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Driver170

Takeoff Speeds

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In the FCTM it mentions in the Takeoff speed section -

 

The FCOM and FMC computed takeoff speeds (if enabled) are only valid for dispatch performance based on balanced field length, improved climb, the most forward CG limit, and dry or wet runway.

 

This is where i'm confused, so why in the FCOM dispatch part you don't have the V speeds unlike the PI?


Vernon Howells

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This is where i'm confused, so why in the FCOM dispatch part you don't have the V speeds unlike the PI?

 

I guess that it because the document you are supposed to use for all calculation is the FPPM (Flight Planning and Performance Manual), not the FCOM.

 

In the FPPM, you have all the tables and curves required to calculate the takeoff speeds, thrusts, and so on...


Romain Roux

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Avec l'avion, nous avons inventé la ligne droite.

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I don't have the anwser to your question but following the definition you gave on your first post, I would guess so.

But you will surely have a more accurate answer from others persons around there.


Romain Roux

204800.pngACH1179.jpg

 

Avec l'avion, nous avons inventé la ligne droite.

St Exupéry, Terre des hommes.

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But you also have this

 

The FCOM and FMC computed takeoff speeds are not valid for dispatch performance based on optimized V1 (unbalanced field length), Improved Climb, alternate forward CG limit, or contaminated or slippery runway.

 

But in the PI you can calculate your V SPEEDS?


Vernon Howells

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What do you call PI? Sorry, I'm not always familiar with the acronym?


Romain Roux

204800.pngACH1179.jpg

 

Avec l'avion, nous avons inventé la ligne droite.

St Exupéry, Terre des hommes.

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I'm not home so I don't have access to the my sim computer and terefore to the FCOM, but as far as I remember, the values given in the FCOM are for only one flaps config.

With the FPPM, you can calculate your takeoff speeds for all the takeoff flaps configs and thrust configs.


Romain Roux

204800.pngACH1179.jpg

 

Avec l'avion, nous avons inventé la ligne droite.

St Exupéry, Terre des hommes.

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@Driver170 I'm not sure where you going with this or why you want to dig up V speeds in the FCOM or calculate your own V speeds from the performance manual.

 

Just look at the V speeds in the FMS after you've loaded your flight plan into it and use those values. Done. Finished.

 

I can tell you in the real world the pilots do not do what you are trying to do...so I don't know why you are expending valuable time and energy that you could be using to go fly!!! Just read the V speeds from the CDU and go!!!


Ralph Freshour -- PMDG 737NGX | CS 777

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Vernon,

 

If you read the text that goes with the PD and PI chapters in the FCOM it explains their purpose. The Performance Dispatch is intended to enable a crew to self dispatch if there is no dispatch department to do it for them. As Romain said, it's only provided for Flap 5. The PI chapter is a supplement to the FMC performance calculations and includes V speed adjustments for slippery runways, for example. It can also be used in flight in the event of an FMC failure. As it's related to the FMC calculations I assume this is all balanced field data for takeoff. Unbalanced field is a much more complex subject. However I am not a pilot and I have no background in this and so stand ready to be corrected about this.

 

If you think about it, since the V speed data is presented in the PI chapter there would be no point in repeating it in the PD chapter. I'm not sure why you expect it to be in there. The PD basically gives you data to show your flight can be dispatched within legal limits. Not too heavy for the runway, sufficient fuel on board, etc.

 

As Ralph said, probably best not to overthink this. PMDG haven't supplied the data necessary to do the calculations you appear to be envisaging.


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@Driver170 I'm not sure where you going with this or why you want to dig up V speeds in the FCOM or calculate your own V speeds from the performance manual.

 

Just look at the V speeds in the FMS after you've loaded your flight plan into it and use those values. Done. Finished.

 

I can tell you in the real world the pilots do not do what you are trying to do...so I don't know why you are expending valuable time and energy that you could be using to go fly!!! Just read the V speeds from the CDU and go!!!

 

Hi Ralph, i'm not calculating any Vspeeds! I was reading the FCTM takeoff speeds part and just got a bit mixed up with what it mean't.

If you read the text that goes with the PD and PI chapters in the FCOM it explains their purpose. The Performance Dispatch is intended to enable a crew to self dispatch if there is no dispatch department to do it for them. As Romain said, it's only provided for Flap 5. The PI chapter is a supplement to the FMC performance calculations and includes V speed adjustments for slippery runways, for example. It can also be used in flight in the event of an FMC failure. As it's related to the FMC calculations I assume this is all balanced field data for takeoff. Unbalanced field is a much more complex subject. However I am not a pilot and I have no background in this and so stand ready to be corrected about this.

 

If you think about it, since the V speed data is presented in the PI chapter there would be no point in repeating it in the PD chapter. I'm not sure why you expect it to be in there. The PD basically gives you data to show your flight can be dispatched within legal limits. Not too heavy for the runway, sufficient fuel on board, etc.

 

Good stuff Kevin. I'm not wanting to calculate any Vspeeds, like i said i was reading the FCTM and was getting mixed up with some parts with what it mean't.

 

It mentions this -

 

The FCOM and FMC computed takeoff speeds (if enabled) are only valid for dispatch performance based on balanced field length, improved climb, the most forward CG limit, and dry or wet runway.

 

So it says only valid for Dispatch? so when does performance inflight start? In the air? Or once the pilots start Preflight? Because you do the FMC during preflight and that would mean InFlight?


Vernon Howells

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The Text section of performance inflight says:

 

The speeds presented in the Takeoff Speeds table as well as FMC

computed takeoff speeds can be used for all performance conditions
provided that adjustments are made to V1 for clearway, stopway, anti-skid
inoperative, thrust reversers inoperative, improved climb, contaminated
runway situations or brake energy limits. These speeds may be used for
weights less than or equal to the performance limited weight.

 

Not sure if this clears some confusion for you.


David Chen

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That makes sense! But why mention using takeoff speeds in the dispatch when there isn't any vspeeds but only in the PI ?


Vernon Howells

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Hi Ralph, i'm not calculating any Vspeeds! I was reading the FCTM takeoff speeds part and just got a bit mixed up with what it mean't.

 

Good stuff Kevin. I'm not wanting to calculate any Vspeeds, like i said i was reading the FCTM and was getting mixed up with some parts with what it mean't.

 

It mentions this -

 

The FCOM and FMC computed takeoff speeds (if enabled) are only valid for dispatch performance based on balanced field length, improved climb, the most forward CG limit, and dry or wet runway.

 

So it says only valid for Dispatch? so when does performance inflight start? In the air? Or once the pilots start Preflight? Because you do the FMC during preflight and that would mean InFlight?

It was when you talked about unbalanced field I thought you might be calculating V speeds. I think the FCTM is merely repeating the limitation that the FMC V speeds are for those conditions. It doesn't imply the PD section allows you to calculate them.

 

If those conditions do not apply, e.g. slippery runway, then FMC V speeds should be adjusted. Also dispatch might have provided adjusted speeds to use instead of the balanced field numbers. Typically to maximise TOW. At least that's what I've read. A pilot would give you a complete answer. Though even pilots disagree on the details.


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So the FMC speeds are basically from the FCOM?

 

I believe PMDG states in the documentation that the FMC Vspeads are calculated using formulas based on the FPPM but that Boeing would not allow the FPPM to be distributed with the product.

 

Dave


Dave Paige

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