as changes are required en route (e.g. add or delete an alternate).

 

From a dispatch standpoint, we operate with FAR fuel, which we otherwise call MIN FUEL. You will see a min fuel line (MIN T/O) on the PFPX flight plan. MIN FUEL is defined as trip fuel, reserve fuel, hold fuel and alternate fuel. EXTRA fuel is simply fuel that is added by the dispatcher or captain as additional fuel which is onboard but not required fuel. For domestic and international operations, this is the minimum fuel that must be on the aircraft at takeoff. One pould (or kg) less and you go back to the gate and get more fuel.

 

A simple way of thinking about reserve fuel is "what fuel MUST I have when I land?" A diversion decision is a great place to think about this. There is always a point in a flight by which you must make a decision to divert if you can't get into the airport to which you are flying. I do diversion calculations almost daily and the fuel required to get to the alternate plus the reserve fuel are the absolute minimum required fuel at the time of the diversion decision.

 

For the captain, this is BINGO fuel and if you think in terms of...."When I hit this number, I must divert or be on the ground at my destination".

 

SO...my recommendation would be to do this math:

 

FAR RSV (or whatever reserve is dictated if you use EU Rules or JAR OPS) plus ALTN fuel (if an alternate is specified). The total of those two figures from your flight plan is your "RESERVES" that you enter on the PERF INIT page of the FMS.

 

Put another way:

 

An example.... Boeing 737-800 Winglets

Fuel numbers as follows: KLAX-KSFO ALTN KSMF

 

TRIP                  5446  /  00:55

ALTN KSMF       2230 /   00:22

FAR RSV           3775  /   00:45

MIN FUEL         11584  /  02:02

EXTRA               2406  /  00:30

TAXI                     750  /  00:30

RELEASE:       14600  /  03:02

 

The amount you would put into the PERF INIT page in the FMC:

 

BLOCK FUEL: 14.6

RESERVES:      6.0 (6001) ALTN + FAR RESV.

 

If you use the concept of BINGO fuel as the basis of your RESERVES entry in the FMC, you should never get an INSUFFICIENT FUEL message until your onboard fuel hits 6.0....

 

..and you will always know when you need to be on the ground OR if you have an alternate included, by when (in lbs/kgs) you must divert.

 

In closing, I know I've put a lot of information here, but there is an important concept here, not just an entry issue....you ALWAYS want to know your BINGO fuel number, since if you get to this point, you better be on the ground or diverting somewhere. 

 

Hope this explanation is slightly clearer than mud.

 

Cheers,

Dave

You, Mr. Lamb, sir, are a gentleman and a scholar!

Great insight!

Cheers..

Dave, thank you, awesome insight!

 

Cheers,

Thanks Dave!

That's very helpful, David. Thank you.    ^_^

 

Cheers,

 

Brian

Thanks for this clear explanation David, I was always curious about what components make up the Reserve figure in our FMCs.   All my questions have been answered!

Thanks for the insight Dave!

Your explanations were fantastic and they helped me a lot!

 

By the way, I must add... I thought that you would get the 'Using Resv Fuel' message instead of the 'insufficient fuel' message when you hit the RESV Fuel level.

'Insufficient Fuel' message would only pop up if your planned or current fuel is lower than the fmc calculated en-route fuel to destination, or so I've heard...

 

Cheers, Murphy

So just to clarify in PFPX offplan:

 

RESERVES = FINAL RESV + ALTN ?

 

Look at this OFP:

 

http://www.flightsimsoft.com/pfpx/pics/7.jpg

 

The sum is 6045, so on INIT page I have to put 6.0, correct?

 

This is alid for every aircraft I suppose.

Thanks for the insight Dave!

Your explanations were fantastic and they helped me a lot!

 

By the way, I must add... I thought that you would get the 'Using Resv Fuel' message instead of the 'insufficient fuel' message when you hit the RESV Fuel level.

'Insufficient Fuel' message would only pop up if your planned or current fuel is lower than the fmc calculated en-route fuel to destination, or so I've heard...

 

Cheers, Murphy

 

I can't find any reference in the FCOM to 'USING RESV FUEL' nor can I get the message to appear by dropping my fuel level below the RESERVE fuel level.

I can't find any reference in the FCOM to 'USING RESV FUEL' nor can I get the message to appear by dropping my fuel level below the RESERVE fuel level.

The B777 will message Unsufficient fuel when the estimated fuel will get into reserves.

 

The sum is 6045, so on INIT page I have to put 6.0, correct?

Seems to be alright although I round these figures always up. So in my case 6.1

I am using a PFPX OFP flightplan for a long haul between KMSP and RJAA, and on my fuel sheet I don't have a reserve field.

I am using the U.S. Flag (Jet) fuel policy and see the following figures in my plan:

 

 

 

Do I add Intl Hold to my Altn to get my FMC Reserve?

 

EDIT: nevermind, I found that the Delta OFP template I use actually has an FMS reserve field!

It was 13067, which means I answered my own question!

The B777 will message Unsufficient fuel when the estimated fuel will get into reserves.

Read my post again.