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PFPX Weight Estimates vs Actual

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As discussed Here, there is an easy way to have a precise match between a PFPX OFP and the actual wight of the aircraft. This is helpful in planning, but is this the most realistic way to plan flights?

 

In real life, a pilot would get a final closeout with weight and performance data via a fight attendant or ACARS right before push back or during taxi. This would be an amendment of the weights that are provided in the OFP. Many factors such as more or less passengers, cargo, and fuel can change from the time that the flight plan was printed to the time of push back. Also provided in a closeout would be runway specific performance information for takeoff, and V-Speeds. Taking the updated weights from the closeout, a pilot could apply the corrections for cruise fuel usage provided in the OFP.

(Ex: TRIP CORR FOR 2000 LB TOW INCR: +123 LB / 2000 LB TOW DECR: -125 LB)

 

In the sim, one could plan a flight in PFPX using the standard wights and have the estimated load in the OFP. Once in the sim and ready for push-back or taxi, you could get your final takeoff weights, and calculate v-speeds if done externally, as well as any other performance related calculations, just as a real flight crew would do with a takeoff closeout.

 

I am not 100% competent in this subject and others may have more information on this topic. How do most people plan their weights in PFPX or other flight planning programs. Could this be a more realistic way to flight planning instead of putting in exact weights to into PFPX, or does it cause too much hassle?

 

Thoughts or suggestions on methods of planning weights would be appreciated.

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Could this be a more realistic way to flight planning instead of putting in exact weights to into PFPX, or does it cause too much hassle?

 

Very good question Jacob.

 

A lot of the simmers tend to get overly hyped up about the numbers game.  It's really a game of imprecise precision.  If you think about it, the planned loads are coming from the reservation system, based on assumed passenger weights.  From there, as you mention, you get final counts from the FAs, or perhaps the final number checked in via some other automated system.

 

From there, you have a difference in the planned weight from booking, and the planned weight on the actual passenger counts.

 

Even then, though, those weights are off what the plane actually weighs because the number of passengers is multiplied by a passenger average weight (varies by operator, though the FAA has its recommendations as a standard).  So, not only do you have a discrepancy between booked/planned and confirmed/planned; you also have a discrepancy between the averaged weight and the actual weight.

 

Because there's all that error added in there, I don't get too concerned about matching everything up, precisely, like a lot of the sim group does.  Additionally, unless you have a program that randomizes attrition rates for your passengers, I wouldn't worry too much about the initial number versus the flight attendant final count numbers (just assume what you get in PFPX/TOPCAT is what the FAs passed up as final numbers).  Sim passengers seemingly manage their calendars a lot better, and don't have to deal with the TSA.

 

So, unless you get a program to start hiding some of the actual numbers from you and then surprising you with new numbers after everyone has boarded, I wouldn't go too far down the road of trying to get into the "final numbers game" that real world pilots have to deal with.  I'd honestly go with your first question, that I'll turn into a statement: "despite there being a way to match things exactly, it's more realistic to leave some error in there to approximate the realistic situation where passengers do not weigh the same, and some attrit."

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it's more realistic to leave some error in there to approximate the realistic situation where passengers do not weigh the same

Exactly what I was thinking. When it comes to the programming the FMC, would it be realistic to enter the estimated ZFW from the OFP into the ZFC slot? I am assuming there is no way for the aircraft to know its ZFW in real life without telling it, unlike in the NGX.

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When it comes to the programming the FMC, would it be realistic to enter the estimated ZFW from the OFP into the ZFC slot?

 

Yep.  The difference in the weights could be more realistic, at least on the assumption that even the real flights are never going to get it exactly, unless we start weighing every passenger.

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It's really a game of imprecise precision

Hi Kyle,

superb definition....

You great.!

Best Regards

Andrea

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It's really a game of imprecise precision

Hi Kyle,

superb definition....

You great.!

Best Regards

Andrea

 

Thanks Andrea!

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unless we start weighing every passenger.

Kyle

 

Forget the pax and FSX for a minute. In the RW does each plane have specific empty weight based upon items that may have been added or removed since it was delivered by the manufacture. Say a 737-800 was delivered to American Airline with an empty weight of 94150 lbs 13 years ago. Since delivery the seat material and configuration has been changed thee times, an additional lavatory added, insulation has been changed to a lighter material, lighter overhead bins replaced the original bins, etc. The empty weight is now 92073 or 2077 lbs less than when it was delivered. Do you know if this new weight change is used in flight planning and also changed in the FMC?

 

Thank you

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Do you know if this new weight change is used in flight planning and also changed in the FMC?

 

Absolutely.  This goes as far down as the Cessnas and Pipers people train in.  Any equipment changes are tracked and noted, as appropriate, in the aircraft documentation, and must be factored into the related performance figures.  That's why it's not a good idea to use the generic performance and weight and balance tools available for aircraft types online (and why most of them warn you to use your aircraft's data when actually planning the flight).  As an example, I fly three 172s out of JYO routinely.  Each one of them has its own weight and balance form on my iPad as each one has different equipment installed.  If you have PFPX, note how the database is at the aircraft registration level, and not just at the aircraft type level.

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