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Richard McDonald Woods

En route winds: plan v actual

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I have started a new topic because I wish to differentiate this thread from the existing threads dealing with importing AS2012 winds. Other threads have assumed that actual en-route winds can be used prematurely for pre-flight planning.

 

I believe that we should be separating the processes of planning for route winds and handling the actual winds encountered.

 

In programming the FMC during pre-flight, we should be using the flight planning process en route winds to populate the flight plan waypoints. This means using, in my case, the PFPX wind forecasts from the OFP, which are shown(?) in tab-delineated format.

 

Separately, I may wish to modify the en route winds during flight so that I can plan for en route FL changes and revise my ETA and fuel usages. These updates I would hope to source from AS2012.

 

Without separation of planning and actual processes, I would never encounter the situation of having to divert because of fuel shortages caused by changes to winds encountered during flight.

 

This leaves me with three questions:

 

- can I use the en route winds forecast from the PFPX OFP to create my .wx file in PMDG/WX (i.e. is it truly in tab-delineated format so that I can copy it to PMDG/WX via NotePad without further editing)?

 

- can PFPX be asked to create a .wx file in PMDG/WX to the same rules as other vendors are being asked to do?

 

- can the PMDG777X be programmed so that any .wx file that has the first eight characters of the origin and destination airfields be used, and can that be selected from a list of those matching airfield pairs displayed on the FMC?

 

Cheers, Richard

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Discrepancy between reported winds aloft and actual winds aloft is actually part of life, and proper fuel planning takes it into consideration. I still don't have PFPX, but I'm guessing your fuel calculation's aren't correct because a difference in winds shouldn't be steep enough to cause a divertion under normal circumstances. How long are your flights?

There are many legal criteria for planning fuel (Through PET, Through PSR, Redispatch...), but you should use the standard one.

 

RAMP FUEL = TAXI + TRIP + (ALT + CONT +  HOLD + EXTRA)

for flight planning, the sum of ALT+CONT+HOLD+EXTRA is considered RESERVE FUEL, and it is the RESERVE amount that you should put in the box during CDU PREFLIGHT.

 

TAXI FUEL:

Is the fuel required for APU operation for conditioning and engine start and also the fuel necessatry to bring the airplane to the runway. TAXI fuel isn't part of the take off fuel, so it is not included in the ATOM (actual take off mass) figures.

 

TRIP FUEL:

It's the fuel required for take off at the origin, fuel to cover the air distance (not the ground distance) from TOC to TOD at the planned FL and the planned STEP CLIMBS, descent to the IAF along a STAR and the fixed landing fuel quantity. Curiously, fuel required to taxi to the gate is not included here.

 

ALTERNATIVE:

Includes full missed approach procedure at the destination, a climb to cruise altitude and cruise to alternative destination including descent, approach and a fixed landing quantity.

 

CONTINGENCY:

Is the fuel loaded to prevent what is happening to you. It's usually 5% of TRIP FUEL. Its purpose is to compensate for fuel consumption deviations, headwinds greater than planned, impossibility to fly at the recommended flight level, ATC route changes.

Some operators are authorized to use 3% of TRIP when they have ERA (enroute alternative) at a distance from flight path not greater than 20% total distance, if I remember correctly.

 

HOLD FUEL:

Also called Final Reserve. It is the fuel required to hold at 1500ft AGL over the alternative at the recommended speed for 30 minutes. That is a lot of JET-A1!

 

EXTRA:

This one's captain's discretion. I remember back when I was working in Air Europa as cabin crew, on the GCLP to LEMD flight on the 737, that ramp fuel was usually around 9600Kg. I remember Captains almost always rounding that to 10000Kg. The reason for this "extra" amount is to compensate for opreation in busier than normal airports among other things that don't directly affect standard fuel planning. Let's call it "non ryanair fuel"...


So, check your numbers and make sure that PFPX is calculating fuel correctly.

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Hi Omar,

 

I haven't said that my fuel planning calculations are incorrect at all. Please re-read my post carefully. I am ONLY trying to differentiate between plans and actuals.

 

Surely you can't deny that winds may change between the time of planning and the time of crossing? If you are not interested in the changes caused by the passage of time, then I suggest that you will not be one of those wishing to upload new winds en route. But I may.

 

R :Thinking:

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Sorry. I just re-read your post. I see what you are trying to do. You are trying to simulate a differentiation between Take Off Datalink (PFPX) from In-Flight Company Datalink (AS2012).

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