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Richard McDonald Woods

Using long range cruise

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When I use the LRC mode in PFPX to plan my long haul flight, I am not sure what to specify as my cost index in the FMC.

 

Lacking any form of conversion table, what should I specify?

 

 

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Lacking any form of conversion table, what should I specify?

 

LRC and CI are competing concepts.  They cannot exist together.  If you really want to use LRC (which is static, and will not adjust for flight factors, so it's not as cost-competitive as CI), you can use the conversion table from Boeing:

http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_05_3.html

 

...and then change from ECON to LRC on the cruise page.

 

From Boeing, directly:

It is very important to note that the LRC speed is almost universally higher than the speed that will result from using the CI selected by most carriers. If faced with a low fuel situation at destination, many pilots will opt to fly LRC speed thinking that it will give them the most miles from their remaining fuel. As shown in figure 2, the best strategy to conserve fuel is to select a very low cost index, with zero providing the maximum range. Any pilot can easily demonstrate this during cruise flight by inputting different CIs into the FMC and comparing with LRC by observing the predicted fuel at destination.

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Many thanks for your research, Kyle. Although a regular reader of Aero magazine, I haven't gone back as far as 2007.

 

So I shall stop using LRC altogether, and use a CI of around 120 (mid-airline value) in future.

 

I must say that with a variety of CI values/LRC, and sometimes using re-dispatch, I am still getting significant fuel remaining figures. These are often in the 12-15 tonnes range.

 

Without a great deal of work (re-flying the routes, obtaining the same wind conditions, etc.) it is not easy to determine why the fuel remaining is high. That said, I have heard that some airlines expect their captains to land with values in excess of 10 tonnes.

 

Cheers, Richard

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Without a great deal of work (re-flying the routes, obtaining the same wind conditions, etc.) it is not easy to determine why the fuel remaining is high.

I have found that on a seven hour flight I normally land with around 8 tonnes. I flew OMDB to KBOS (a real Emirates 777LR flight) which was approx thirteen and a half hours and I landed with almost 11 tonnes. Of course the one major difference is the 5% contingency fuel so with a flight twice as long that will double. AS PFPX seems to be pretty accurate I seldom burn the contingency fuel. That with say improving weather etc could explain some of the difference. If you include SIDS and STARS in your PFPX flight plan then the fuel used in flying them will be included. I normally plan the flight with a SID and a STAR, note the fuel and then replan omitting the SID/STAR again noting the fuel, I then plan again without a SID/STAR but this time I add in the extra fuel from my SID/STAR plan and a touch more to cover carrying the fuel. If you then get vectors this can shorten the distance flown and will save some fuel. 

 

In summary I have found the amount of fuel remaining increases with the duration of the flight.

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@Nixon,

Thanks for your comments. I would expect FREM to rise with the length of the planned flight. I also thought that re-dispatch was a major contributor to reducing the high FREM need.

 

@Brian,

Many thanks for your link re CI. It's a very interesting article.

 

Thanks to both,

Regards

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You worry about fuel conservation with simulated fuel!?

Its discipline. Its like making your bed even if you live alone lol

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I've an additional question: why it is labeled LRC (Long Range Cruise) and why is it left in the fmc when CI values gives better mileage? Does any carrier fly LRC? When should a pilot select LRC?

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Stefan,

That's a good question because it has always implied to me that LRC is a way of minimising fuel usage. But I have been proven wrong - it is the opposite because the range of normal CIs gives you a better burn!

Cheers, Richard

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You worry about fuel conservation with simulated fuel!?

Depends on how you use the simulator. At times, I've used it to practice things that I learned in my dispatch course, in which case, yes, I would.

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if ever you've flown into JFK (in real world)  on a heavy 744 or 777,  and they mess around changing runways on you 4 or more times on approach which  causes go-arounds and diversions you'd understand why airlines ask them to carry 10 tones arrival fuel.  Saves on buses and coaches for 300 pax from KEWR... 

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I've had success reducing cruise speed to 0.80M to improve my fuel remaining estimate, for example unexpectedly hitting the Southern jetstream on the way into YSSY (that's an interesting situation even in a simulator). I was wondering why LRC wasn't the same as maximum endurance too, and the Boeing publications referenced earlier helped somewhat and reinforced how complex a task planning and execution are in these big machines.

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Hi Dan, good to hear from you!

 

Perhaps that was what I experienced recently going into YSSY from VHHH. On descent I was surprised at the sudden strong turbulence (ASN) and had difficulties controlling the aircraft for an approach to 34L.

 

Of course the jet stream would only have accounted for the high altitude turbulence, but I was proud of my abilities to cope with all that was thrown at me.

 

Regards, Richard

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Hi Richard, I will occasionally use SkyVector with satellite wx and wind barbs enabled (see Layers options) to see significant weather while oceanic. It takes a few minutes to enter the flight plan but when doing so there's not much need to enter every waypoint as long as you can select a point within several hundred miles of your enroute location. My flight was a very fictional KIAH-YSSY, which in the -200LR is well within range (assuming ETOPS330) but stretching the limit of the -300ER that I tested on this trip. ASN enroute winds were not as close to actual simulated as was SkyVector thus the surprise.

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Still waiting for Kyle or Rob or someone other to give us some info about LRC here... :-)

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I appreciate the vote of confidence.

 

Remember that aviation is constantly evolving, and we occasionally carry old methods into new realms of technology for familiarity's sake.

 

Case-in-point: VOR and NDB approaches.  Even though most fleets and even GA aircraft have some form of IFR-approved GPS, we keep these things around.  They aren't usually used, but they're still there.

 

Same thing goes for LRC (and MRC for that matter).  CI came as an evolution of those concepts, because it takes into account wind among other factors.  If the air were completely still, LRC and MRC would give you max range values, but the air isn't still, and there are other factors into flight costs.

 

Note the bolded and italicized text over the graph in this article:

http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_05_2.html

 

(It's also worth reading the article.)

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Thanks for clarification Kyle. So summed up: you'll never use LRC but instead enter CI 0 if you have massive fuel problems.

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Thanks for clarification Kyle. So summed up: you'll never use LRC but instead enter CI 0 if you have massive fuel problems.

 

That's the guidance I've seen from Boeing, and they're the ones with the data to back up the claims, so I'll gladly listen to them...haha

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if you have massive fuel problems.

Could you indicate an example of "massive fuel problems"?

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Could you indicate an example of "massive fuel problems"?

 

My understanding was that he was referring to having a shortage of fuel at the destination, given the current CI.

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Could you indicate an example of "massive fuel problems"?

 

I do not know if this is realistic but let's assume you've calculated much too optimistic (low cost carrier) and get some stronger headwinds and also a forecast of some holding's because of bad weather. I can imagine you'll try to set CI to 0 if it is possible to not do an extra fuel stop.

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I can imagine you'll try to set CI to 0 if it is possible

 

 

When I do the planning with PFPX I use a CI of 20 for the LR and 40 for the freighter. PFPX wind forecasts seem reasonable so I never have encountered a fuel issue. I will try switching to CI 0 midflight sometime and see how much that increases the reserve fuel. Thanks.

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