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Guide/Tutorial: Takeoff Performance in the 777

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Jim,check your PM.


Jim Driscoll 9900k@5000,2080TI@1950
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Ok, I played around more with my hope to be able to "streamline" this on an Excel spreadsheet.  I think it is doable.  I am able to perform all the needed calculations or table lookups for Vspeeds (including wind/slope correction), full rated takeoff thrust adjustment/equivalents for TO1 and runway length adjustment (wind only since I only have the tables in this post).  The final hurdle I have is to figure out how to combine the adjusted runway length lookup (easy) with the adjusted takeoff weight (less easy, it's a non-linear, non-contiguous lookup variable) to find the assumed OAT.  It looks like Excel has the functions to do this, but I need to investigate a bit.

 

The advantage of this would be 1) not having to convert units (lbs to kgs), 2) not having to do any of the rounding (although that's not hard), 3) no math to find headwind component, 4) no need to look at a series of several tables.

 

The intent I have is to enter 1) units (imperial, metric), 2) Runway condition (wet, dry) 3) TO, TO1 or TO2, 4) Takeoff weight, 5) Runway and runway length, 6) Wind speed and direction.  You'd then get the assumed OAT and corrected V1, V2 and VR in return.  Certainly no TOPCAT, but perhaps at least a reasonable facsimile to hold us over.

 

So the issue now...

 

Does anyone have these charts for the -200LR instead of the 300ER these are for?


Eric Szczesniak

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There's a freeware tool called Utopia in the AVSIM library which does derated data. It includes a tool where you can perform a series of takeoffs at different weights and it will record the runway length used. After enough data has been collected, it will use the data to work out likely values for the exact weight entered. It already includes a

There's a freeware tool called Utopia in the AVSIM library which does derated data. It includes a tool where you can perform a series of takeoffs at different weights and it will record the runway length used. After enough data has been collected, it will use the data to work out likely values for the exact weight entered. It already includes a profile for the CS 777.


Phil Brown

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There's a lot of confusion on this in the PFPX forums, so to clarify.  OFP's do not include takeoff Vspeeds and derated takeoff data.  If included, the only takeoff performance data is in relation to maximum takeoff rate for the runway in use for current meteorlogic conditions.  PFPX simulates this in the OFP.  No Vspeeds or derate are included.  This function is all done without "opening" TOPCAT.  However, after the OFP is generated, PFPX can send the payload/fuel data from the OFP to TOPCAT (which is actually opened at this point) and you can then make your loadsheet and takeoff/landing report as you normally would.

You are able to get V-Speeds on the released OFP, hence why in the flight planning template there is a whole section on take-off performance. Numerous commands include;

 

<&TO_V1>

<&TO_Thrust>

 

etc etc.

 

 

There's a freeware tool called Utopia in the AVSIM library which does derated data. It includes a tool where you can perform a series of takeoffs at different weights and it will record the runway length used. After enough data has been collected, it will use the data to work out likely values for the exact weight entered. It already includes a profile for the CS 777.

 

Just had a look at this. Using the included PSS 777 profile, it calculates a de-rate but no assumed temperature. Most airlines use the ATM (Assumed Temperature Method), so right now this program is unfortunately no use to me.

 


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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Just had a look at this. Using the included PSS 777 profile, it calculates a de-rate but no assumed temperature. Most airlines use the ATM (Assumed Temperature Method), so right now this program is unfortunately no use to me.

 

Just had a quick test of it, and if the weights are low, you do get assumend temps. Although I had to set the TOW to 280000kg before the derate reduced below max power. Seems it preferes to change flap and static derate (TO1, TO2) before starting to use assumed temps.

 

You can also change the aircrafts profile to specify what the minimum and maximum assumed temps should be.

 

Untitled.png


Phil Brown

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Just had a quick test of it, and if the weights are low, you do get assumend temps. Although I had to set the TOW to 280000kg before the derate reduced below max power. Seems it preferes to change flap and static derate (TO1, TO2) before starting to use assumed temps.

 

You can also change the aircrafts profile to specify what the minimum and maximum assumed temps should be.

 

Untitled.png

Ok, yes, I was just able to obtain an assumed temp.

 

I might play around more with the program and profiles and see what I can come up with.


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
blueaerosofta320extbeta.png

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The airline I work for does not use TO1 or TO2 or CLB1 or CLB 2.

The laptop calculates (amoungst other things) the assumed temp for take off and Vspeeds and those are entered in the FMC by the crew.

 

Couple of questions here (and some additional interesting info).

 

1) Does anyone know which airlines use TO1/TO2 and CLB1/CLB2?

They are fixed derates.

I think (think cause I have never used them) that they just reduce by a fixed percentage.

Maybe something like TO1 reduces by 10% and TO2 by 20%?

And then you would need some means (laptop performance software)to check you can actually take off with that setting.

Maybe someone can confirm this?!

 

You can also combine fixed derate with assumed temperature, but I have no experience with this either.

