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Beardyman

Fuel planning question

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Question about real world procedure regarding fuel reserves for 747.

In the PMDG Manual it is stated that 747 needs to keep min. 13608kg of fuel only for the purpose of cooling hyd. pumps.

If so then i understand that during landing 747 needs 13.6k kg + reserves coming from normal route planning like holding, alternate airport etc... 

 

As can see YT movie (

) LH 747 made her flight with fuel reserve less than 10T

I believe that guys at Lufthansa know how to plan fuel and less than 10T is not a planning error, but how does it fit to above given fuel requirements ?

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With regards to normal fuel planning: legally you are required to land at destination with 30' of holding fuel at ISA conditions (commonly referred to as FINAL RESERVE) + ALTERNATE FUEL (required fuel for a missed approach at destination, diversion to alternate airport).

Some operators specify some conditions that allow pilots to use the ALTERNATE FUEL without actually diverting to the alternate if required.

These conditions may vary from certain weather and approach requirements to mere pilot judgement... it depends on the company.

I am not aware of any minimum fuel limitation for HYD cooling, but I'm not a 747 rated pilot.

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I believe that guys at Lufthansa know how to plan fuel and less than 10T is not a planning error, but how does it fit to above given fuel requirements ?

 

"A good minimum is ..." is language leaning more toward a recommendation than a required minimum.

 

Do you fuel up your car when it gets to 1/4 tank, or do you fuel up when the light comes on? Which way is right, which way is wrong?

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aha aha .. a good one Kyle.  got the picture of the crew needed to get some fuel to continue the flight while thumb in the air ...

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In the PMDG Manual it is stated that 747 needs to keep min. 13608kg of fuel only for the purpose of cooling hyd. pumps.

 

I have to say that would be a new one on me, though I'm sure PMDG's source is impeccable. I can't find that figure (or any reference to hydraulic pump cooling being limited, or restrictions on hydraulic pump operation with lower fuel levels) in any of my 747 manuals, but I also don't know what the precise wording in the PMDG manual is (Kyle's post implies that it is a recommendation/someone's personal foible rather than a limitation).

 

As mentioned above, from a legal point of view you need final reserve (30 mins -- ~4.5 tonnes) plus alternate (depends obviously on where you're going). Circa 10 tonnes would be a fairly typical landing figure if the alternate wasn't too far away, but with a more distant alternate and/or any extra fuel could be over 20 tonnes.

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FWIW Mel liked at least 13T (circa 30,000lbs) at the threshold.... I seldom land with less.  

 

More is predicated on the destination, alternate, Wx, expected holding and a long list of other laundry items.  As fuel costs $ to purchase AND to transport.... the more efficient the dispatcher the better he is liked by the company.... until something goes wrong... then all the fuel in the world seems like a very sensible decision.  There are MANY ways to skin this cat....

 

HTH

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Try it out, intentional do not set the ENG/TANK configuration and continue to drain from 2 & 3.  At some point you'll get hydro messages. Note the level in the tank.  This is your minimum.

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A little confused especially about Kyle answer - if there is some fuel requirement coming from technical aspect ( like cooling ) which may be essential for lifetime of specified components, then in my opinion there is no decision freedom. 

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Yes I've been confounded over what to consider the minimum fuel needed for cooling, in the manuals it's the 13,000kgs and on other sources around 6,000kgs. 

 

-Angelo

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One thing to remember about fuel reserves is it cost money to tanker fuel.  Basically it takes one pound of fuel to carry 6 pounds of fuel. Some of the things I've used in my carrier are what we called in the military "island reserves" and also "redispatch" which can save fuel if the weather cooperates.  

blaustern

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"minimum fuel" should be looked at from two independent viewpoints.

1) approved fuel planning requirements

2) airplane technical system requirements

As far as #2 goes, the limiting system is hydraulic pump cooling (min approx 7T) followed by fuel pump operation (min approx 6T) respectively in a low fuel situation.

In my opinion, hydraulic problems will be latent, occurring not immediately. Fuel pump problems will be more immediate and obvious.

What you probably saw was the LH crew enter the reserves according to #1 (approved fuel planning requirements) which doesn't take into account #2 (airplane technical system requirements).

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On 2/3/2017 at 8:15 AM, Beardyman said:

In the PMDG Manual it is stated that 747 needs to keep min. 13608kg of fuel only for the purpose of cooling hyd. pumps.

As far as hydraulic pump cooling is concerned there are no specific limitations laid down on the minimum amount of fuel required in the B744’s Flight Manual. Although PMDG’s statement might still be true for some operators (I don't know if it is or not), airline experience over the years has shown that it is not necessary; just as the minimum fuel for departure was once set by some operators at 40,000kgs.

Simon and other members have already commented on typical minimum arrival fuel figures. However, in the case of the B744 a low fuel condition exists when the indicated fuel quantity in any main tank is 900 kgs or less. No pilot in their right mind would ever want to get into this condition, but even if he or she did end up flying on fumes with such a low fuel quantity, there is still no mention of hydraulic pump overheating problems in the relevant ‘Flight Operations with Low Fuel’ procedure. Needless to say, if they actually lived to tell the tale they would almost certainly end up spending the rest of what would have been their flying career firmly sat behind a desk - or in a penitentiary!

On a happier note, the definition of excess fuel is the amount of fuel left behind in the refuelling bowser, or alternatively, the fuel coming out of the wing’s overflow vents!

Bertie Goddard

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Then PMDG must be a bit more careful with data given in their manual, cause some people actually read those and take seriously :-)

 

Interesting fact about departure fuel ( 40T), from where it came Bertie ?

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16 hours ago, Copper. said:

As far as #2 goes, the limiting system is hydraulic pump cooling (min approx 7T)

Since 747 normally lands with equal quantities in the respective mains, I'd like to correct my statement and say min fuel for hydraulic heat exchanger coverage is approx 10T.

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