Good afternoon gentlemen (and ladies),
First time posting on this forum. I cant believe I stumbled onto this forum by chance. Incredible wealth of knowledge here! :ok:
Anyway, I write programs & speadsheets for Aviation & Electronics stuff. I have a question about the term "Fuel Reserve" & Fuel on Board. I'm working on a block of code for fuel data/endurance information.
For instance;
Fuel Reserve / Fuel Flow = Endurance in Hours
Does Fuel Reserve and/or Fuel on Board mean only "usable fuel"? Or, does it include the "unusable fuel" in the fuel system?
If an airplane has 50-Gal fuel capacity, of which 48-Gal is "usable", do I use 48-Gal as my Fuel Reserve/Fuel on Board value?
Just want to be sure I'm using the term correctly.
Thanks
Monty Cristo
14th Feb 2009, 19:59
If the fuel can not be used, there is no point in including it in endurance calculations. You can only burn fuel that can be used. The unuseable fuel sits in the system pipes and is not accessible to the engines fuel pumps.
eckhard
14th Feb 2009, 20:19
Hi n9xv
This is a reply I sent to a previous post about fuel planning. It may be useful to you; if not, I apologise.
Here are some notes which you might find useful. They are 'JAR-OPS generic' but I may have used some 'company-specific' terminology here and there:
FUEL PLANNING NOTES
TIF TRIP FUEL Fuel for take-off, climb, cruise, descent and approach at destination using forecast winds and planned Flight Levels on the route filed with ATC.
CONT CONTINGENCY 5% of TRIP FUEL to allow for unforecast winds, lower than optimum levels, ATC re-routes, etc.
DIV DIVERSION Fuel for go-around, missed approach, climb, cruise, descent and approach from destination to the alternate airport using forecast winds, levels and routing as listed on the flight log.
RES RESERVE Final Reserve sufficient for 30 minutes holding at 1500ft above the alternate airport.
REQ REQUIRED Fuel Required at the start of the take-off roll. It is the sum of TRIP, CONT, DIV and RES fuel. (Actually it is permissible to use CONT fuel before take-off, but unwise to use it all.)
DECMP DECOMPRESSION Not generally required for European operations. It is only relevant for long-distance flights over water (e.g. ETOPS). Sometimes referred to as ADDITIONAL Fuel
EXTRA EXTRA Extra fuel at the discretion of the captain to allow for holding at destination, anti-icing, etc. Can also include 'Tankering' Fuel.
TAXI TAXI Sufficient fuel allow for APU use, engine start and taxi before takeoff.
TANKS The Total of all the above. The fuel in the tanks before engine start.
Some other definitions:
FINAL RESERVE is enough for 30 minutes holding at the alternate airport (after diversion). If you dispense with an alternate (i.e. you 'commit' to landing at your destination), this is the minimum fuel that you must land with. If it is likely that the aircraft will land with less than this amount, you should declare a 'Mayday'.
TOTAL RESERVE is enough for a diversion to the alternate airport followed by 30 minutes holding. It is the sum of DIV and RES fuel. Sometimes called COMPANY MINIMUM RESERVES (CMR). Some companies have a 'minimum' CMR, e.g. 2000kg for a 737. I think this is the figure referred to in some posts.
PLANNED REMAINING is what you expect to land at the destination with. It is the sum of CONT, DIV, RES, DECMP and EXTRA fuel.
So you see there is no requirement to allow for 'holding' at destination. A sensible crew will take EXTRA fuel to cater for holding at destination, if they feel it is justified. On a 'normal' flight, they will arrive with PLANNED REMAINING, and so have some holding capability at destination in any case.
Hope this helps to clear up what can be a complicated subject (not helped by different terminology being used by different operators).
I see your point Monty Cristo, if you cant use it - it does'nt count. :eek::)
Thanks also Eckhard,
That's a great breakdown of the terminology involved. I'll copy paste that in my archives for reference. I'ts really cool to key in a handfull of values in the spreadsheet and watch it "explode" with information.