[PFPX Profiles By FlyPrecisely]

This time with missing picture!

 

[PFPX Profiles By FlyPrecisely]

Hello Mykyta and Duarte,

 

I was also interested in the answer to this question regarding the higher fuel consumption vs. the PFPX estimate. I had a quick look at the detailed information Duarte provided for the flight and note the following which might help explain the variance.

1. I plotted the fuel balance by waypoint for the actual flight and PFPX estimate (see chart below).

1. The chart shows the fuel burn up to KOMUT is pretty close. Thereafter you can see actual fuel burn increases viz. PFPX.
2. I noticed in the PFPX OFP that the mach speed is .78 at TABAX and KOMUT, but then it starts to decrease to .74 by TIMTO. If the actual flight was flown at constant .78 this could explain the increased fuel burn after KOMUT. It's could also be a conversion issue with how Cost Index 35 translates to TAS/M# in the Aerosoft FMC logic v. what's in the PFPX profile.
3. The average fuel burn (ie kg/hr) for the cruise portion of the flight was around 25% higher than predicted by PFPX under similar weight and OAT conditions. Other than the speed issue noted above, it may be that the Aerosoft bus fuel burn is not modeled so accurately (ie as a function of weight, OAT, etc).
4. I also noticed that the actual flight commenced descent well before the TOD point in PFPX (ie at TIMTO the actual flight was at FL252 whereas in PFPX it was still in cruise at FL380 at this point). Also the flight log shows a very strong wind of 101kts at TIMTO which is higher than the PFPX profile. A longer, slower descent would add to the fuel usage especially if there was more low level maneuvering than what PFPX assumes for the descent profile.

Anyway, hope this is helpful in the analysis!

Kind regards,

Michael.

[PFPX Profiles By FlyPrecisely]

Hi Mykyta,

Thank you! Really appreciate your efforts in making these profiles.

 

Cheers,

Michael.

[PFPX Profiles By FlyPrecisely]

Hi, Michael.

I use separate ISA conditions when the OPT/MAX altitudes differ from the ISA ones. When they don't I use an adjustment ±x% to the fuel flow per ±1̂0C. The stock PFPX profiles have the same situation.

Some people noticed the same thing here. http://forum.aerosoft.com/index.php?/topic/95939-isa-deviation-in-evaluate-option/

Looks like a PFPX bug. However, there is no idea whether it affects the calculations too much. I could recommend to use a manual fuel adjustment (extra fuel or so) according to the average ISA deviation. On Boeing 747-400 and 767-300ER it is generally ±3% per ±10C deviation. Just apply this percent to your cruise section fuel.

The list of my profiles that have ordinary adjustments:

– Boeing 737CL Family

– Boeing 767-300ER Family

– Boeing 767-300ERW Family

– Boeing 777-200LR/-300ER

The remainder of the packages have various ISA deviations.

Regards,

Mykyta

Hi Mykyta,

thanks, I hadn't spotted the other thread regarding this topic. It seems the developers are aware of the issue so will await their fix.

Regards

Michael.

[PFPX Profiles By FlyPrecisely]

Hi Mykyta,

Many thanks for the very detailed additional aircraft profiles for PFPX, especially the latest ones for the 747-400. However, I have a question: do your profiles adjust for non-ISA conditions?

I just planned a flight from KSFO-EDDF using your 747-400 PW4056 profile with a M.84 cruise, but I noticed in the OFP printout that the TAS at FL390 remained constant at 482 knots although the temperature deviations at this cruise altitude ranged from ISA+15 to ISA-1 so there should have been some variation in TAS (typically 1k change per 1 degree deviation from ISA).

Thanks again,

Michael.