 

2) What is the advantage of using fixed derates versus assumed temp method?

Cheaper performance software maybe?

 

I was just going thru the FCTM (flight crew training manual) and I can tell you a disadvantage of using fixed derates that I thought is quite interesting (yes, I had to look that up :-) )

 

P.s. maybe the below info is not true for every airline as many books like FCTM are company tailed

 

When conducting a fixed derate takeoff or a takeoff with a combination of assumed temperature method and fixed derate, takeoff speeds consider Vmcg and Vmca only at the fixed derate level of thrust. (Vmcg and Vmca are minimum control speeds below which the rudder is not effective enough to compensate for assymetric thrust)

If you have an engine failure during takeoff, and increase thrust on the other engine beyond the fixed derate limit, this could result in loss of directional control.

 

When using assumed temp method, the takeoff thrust setting is not considered a takeoff operating limit since minimum control speeds (Vmcg and Vmca) are based on the full rated takeoff thrust. At any time during takeoff, thrust levers can be advanced to the full rated takeoff thrust if required.

 

 

3) If only the assumed temp method is used by most airlines, then you guys creating (very much appriciated) T.O. tables could leave TO1/TO2 and CLB1/CLB2 out of it.

Maybe this makes things easier?


Rob Robson

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You answered your own question. Most simple way to look at it is a derate is like bolting on less powerful engines, TO1 or TO2 is TOGA thrust on those new less powerful engines that you have selected, therefore you are Vmcg/Vmca limited.

 

You cannot cancel the derate since that would be like magically bolting on more powerful engines, your Vspeeds would be invalid and you would likely lose control in an engine failure scenario

 

An assumed temp is just reducing the available power to take off, you still have TOGA thrust available and are allowed to cancel the assumed temp and go TOGA if needed.


Rob Prest

 

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You answered your own question. Most simple way to look at it is a derate is like bolting on less powerful engines, TO1 or TO2 is TOGA thrust on those new less powerful engines that you have selected, therefore you are Vmcg/Vmca limited. You cannot cancel the derate

 

An assumed temp is just reducing the available power to take off, you still have TOGA thrust available and are allowed to cancel the assumed temp and go TOGA if needed.

Are we talking about factory de-rates here or a de-rate entered through the FMC?

 

Obviously there is the GE90-110 and GE90-115 which are both the exact same engine but one is factory de-rated to 110,000lbs. However, you can still de-rate each of them through the FMC, and these can obviously be cancelled and are used when deemed neccesary by the performance manuals/software.


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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Well of course you can override and cancel but you are Vmca limited and will very likely lose control if an engine quits. If you have planned for TO1 or TO2 then your Vspeeds should have already provided a safety margin for any failures.

 

Once again, if you select TO1 or TO2 your performance data is based on those selections being max available thrust.


Rob Prest

 

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Well of course you can override and cancel but you are Vmca limited and will very likely lose control if an engine quits. If you have planned for TO1 or TO2 then your Vspeeds should have already provided a safety margin for any failures.

 

Once again, if you select TO1 or TO2 your performance data is based on those selections being max available thrust.

Sorry, misread your original post. Thought you meant you can't cancel a de-rate, period (as in it was a permanent fixture like a factory de-rate).

 

It is also possible to cancel any derate thrust limits by pushing the TO/GA switch a second time.


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
blueaerosofta320extbeta.png

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Yep, thought it must have been a misunderstanding.

 

Cheers


Rob Prest

 

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You answered your own question. Most simple way to look at it is a derate is like bolting on less powerful engines, TO1 or TO2 is TOGA thrust on those new less powerful engines that you have selected, therefore you are Vmcg/Vmca limited.

You cannot cancel the derate since that would be like magically bolting on more powerful engines, your Vspeeds would be invalid and you would likely lose control in an engine failure scenario

An assumed temp is just reducing the available power to take off, you still have TOGA thrust available and are allowed to cancel the assumed temp and go TOGA if needed.

Ok, but I guess you (the pilot) use a software progam to calculate if you can do a TO1 or TO2 takeoff and on top of that you can calculate and add an Assumed Temp.

Why?

Why not just calculate Assumed Temp, forget about TO1 and TO2 and be done with it?

 

Edit: by the way, I had 3 question. Not sure which one was answered.


Rob Robson

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It is all down to the company you fly for, the engines on the aircraft may not necessarily be owned by the airline, contracts may state state that a derate needs to be used whenever perfomance allows it, Maintenance costs are high, a whole bunch of reasons that men in suits get paid to sweat over.


Rob Prest

 

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Ok, but basically we dont know:

 

1) if most airlines use Assumed Temperature or TO1/TO2 or a combination of both.

 

2) what the advantage of one method over the other is (we only know the disadvantage of fixed derate when you add full thrust after an engine failure. What we dont know, is why one would even use TO1 or TO2?)

 

3) how much (percentage?) thrust reduction you get if you select TO1 or TO2?


Rob Robson

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