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aceridgey

PMDG 777-300ER underburning fuel?

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Hi guys,

 

I connect PFPX with ASN and regularly update and cross check remaining fuel against the flight plan.

 

In the year or so since the 777 has been out, I have never seen the 300er close to predicted fuel left. It's always underburned over the course of a flight with a gradual scale in the cruise.

 

For example a flight I've just done took off with 200kg more fuel than predicted

 

3 hours in ; 1.5tonnes

 

6hours 2.5 tonnes.

 

 

Can anyone look into this for me and see if they're getting the same results in the 300er?

 

(Please use accurate weather such as ASN)

 

Alex

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I have not run trials with the 777-300ER and PFPX for this purpose (I did with the 777-200LR); however, I have flown quite a few long hauls in her with the AA colors.  The VHHH-KDFW is one I've done several times, and I have not noticed a significant variance between planned and actual fuel burns.  There is a variance, to be sure, but I am not seeing any that raise an eyebrow.

 

A flight should be flown repeatedly, each time varying just one variable, to have a demonstrated problem.  As Michael pointed out, many many flights have not yet exposed a problem of any significance.

 

It's worth identifying what might be considered significant.  If my actual trip burn is within 5% over a long trip then I'd consider that an insignificant variance. If the variance is >5% then you need to look at the difference in planned trip time verses actual and in all cases I've seen the trip took longer which means more fuel burn.  For a 200,000 lb fuel load, that means I wouldn't consider a variance of 10,000 lbs or less significant.  If you're off a ton is that really significant?

 

As inferred earlier, I have run these fuel burn trials in the 777-200LR in the past year with PFPX and ASN on flights >8hrs and I never saw a pattern in the actual fuel burns.  Sometimes actual numbers were so close to planned that it was interesting.

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Hi,

 

Also for your knowledge, in PFPX you can assess and modify the fuel consumption of the profile of your aircraft while airborne. If you feel that the fuel calculation in PFPX doesn't match what you experience, then check the values in the profile. I'm not home so I don't have access to my computer to give you the exact reference but you will surely find it.

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