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stretch1365

trip fuel and safety margins

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Hi all,

 

I have been flying the 747-400 alot lately, actually replicating Iron Maidens, Book of Souls World Tour, which is taking place at the minute, and thoroughly enjoying the experience.

 

So I have a question and wonder if any of you fellow pilots out there might have an answer.

 

The latest leg I have just completed was from Perth WA YPPH to Cape Town, South Africa FACT. A great circle distance of around 5400 sm, 8690km, taking 10 1/2 Hours, and it did too. Anyway I have been using a ZFW of 237.1kg for all my flights just to keep things constant and used topcat to calculate the expected fuel requirements, yes I know it is not 100% accurate but it is pretty close. Anyway I forget the actual suggested fuel requirements somewhere around 120 000kg which I upped to 140 000kg simply because there is no diversion airfields on this route, well there is no land so it is difficult to divert really, but I thought 20 000kg of extra fuel would be ample! Unfortunately I was faced with a 100/120kt headwind all the way across the ocean which used more fuel than expected and I landed with no more than 4800kg of fuel in total, instead of my estimated calculations of 20 000kg, which I think is cutting it very fine indeed.

 

Now I realise that having started out with extra fuel means the aircraft was heavier, which means the fuel consumption will be higher to start with. After the flight I looked up on the net the true figures for a Boeing 747-400 which suggested 11.11kg/km which works out at a fuel load of 115 000kg roughly, far lighter than my 140 000kg in the sim.

 

So my question based on this journey is what would be the safe extra fuel requirement or contingency required on this trip over and above the original 120 000kg fuel load? Also can anyone tell me what is the usual remaining fuel quantity upon landing at the destination?

 

Thanks for any answers to my questions, sorry if the question is a bit long winded but there are alot of factors to consider. I had forgotten quite how much fun the 747-400 could be, and this tour sure has rekindled my interest in the 747-400 and I look forward to the new 747-400 v3 when it arrives.

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There is never a set amount of contingency fuel. It depends on atmospheric conditions ans weather for the particular flight, chosen curise speeds and cruising flight level and other things. The amount of fuel at the gate is the same way. On domestic hops in any airplane on a flight that doesnt require an alternate, i plan 45 minites of reserve fuel and 15 minutes of contingency fuel. If the wx is bad, ill throw on another 30 minutes.

 

Thats all i can tell you for now. I based my answer on what i fly at work and what i use for the NGX when i play p3d.

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you might want to look into using a flight planner that can take winds into account. for short hops estimating your burn by km/kg is probably fine but as you discovered the inaccuracies will increase quite a bit over long ranges and real fuel planners will take into account how the burn rate changes as you get lighter in addition to meteorological factors.

 

simbrief is free, fairly easy to use, and i think you might enjoy seeing how you can get a much more accurate picture of your fuel planning..  it's at simbrief.com

 

edit: i plugged your route into simbrief just out of curiosity and it had a suggested fuel of 173,336kg at flight level 370, it actually suggested a lower flight level of FL240 having a burn of 163000kg .. the weather may be a bit different now than when you did your flight also.

 

for contingencies there is also ETOPS stuff to consider on long flights like this which is a pretty deep topic but basically includes making sure you have fuel to reach the various airports along the route you might need to divert to even if they are a few hours away. i think PFPX is the only planner that really supports that stuff..  might be overkill for what you are trying to accomplish at this point but it is also a fascinating subject.

 

cheers

-andy crosby

 

edit: technically with a 747 it's LROPS or EROPS maybe ...i'm not sure what the proper acronym is when it's a 4 engine plane

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As mentioned above, particularly for a long haul flight you really need to take the wind in to account when planning your fuel load.

 

From a regulatory point of view, you are required to load trip fuel (takeoff to touchdown) plus a contingency figure (usually around 5% of trip fuel), plus fuel to reach your alternate from your destination, plus final reserve fuel (30 minutes at 1500ft - around 4800kg in the 747) plus fuel for the taxi out (figure around 200kg/min in the PMDG 747) and any extra fuel as required by the commander (e.g. for holding etc). ETOPS is not applicable to the 747 BUT there may occasionally be a decompression fuel requirement (to reach an alternate in the most limiting scenario, usually a 2 engine-out decompression (which would necessitate flying at FL100).

 

You must land with at least your 30 minute final reserve intact - if it appears that you will be landing with less then this then you must divert to a nearer aerodrome and/or declare an emergency. Normally, of course, you will be landing at your destination with final reserve + alternate fuel - so in the 747, depending on how far your alternate is from your destination it would be fairly common to land with around 10t in the tanks.

 

Bear in mind that the PMDG 747 burns quite a bit more than the real thing - I would figure on around 12t/hr as a rough estimate, and/or set the Simbrief fuel bias to P8.

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It’s still ETOPS (ExTended OPerationS).  Rules still apply to tri and quad passenger aircraft. One difference however is that it only applies past 180 minutes from an adequate airport.  The 747 sees a little benefit here since the one engine inoperative cruise speed is better than that of a twin. It’s also important to point out that ETOPS is about more than just engines, in fact diversions for non-technical reasons are far more frequent than an engine shutdown. 

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Thank you for all the answers to my original post.

 

Spesiman, I found your answer especially useful as I do use Simbrief already, although mainly for planning the actual route, I haven't tried it for fuel planning as yet, as I have always used Topcat, but I think I will look into this aspect of Simbrief again.

