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Michael Moe

TAKEOFF REF 1/2

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Hi ,

 

I always use PFPX calculating the derates but what is it that RWY REMAIN is for ? I can put in a value for instance 008 (00800 feet) but does it change anything ? (offcause it does :-))

 

 

Thanks

Michael 

 

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If you use GPS position update, it'll make no changes. If not - FMC gets updated coordinates on TOGA press.

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I always use PFPX calculating the derates

You can't use PFPX to calculate derates and assumed temperature. Did you mean TOPCAT?

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You can't use PFPX to calculate derates and assumed temperature. Did you mean TOPCAT?

Yes offcause sorry but via PFPX

 

Michael

If you use GPS position update, it'll make no changes. If not - FMC gets updated coordinates on TOGA press.

Not sure i understand. What is it for? Derates?

Thanks Michael

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Not sure i understand. What is it for? Derates?

Thanks Michael

Nothing to do with aircraft performance, just more accurate coordinates for nav performance.

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Not sure i understand. What is it for? Derates?

 

Rostyslav might have to correct me on this, but as he said, it's about more accurate positions for departure.

 

Remember that your IRU position will drift over time. The only reason it remains highly accurate over time is through periodic updates by DME and/or GPS. It can also be fed a more accurate position by correlation. What this means is the database has a known position for the beginning of the runway in coordinate form. When you hit TO/GA, this position is used to update the IRS position to ensure that its position is accurate prior to the aircraft leaving the ground. If the runway is being shortened (from where you'd begin the takeoff roll), then you wouldn't want the FMS to grab the position at the beginning of the runway. You avoid this by telling it how far the runway has been shortened, which allows it to pull a position offset from the origin position for the update (or it inhibits the runway position update entirely - I'm not sure on this part).

 

Probably more than you wanted to know, but hey...

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