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Hi,

I know this is PMDG (so as real as it gets!) but I'm quite surprised of the time it takes to refuel the 747. I'm currently at YSSY with the -400 loading fuel for a 14h flight to Johannesburg and the time req. to load 156.1T (uplift fuel) is 1h43 + 7:30 to hook.

IRL, is it so long?

And second question, in this case, do the crew join the aircraft 2h before the departure or does the refueling start before the crew arrives on board?

And it also means that the amount of fuel required for the flight is also blocked and requested at least 2-3h before the departure well before the actual amount of pax is confirmed (event though I know that airlines have statistics for each flight).

Is it all correct?

Thanks.

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Depends on the facilities to a large extent. A modern 747 has 8 points on it (refuelling nozzles) through which you can shove fuel into the thing, and it can hold a bit shy of 60,000 US gallons. Depending on the refuelling equipment, you can transfer fuel at anything up to about 500 gallons a minute per nozzle (that's with super-duper modern equipment which pumps at fairly high pressure). So that means a maximum fill rate of 1,000 gallons every two minutes for every nozzle, so just using one fuel line it would take slightly less (since its capacity is a bit less than 60,000) than 120 minutes to fill it up from completely empty. But since it has eight nozzles, theoretically you could fill it up from bone dry to full in just under 15 minutes if you were bonkers enough to have eight fuel lines connected to the thing, this is not including the time spent connecting the fuel lines, etc, sorting out any paperwork, any comms or anything like that involved in actually getting the fuel amount sorted before you actually start transfering fuel. There are other things which can slow it down a bit too, such as you have to be careful about static electricity and other stuff when connecting fuel lines, rather than just ramming them on there if you don't want the thing to explode.

With big aeroplanes at a typical modern large airport (with underground fuel storage at the stands instead of tankers), it's probably typical to use two nozzles per wing (so you can upload fuel at anything up to about 2,000 gallons a minute with the best equipment, although whether they would actually run the pumps at full throttle like that is another matter, since it's not like you are doing a formula 1 refuelling pit stop, and it would depend on where you were too; at a UK airport, everyone will have to stop for a tea break halfway through the proceedings lol). Of course it would be very rare for a 747 to be run completely dry, so you are unlikely to be shoving over 59,000 gallons of fuel in there, although if you do and you are collecting the coupons like at a normal garage where you fill up your car, you'd definitely have enough coupons to get that garden patio set, and remember, if you are buying that much fuel (it will cost well over 160 grand to fill up your 747 to the brim from empty) and they don't bother to wipe down your windscreen, then you should complain. :laugh:

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Hi Alan,

Nice explanations, thanks!

In my case, I'm used to landing with around 15T of fuel. For the flight YSSY-FAOR, I have a calculated fuel quantity to load of 171T (minus 15T = uplift 156T) accounting for alternate enroute airports in case of emergency (there is not many airports in south Indian ocean!).

I guess the PMDG ground ops system uses only one line for refueling.

It would be great to allow the use of more lines to fasten the process a bit.

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You should bear in mind for realism, that it's actually not that uncommon for big jets to 'tanker' fuel around based on their destination, since some places around the world are considerably more expensive to buy fuel from. This used to be a lot more common years ago when fuel was a lot cheaper, when they were not bothered about the downsides so much, since carrying more fuel than you need for a flight can limit the ceiling and that will in fact cause you to burn more fuel, but it does still sometimes work out cheaper to carry fuel to somewhere even with that happening so it really does still go on, even if it is only to the extent of carrying a bit to at least save some money. One US gallon of jet-A is about 1.75 in the US (varies depending on where), whereas it can be considerably more expensive in some out of the way places in the third world, unless it happens to be an oil producing nation with refining facilities too.

As you probably know, the 747-400 will often make step climbs because of the fuel it is carrying, i.e. going across the Atlantic, a 747-400 might initially climb to 37,000 feet and wait until it has burned a bit of fuel off before going up to maybe 43,000 feet or whatever, since it might not be able to make it up there initially at a suitable speed, and generally speaking, the higher up you go, the better the tailwinds usually are. If you like ultra-realism, you can actually look up online how much jet-A is at various places around the world and factor that into your virtual flight planning and your climb profile, although we are in the fortunate position of not having to pay for fuel in our sims (unless you use something like Air Hauler, in which case, you do have to 'buy' it).

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I don't really mind about fuel costs so I don't usually bother tankering fuel. From a pilot's standpoint, I try to calculate fuel so I keep close to the minimum landing fuel with a safety margin based on the EU-OPS.

Also tankering depends vastly on the ZFW (which in turn also depends on the max fuel you can load and the fuel required with regards to the distance of flights and winds) and the difference between the ZFW and max LW.

On the 747-400 you can still land with 39T at full ZFW without busting the max LW, but on the 77L you are limited to 14T.

I understand the concept of tankering fuel but I think it is more a think of dispatchers than pilots. 

I saw some payware videos where the pilots confirm the quantity of fuel to load for the flight and decide which extra they want before the refueling is requested but I have not yet seen a video with tankering fuel.

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Hi Al,

 

Would you be able to comment on the OP's other questions about when the flight crew might arrive (eg 2 hours early for a large fuel to load)?  I would suspect the dispatcher would have a rough idea about the fuel load, get the loading started, and then a final on-load or off-load in conjunction with the pilots after ZFW is finalised and the time is closer to departure?

