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lassekronborg

Updated tool for 737NG performance planning

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Hi Zachlog,

 

Thanks for your report! Maybe you could telle me a bit more about the planning.

 

What 737 variant did you fly? Did you plan using the same aircraft variant? Did you enter wind information in your plan but not in the FMC? Did you use the same flight altitude in the planning tool and in the FMC? Did you enter the correct flight plan distance which might be longer than the point to point distance? Did you use the same cost index setting? Were you using the same Gross Weight?

 

These factors might explain why you see differences from the tool and the FMC but....

 

...Did you try to fly and see if either the tool or the FMC came closest to the real fuel consumption for that flight?

 

Cheers

Lasse

Hi Lasse,

 

Here is some more information:

  • Aircraft: Planned for and used the 737NGX-800 WL.  I do not fly any other variant.
  • Winds:  This could be one of the issues.  I entered the runway winds in both the plan and in the FMC/TAKEOFF page.  I did not enter in the FMC the wind/wind direction specified in the box in the plan with the flight level data.  This wind/wind direction is not highlighted in yellow...does it have to be entered in the FMC and if so where ?
  • Altitude:  Used the same altitude in the plan and the FMC/PERF INIT....FL300.  One observation.  The plan has optimum FL316 but even In the beginning of the flight and still heavy, after reaching FL300, the optimum level in the FMC/CRZ was FL340.
  • Distance:  The computed distance in the plan is 2146 NM, the route I used in FSBUILD to create the flight plan yielded a distance of 2170 nm (without the SID/STAR), I specified a distance of 2200 nm  in the plan.
  • Cost Index:  The same in the FMC and the plan......20.
  • GW:  This is where I was the most careful to use the exact same no. of passengers, cargo and fuel load in the plan and FMC.  I don't remember the exact GW but the ZFW in the plan was 131988 lbs, the FMC computed a ZFW of 131.8 x 1000....very close.  The fuel load in both the plan and FMC was 42752 lbs.  Regarding the fuel....the plan Landing Fuel was 9036 lbs, the FMC/PROG estimated fuel at KLAX 8.2 x 1000 after reaching FL300 and dropped to 8.0 x 1000 after climbing to FL340 (the FMC optimum).

I did not complete the flight so I cannot answer your last question but I am planning on redoing this long range (for the 737 anyway), fully loaded flight multiple times.  FYI, the maximum no. of passengers on the PMDG NGX800 is 162, not 172 as your documentation states (150 economy, 12 first class).  You may want to fix the documentation.  Also, if you would like, I can send you a PDF with the plan but I don't see an attach option in this forum; just let me know.

 

Thanks,

Zachlog


Zachary Kapsiotis

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If your route planner includes weather information and average winds, you can enter that right below where you enter your flight level in the FMC. If you planned the flight using a high tail wind factor you might end up with too little fuel aboard. But if you didn't enter wind in the sheet and also didn't do it in the FMC they are supposed to agree.

 

When I made the sheet and the calculations I qualified them by using both the FMC, other available fuel planners as well as some Boeing documentation. Never was any of those sources in agreement. So my goal was to be within 5 percent of the PMDG FMC calculated consumption while still observing the Boeing manuals and performance documents. In other words, the sheet will only rarely be 100 pct correct.


// Lasse Kronborg

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If your route planner includes weather information and average winds, you can enter that right below where you enter your flight level in the FMC. If you planned the flight using a high tail wind factor you might end up with too little fuel aboard. But if you didn't enter wind in the sheet and also didn't do it in the FMC they are supposed to agree.

 

When I made the sheet and the calculations I qualified them by using both the FMC, other available fuel planners as well as some Boeing documentation. Never was any of those sources in agreement. So my goal was to be within 5 percent of the PMDG FMC calculated consumption while still observing the Boeing manuals and performance documents. In other words, the sheet will only rarely be 100 pct correct.

 

Lasse,

 

I understand that there will be differences between plan and actuals and did not expect otherwise.  But to use the plan I needed to resolve the show stopper "Using RSV Fuel" thus my post for some help.  I will give it another try as soon as I have some time.

 

Regarding the definition of winds....I will add to the FMC as you suggest.  In this flight, the plan had a head wind of 50 nm out of 270 degrees.  While in flight, the observed wind on the PFD was 59 nm from 318 degrees.

 

Regards,

Zachlog


Zachary Kapsiotis

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Regarding the definition of winds....I will add to the FMC as you suggest. In this flight, the plan had a head wind of 50 nm out of 270 degrees. While in flight, the observed wind on the PFD was 59 nm from 318 degrees.
Without entries for wind direction/speed at TOC, waypoints where appropriate, and a descent forecast you are just spinning your wheels. See pages 131-143 of the PMDG 737 Tutorial 2 for information on where to get the winds and how to enter them into the FMC.

Michael Cubine
xVxT6x.jpg

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