 

As my normal flights tend to only be a few hours max I haven't really had to plan in a wind factor on most of my flights before, and to be honest this long flight I did really caught me out with the weather, so something to take into account on long flights in the future.

 

Skelsey you said you aim to arrive with 10000kg of fuel at your destination, which by coincidence is close to my made up figure, as I have been trying to arrive with about 13000kg so far on each leg of the tour.

 

Anyway thank you for your information all, I think I might look into this fuel planning more closely for the next long leg of the tour.

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 I do use Simbrief already, although mainly for planning the actual route, I haven't tried it for fuel planning as yet, as I have always used Topcat, but I think I will look into this aspect of Simbrief again.

 

 

oh, hahaa! you have 99% of the steps done then :)  just change the ZFW dropdown to your intended weight and make sure it's the proper airplane selected..when you generate the plan, in the pdf file it makes.. all the numbers are right there. i use the LIDO format usually and it lists it like this...you can see the trip, 5% contingency, alternate, 30min extra, and taxi..also a spot for if you specified extra in the planning 

 

cheers and good luck with the next leg of the tour

-andy crosby

---------------------------------
PLANNED FUEL 
--------------------------------- 
FUEL             ARPT   FUEL TIME 
--------------------------------- 
TRIP              EMA  20867 0353 
CONT 5%                 1330 0015 
ALTN              LHR   2780 0026 
FINRES                  2208 0030 
--------------------------------- 
MINIMUM T/OFF FUEL     27185 0505 
--------------------------------- 
EXTRA                      0 0000 
--------------------------------- 
T/OFF FUEL             27185 0505 
TAXI              TFS    500 0020 
--------------------------------- 
BLOCK FUEL        TFS  27685

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Further to BrianW’s reply, ETOPS means Extended Twin Operations and those rules apply to approved two engined aircraft and their crews; not the B744.

 

Contingency fuel is that part of the initial fuel load which is carried to cover unforseen circumstances from the planned flight, so it is not the amount you hope to have left in the tanks at your destination. Contingency fuel is normally based on 15 minutes holding clean at the planned landing weight or 5% of Trip Fuel, whichever is greater. However, this also depends on the availability of a suitable en-route alternate, in which case the 5% can be reduced to 3%. It can also be reduced at the Captain’s discretion if there is a late increase to the planned Required Fuel.

 

Calculate your total Required Fuel using Simon Kelsey’s reply here as a guide and aim for 10,00kgs as a minimum to land with. However, if all goes according to plan then you can expect to have at least your diversion fuel + Reserve (+ any additional fuel carried, if required) plus most of your contingency fuel remaining overhead your destination on a good day.

 

There are numerous other flight planning considerations which can affect your decisions and the amount of fuel you need to carry on long-range B744 operations. For example, if no destination alternate exists then you will need to carry Island Reserve and calculate a Point of No Return (PNR). Incidentally, if you fly the return leg from Capetown to Perth then ‘Aussie Rules’ will need to be taken into account at the planning stage when considering the forecast weather and your fuel requirements.

 

So yes, Dave, there are a lot of factors to consider in real life and it is all too easy to get caught out by the weather or other operational factors if you don’t remain vigilant and plan ahead. Landing with only 4,800kgs in your tanks was cutting it very fine indeed, because this amount is equivalent to landing with only Reserve Fuel remaining (i.e. 30 minutes holding clean at 1500ft). This is the absolute minimum remaining in tanks at landing and it is not a comfortable feeling – even on a good day!!

 

Enjoy your PMDG B744 flying.

 

Capt Bertie Goddard (Berts)

B744 IRE/TRE (Retired)

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Further to BrianW’s reply, ETOPS means Extended Twin Operations and those rules apply to approved two engined aircraft and their crews; not the B744.

 

 

I don’t just make this stuff up trust me B)  Prior to 2007 that was indeed the case.  In the FAA world ETOPS has since been changed to the new acronym and restrictions for aircraft with more than two engines added. ICAO calls it EDTO, and EASA uses LROPS, but most authorities are still using the term ETOPS for both. In reality the 180 minute rule is suitable for almost all routes other than those in the southern hemisphere so most operators wouldn’t notice a change.

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Ah well, I said there were a lot of factors for Dave to consider! Unfortunately, some factors can be more confusing than others and it would seem that the acronym ETOPS, or rather its different interpretation by the three main regulating bodies ICAO, EASA & FAA, is clearly one of them!

 

If Dave wants to read all about ETOPS rules, he might be interested in an excellent presentation given at a meeting of the ICAO Regional Aviation Safety Group in 2011 by Eric Fortunato, Airbus Head of ETOPS/LROPS Programs Product Integrity - Engineering Directorate. In it he clearly states that under EASA rules (which I operated under) ETOPS means Extended Twin OPerationS and is applicable to twins only, whereas LROPS (Long Range OPerationS) is applicable to Tris and Quads only. However, BrianW is also correct when considering FAA rules – hence the confusion.

 

ETOPS (no matter what its acronym actually stands for) is all about managing flight safety and risk because, unlike flying long distances on 3 engines in a B744 which is usually relatively straightfoward, having to fly on 1 engine for 180 minutes in a twin over inhospitable terrain in order to land at the nearest suitable alternate will definitely focus the mind of every pilot! Incidentally, the presentation can be found at:-

 

<http://icaonacc.org/Meetings/RASGPA/RASGPA4/Presentation1Airbus.pdf>

 

 

Bertie Goddard

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