 

Romain, great questions! :)

 

Regards,

Subin Jacob.

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This discussion ignores the delivery system that is buried under the ramp, the thousands of meters of pipe and the flow rate of the system when a dozen aircraft are fueling.  Your equipment on the ramp refueling the aircraft is not drawing fluid from an infinite reservoir. There is a significant amount of mechanical engineering that goes into these systems. It's a good thing to have an appreciation of that.  I'm electrical not mechanical so I don't have an answer, but 500 gal/min at the nozzle seem like it would require a pretty high velocity to get that from a fuel line that is what... 4-in?  A quick look at the engineeringtoolbox.com source indicates 260 gal/min maximum for 4-in at 6.6 ft/sec for water in a steel pipe.  Water is heavier so flow/velocity might be higher but it's not a steel pipe so head losses are higher.  I dunno.

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I have read that on long-hauls they often pre-fill to within 80% of expected fuel load, even if the crew have not arrived, and do the final fill once performance and loadsheet are locked down a bit more. From memory, Virgin Aus fill their 77W to a certain level and then park them on the remote stands for 8 hours or something before the return flight.

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That's make sense. It's a good way to save time at gate (I guess fees must be higher at a gate than at a remote parking) and the "prefill" level is calculated in such a way that it cannot exceed the required fuel quantity for the next flight.

 

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3 minutes ago, Budbud said:

That's make sense. It's a good way to save time at gate (I guess fees must be higher at a gate than at a remote parking) and the "prefill" level is calculated in such a way that it cannot exceed the required fuel quantity for the next flight.

 

Here is the article, it is a bit techy but quite interesting:

http://www.infinidim.org/calculatedtotalizer-fuel-pre-fuelling

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Hi Wes,

Thanks for the link. Very interesting article indeed and full of great information!

It answers somewhat to my questions. However, it seems that pre-fueling an aircraft is not that common at least on the T7 as the author says they couldn't identify other companies doing this (or does he mean other companies that pre-fuel AND sit the aircraft? Not sure whether to interprete if they searched for the conjunction of both conditions...).

 

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17 minutes ago, Budbud said:

or does he mean other companies that pre-fuel AND sit the aircraft?

Looks like that's what he meant.

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8 hours ago, Budbud said:

IRL, is it so long?

And second question, in this case, do the crew join the aircraft 2h before the departure or does the refueling start before the crew arrives on board?

And it also means that the amount of fuel required for the flight is also blocked and requested at least 2-3h before the departure well before the actual amount of pax is confirmed (event though I know that airlines have statistics for each flight).

Is it all correct?

Thanks.

It sounds a bit long and as others have already confirmed there may be ways of speeding it up but it's a lot of fuel...

We report 1:30 before the flight and usually have our fuel decision in the system about 10 - 20 minutes later, assuming no major issues. They will start refuelling well before we get there.

There is normally a 'plan' available in the system a few hours before the flight with an estimated ZFW and total fuel, they will start refuelling to about 5 tons below that figure awaiting our final confirmation. They are normally still refuelling (and nowhere near that amount) when we get there so we often personally confirm the fuel load to them and they adjust accordingly.

Our ZFW isn't finalised until during taxi out, everyone works to an estimated ZFW which appears to be worst case, it usually goes down or maybe up by a ton or so, rarely up by enough to really change anything though.

Refueling isn't something we get too involved in, providing they give us what we want in the right tanks, we're happy.

Hope this helps,

Ian Webber

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5 minutes ago, iwebber said:

Hope this helps

Hi Ian,

Greatly, thanks! :happy:

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A modern 747 has 8 points on it (refuelling nozzles) through which you can shove fuel into the thing,

Speaking of YSSY operations...  Mostly, only 2 underwing nozzles are used (left hand side). For longer haul flights, both left/right wing fuelling nozzles are used for a majority of the refuelling period to speed up the refuelling process. The only other way to get fuel into the aircraft is by overwing points. The overwing refuelling method is only used if underwing refuelling is not available. After 2/3rds or so fuel uplift, the second refuelling truck usually disconnects and goes off to another aircraft, leaving one truck to finish off the process.

At YSSY, prefuelling is a normal procedure. Refuellers know where the aircraft is going, so they load an amount of fuel which would be an absolute minimum to get to the destination (with a strong tailwind). Closer to departure time, they are given a more accurate fuel amount, usually before the pilots have reached the aircraft. When the pilots arrive at the aircraft and make their final calculations, they tell the refuellers if  that fuel is ok, or whether they should load more.

Tankering is extremely wasteful. For every extra kilo/pound of fuel you carry around with you, you have to add a large amount of extra fuel just to carry that tankered fuel. It's rarely cost effective. I've only seen it done when the refuellers have gone out on strike at a particular airport and fuel cannot be obtained there.

As an engineer, I would want to be at the aircraft at at least 1.5 hours before a flight to give the fuellers the prefuel amount. If refuelling took any more than 1hr 15min, there would be lots of nervous people around the aircraft :P. Note that some airlines (including JAL) want all their fuelling to be done prior to boarding, so timing is critical, especially if there are short turnaround times.

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