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Bman2006

RNAV and Derate Questions

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Hey all-

 

1) I don't do a whole lot of RNAV approaches. At what point do you turn off the VNAV? I guess the question is - are the crossing altitudes really for reference only or can you actually use the VNAV guidance for approach or are they LPV type approaches where you have both lateral and vertical guidance?

 

2) I have been using topcat for pre-planning (and FSBuild). Question - what is the difference between the TO information listed at the top and the 'reduced' thrust? It appears to me that that the thrust is still set to an assumed OAT of +34c and D-TO in both of the circles areas..yet, the v-speeds are different. Don't get me wrong, they are very close. I am just trying to understand exactly the difference between my selected derating and the information provided under "reduced".

 

 

 

fsx2011-000.jpg


Benjamin Van Eps

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1) I don't do a whole lot of RNAV approaches. At what point do you turn off the VNAV? I guess the question is - are the crossing altitudes really for reference only or can you actually use the VNAV guidance for approach or are they LPV type approaches where you have both lateral and vertical guidance?

 

On RNAV approaches you can use LNAV/VNAV or IAN. You can also fly LNAV/ V/S from FAF, but in many airports it will have higher MDA because it's less precicion.

 

 

 

I'm not turning them off. Sometimes I use autopilot to DA, then I can fly visually or use F/D gudance for advisory. Sometimes in VFR I turn off CMD, A/T, cycle F/Ds off then on and fly visually.

My general advise would be to use LNAV/VNAV at least to FAF to get into every constraint correctly.

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Hi!

Regarding question number two I think the difference is that the D-TO field has calculated on the weights you enterd (151181) and thus gives ju speeds 142-142-142. The reduced table is giving you the speeds for the MTOW for that reduced thrust. In the table for 34 degrees the MTOW is 152042 and that's why the speeds is a bit different. A question though, why are you taking of with flaps 25?


Regards

Stefan Hillblom

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Thanks guys -

 

Roysyslav - so, just do I understand RNAV = LNAV/VNAV for all RNAV approaches? How is an RNAV approach different from say a GPS LPV approach? Would they be one in the same?

 

Stefan - Gotacha. That makes sense. What would this be needed for? Last minute adjustments to the PAX/Cargo/Fuel?

Flaps were given to my by TopCat on a relatively short field. At 5 and 10 flaps, assumed / flex derate is not authorized. At 15 there was one temp of 30 but margin was tiny. At 25 flaps, I could reduce to 34+c and still have some runway remaining.


Benjamin Van Eps

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Ahh okay. Must try out that field. :)

guess your correct with the last minute change to pax/cargo/fuel. And also you see on the bottom of the table what the difference in wind do to your MTOW for the reduced thrust. So you can quickly add or subtract weight to get a new reduced thrust temperature.

That is my guess anyhow.


Regards

Stefan Hillblom

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