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Guest hellogoodbye

Weather and stuff like that...

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I'm confused when it comes to weather and stuff like that... I know I can enter the wind (direction and strength) in de 737NF FMC, but where do I get that information from...? And should I enter the direction just as it is or as it is coming against my airplane? And what about all those barometer things (QNH), transition level and altitude, winds, crosswinds, tailwinds, pressure, whatever...Anyone knows a site where I can learn all I need to know about the weather and all that stuff that is OUTSIDE of my airplane? I can fly without knowing it, but it just does't feel right...Jeroen van Engelen

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Hi,something you could learn from the AS2004 instruction manual that's free on the www.hifisim.com site.Other things could be learned buying a good aviation weather book or browsing thru the net.Anyway, just get these infos that are really important for your flying:QNH = is the setting of your altimeter to the local pressure (reduced to sea level). Setting to QNH (the "B" button in FS) will make your altimeter read the field elevation when on the ground. All instruments procedures are referred (if no differently stated) to altitudes in QNH. You'll need to have your altimeter set with the local QNH (got from ATIS, AWOS, Tower, Approach or Center)when you are departing and up to the transition altitude (18000 ft in the US, variable in the other countries, in Italy for example around 6000 ft) and when approaching to land when below the transition level (FL180 in the US, in Italy usually around FL70 or 80). The word "transition" means the transition from a QNH setting to a standard (29.92 inHg or 1013.25 hPa or 760 mmHg) setting (named QNE) or the viceversa.You'll fly "altitudes" when on QNH, flight levels when on QNE and "heights" when on QFE (another altimeter setting that will make your altimeter read zero on the ground). The radio altimter will give your actual distance from the terrain (usually only below 2500 ft).Crosswind = that component of the wind that flows perpendicular to your flight path (makes you drifting)Tailwind = that component of the wind that flows parallel to your flight path blowing from the tail to the nose (increases your groundspeed but decreases your airspeed)Headwind = that component of the wind that flows parallel to your flight path, but blowing from the nose to the tail (increases your airspeed but decreases your groundspeed) .Hope this helps you !

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A lot depends on how you generate weather Jeroen, I suspect you are using the default FS weather which you can set yourself.I don't use the default weather but at a guess I would say you can find out most things you want from the weather 'pages' in FS where you set the weather.I know you can set barometric pressure (QNH), surface winds, & temperature so you an read those values. You can also set higher alititude winds so again you can read those values.To be honest if you are interested in flying in different weather conditions I would suggest buying ActiveSky 2004 http://www.hifisim.com/, IMHO the best add-on weather program around, it also has descriptions of how weather reports are generated to help you understand better.For the entries into the FMC ActiveSky gives you winds and temperature at different altitudes so all the entries you need are there.Wind values are entered 'as is', no need to calculate the cross wind component, the FMC does that.Transition altitude and level are bounderies of vertical airspace where your altimeter changes the way it reads your altitude.Above the transition level all aircraft set their altimeter to a standard pressue of 29.92 inches or 1013 hpa, this is so ACT can keep the virtical speration constant.Below the TL your altimeter is set to the local pressure (QNH) so you don't run into high ground.Normal method is to change from QNH to standard when climbing through the transition altitude and swap back from standard to QNH when descending through the transition level.Hope that helps.

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Thanks Enrico and Vulcan, that cleared up some things (and I'm not talking about the sky here! ;))So in the FMC I only have to enter the winddirection and strenth (like 240/8) and the FMC will take care of the rest?And is there a specific difference between Transition LEVEL and Transition ALTITUDE...?Jeroen van Engelen

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>Thanks Enrico and Vulcan, that cleared up some things (and>I'm not talking about the sky here! ;))>>So in the FMC I only have to enter the winddirection and>strenth (like 240/8) and the FMC will take care of the rest?Correct>And is there a specific difference between Transition LEVEL>and Transition ALTITUDE...?Not sure what you mean by specific difference Jeroen?The transititon level is a fixed altitude for a given location (as explained by Enrico) but the transition level can vary for that location based on the current barometric pressure (QNH).IIRC the aim is to have the TL and TA seperated by about 1,000ft, someone correct me if I'm wrong.TA's & TL's for Europe are usually given on SID & STAR charts for specific airports because there is not standard value as there is in the USA.As I don't use the built in ATC I'm not sure how this affects that ATC, I suspect FS sticks to a standard USA value of 18,000ft.However if flying on line with VATSIM or the other networks you need to know the TL & TA values especially if there is no ATC.If you are under the control of a human ATC things are a little easier.If you are departing an airport you will normally be given an initial altitude (therefore you are on QNH - this is ALWAYS set when at an airport). Later on you will get the instruction "Climb to flight level xxx" (say 180) Because the instruction was to climb to a flight level you know you will be passing through the TL so you can set your altimeter to the standard pressure of 29.92 inches or 1013hpa.When arriving at an airport ATC will say "Descend now to xxxxft, QNH is xxxxhpa". Because the instruction is given in feet and not flight levels you know you are descending through the TL so would set your altimeter to the local pressure (QNH). Note also that ATC must give you the current QNH.When on the ground with QNH set correctly your altimeter will not read zero feet but will show the height of the airport above sea level.Any wiser :-)>Jeroen van Engelen

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We are getting close! :)Your remarks about ATC calling out feet and levels clears up a lot. I only got ONE small question though, because the main question about the 'specific difference between TA and TL' is still unanswered, UNLESS you made a little mistake in the following sentence...:"The transititon level is a fixed altitude for a given location (as explained by Enrico) but the transition level can vary for that location based on the current barometric pressure (QNH)."If this should have been this..."The transititon altitude is a fixed altitude for a given location (as explained by Enrico) but the transition level can vary for that location based on the current barometric pressure (QNH)."...then everything would be really clear! :)So, did you make a typo or do I still not get it? ;)

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Yes. it is so:the transition altitude is the FIXED altitude (for each location, normally printed on the charts) crossing which CLIMBING you change your altimeter from QNH setting to QNE (standard) setting.So, to make thing easier:the TA is crossed UPWARDSthe TL is crossed DOWNWARDS.They are usually about the same or separated by about 1000ft (albeit not always so. Example: at Turin the TA is always 6000ft QNH, the TL is FL70 if QNH is above 1013 hPa, FL75 if below 1013 and above 990, FL80 if below 990).Hope this helps clarify you.

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Sorry Jeroen, that was a typo :-doh TA is fixed, TL can vary.Quote from an approach chart for Athens"Transition Level by ATCTransition altitude 9,000ft"A search of the Web for 'Transition level' should turn up sites that will give you a more authoritive expalanation.

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