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?

 

 

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.

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

 

 

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.

Here's a link to the full series on fuel conservation in a single pdf.



http://www.boeing.com/commercial/aeromagazine/articles/qtr_02_10/pdfs/AERO_FuelConsSeries.pdf


Brian

Excellent link Brian, thank you!

@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

You worry about fuel conservation with simulated fuel!?

Hi Bren,

All part of my experience. Sad? Or just trying to keep on learning.

Cheers

You worry about fuel conservation with simulated fuel!?

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

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?

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

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.

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... 

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.