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Guest AndyH8

Wet n Dry

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Guest AndyH8

Hi NG guys.Does the FMC model wet runways?Was flicking through to set a wet departure runway and couldn't see an option for this in the parameters.Also I do see descent paths being unachieveable quite often and also drag required so hence deploying spoilers and using speed on MCP. Is this realistic. Saw a few posts re the vnav pth being rather difficult to achieve in real life and hence the above method being used.CheersAndyEGNX

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Guest AndyH8

OkFound that Fs9 don't allow for wet runways in an answer by Randy. But can't the FMC compute this to add realism. Or is the FMC 'tied' to Fs9 in some way to prevent this.Also still puzzled about orig question 2.CheersAndyEGNX

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Andy,>Does the FMC model wet runways?No and neither do FS.>Also I do see descent paths being unachieveable quite often and also drag required.Yes. This has been pretty well covered in this forum. PATH UNACHIEAVABLE is most likely due to a too steep dive angle. DRAG REQUIRED is due to the plane catching up on speed while trying to keep the path. I could imagine the latter message being an indication of the former to come if the crew doesn't rectify the speed issue.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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| Asus Z270-A | Intel i5-7600K @ 4.8 GHz OC/H2O | nVidia Geforce GTX 1070 8GB OC/O2|

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Guest Soulman

With regard to unachievable descent paths, make sure you enter the forecast winds for your descent on the DES page under FORECASTS (if you haven't already done so).Also, if you are entering in restrictions (i.e cross waypoint XXXXX @ FL120), make sure the aircraft has an adequate distance to acheive the decent. A rule of thumb is 1000ft for every 3 nautical miles. This comes from the more standard practice of using your cruise FL to make an estimate of the distance needed to descend. Imagine you are at FL380, to attain the distance required you drop the zero, multipy by 3 and add 10. So, from FL380: 38 x 3 = 114 + 10 = 124nm. You must remember this is only an estimate and does not take into account wind allowance and other factors such as crossing or speed restrictions.I usually give around 2500ft for every 3 miles just to ensure a more gentle transition.Another option would be to increase your speed on DES. Instead of using 260kts, I use 300kts. This way you have less chance of overspeeding on descent.

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>Ok>Found that Fs9 don't allow for wet runways in an answer by>Randy. But can't the FMC compute this to add realism. Or is>the FMC 'tied' to Fs9 in some way to prevent this.>>Also still puzzled about orig question 2.>>Cheers>>Andy>EGNX Well yes it could be made that way but since MSFS does not have performace effects from rwys it really does not matter and would cause you to have incorrect thrust. Trust you me, VNAV is pretty darn good and to answer your question it certainly does do those vary things in rl..[h4]Randy J. Smith[/h4]


Randy J Smith

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Guest AndyH8

OK Guys I'll Try your suggestions.If I allow T/D as computed I may well have to increase speed in the descent page to get down ok. However if I decide on an earlier descent to achieve the contraints, I would use Descend Now, right?Thanks again.AndyEGNX

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Andy,DES NOW will not make you achieve any contraints. This will only start a shallow 1000 fpm decent and will follow the path once it catches up with it. See it as a "gentle transition" from CRZ to DES instead. Also handy when ATC tells you to decend early.You should do some research on VNAV PATH here on the forum. There's an abundance of information about it.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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| Asus Z270-A | Intel i5-7600K @ 4.8 GHz OC/H2O | nVidia Geforce GTX 1070 8GB OC/O2|

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>>Ok>>Found that Fs9 don't allow for wet runways in an answer by>>Randy. But can't the FMC compute this to add realism. Or is>>the FMC 'tied' to Fs9 in some way to prevent this.>>>>Also still puzzled about orig question 2.>>>>Cheers>>>>Andy>>EGNX>> Well yes it could be made that way but since MSFS does not>have performace effects from rwys it really does not matter>and would cause you to have incorrect thrust. >It doesn't have any affect on thrust. You would just have a lower V1 that allows you to stop within the flight manual's accelerate-stop distance for an RTO considering the lower braking friction on the wet runway. Using this V1, you would also only be at 15 feet at the end of the takeoff distance if you continued the takeoff after an engine failure occuring just before V1 is reached. The allowable takeoff weight may also need to be reduced.Don S.

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