Correct B777 fuel loads?

[40&80]

Rumour is....Some B777 operators fuel loads allow for unuseable fuel on an individual aircraft basis and this unuseable fuel figure is programmed into their fuel planning computer.
Rumour also is....Other B777 operators fuel planning computers are not programmed to allow for unusable fuel.
Is there in fact unusable fuel shown in the B777 limitations section of the flight manual?
If so can both methods of fuel calculation be shown to be legally correct?
Are B777 Captians aware of the way their company fuel computer is programmed as regards useable and unuseable fuel?

[Rainboe]

Nobody can really say what an 'unuseable' fuel load is. For a start, nobody is going to test it inflight, and it will vary with attitude and bank (yes I know a balanced turn will theoretically not affect it, but it does). The manufacturer can only give a rough estimate which is presumably incorporated into individual performance calculations. I am not aware of such a figure on the last 3 Boeings I have flown, so I doubt whether the crew are informed of any figures on the 777. T!he whole point of aviating is not to test the figure! It really does not concern the pilots, anymore than people don't worry about running out of gas in their cars between stations. It you'r that tight, you should be getting it on the ground, not looking at fuel gauges

[40&80]

Well Rainbow... I guess you never flew the the B767 I flew...
Boeing actually states there 2000kgs of fuel as not available in the limitations section of the flight manaul.
When I find out what it is on the B777 I will let you know.

[Rainboe]

The only current Boeing I didn't fly! It's a figure not banded about on the others, as far as I know, or nobody is telling me! But when you have more than one wing tank/wing, quoting a figure is not really practical. And no figure is quoted for the 737.

[BOAC]

Unusable fuel is by definition fuel that cannot be used in flight with wings level and at cruise angle of attack(or nose 3° up). Nothing to do with 'bank'!.

I believe the 737 is calibrated to read zero with UF remaining.

Previous discussion.

'Traditionally' UF is included in the 'Dry' Operating Mass. I'm a bit confused by your (now edited) post as to why anyone would include UF in fuel figures?

[Old Smokey]

A B777 Specific answer :-

(1) All Fuel figures quoted in the AFM and other Operating Manuals, either Volume or Mass, are for USABLE fuel.

(2) The Fuel Gauges, and FMC Fuel calculations are for USABLE fuel.

(3) The UNUSABLE fuel is not information available to pilots (useless information), the Engineering Manuals DO have that data.

(4) Flight Planning is based upon USABLE fuel ONLY.

(5) The UNUSABLE Fuel Mass is included in the Basic Operating Weight (BOW).

Regards,

Old Smokey

[40&80]

Thank you Smokey for clearing that up....My concern as a B767 pilot "was" because the Boeing manual I was issued with as a pilot listed 2000ks as unuseable and I was required to know and spout this figure on my 6 monthly base/sim checks...and I honestly always thought this was relevent information for me as a pilot.
Retired I asked the question regarding the B777 unuseable fuel on behalf of some other pilots who are relutent to ask their managers.
If all the various airlines flight planning computers are correctly programmed then there is no problem...however I often worry who guards the guards these days...and who actually double or triple checks the correct weights and programmes.
I was quite spooked on running out of fuel when a Pan Amm B747 diverted years ago and the engines stopped on landing roll...the fuel diversion fuel diversion fuel tables were found in error....I also got a twitch when I read the NZ DC10 waypoints were changed by one man working alone before dawn and it hit a mountain in the antartic.
The longer I live the more inclined I am to double check the information given to me initially by experts and to get a second opinion...I also observe that agencies set up to supervise and control various functions
often fall short of doing a proper job.
Again many thanks for posting.

[BOAC]

Originally Posted by 40&amp

I was issued with as a pilot listed 2000ks as unuseable and I was required to know and spout this figure on my 6 monthly base/sim checks..

- as we have discussed elswhere, I am interested to know what you were expected by the glitterati in that company to actually DO with this 2000kg 'knowledge'. I have to guess at a 30 min reserve for a 767 - I'll stab at 2600kg. Did your Final Reserve include UF - ie was it 4600kg, or did you just use 2600kg? After all, all a pilot wants to know when he looks at the fuel guages is 'what have I got to fly with?' Did you add the 2000 to DOM every time? It smacks to me of an arcane piece of 'fact' that someone in your company had got hold of and wanted everyone to know he knows - know what I mean?

[One Outsider]

I seriously doubt that there are 2000 kgs of unusable fuel on a 767. It would be a poorly designed tank and fuel system for that to be the case. I suspect that for an aircraft of that size the unuseable fuel is in the order of 200-300 kilos. In any case, I am unaware of any aircraft where the FQI is calibrated to include unusable fuel.

2000 kilos of unuseable fuel sounds more like what is the case when gravity feeding.

[Bob C]

I know of two situations regarding fuel on an aircraft that is not indicated in the cockpit. One is called trapped unusable fuel which is include in the dry weight of the aircraft provided by the manufacturer, the other is trapped usable fuel which is significant. On a B747-400 it can be as much as 1000 lbs. This is the fuel that is in the fuel lines and manifold that are part of the delivery system to the engines and therefore is not measured by fuel quantity probe which are in the fuel tanks.
Regards