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Transition altitude

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From a real pilot perspective, is it correct to say that when you reach the transition altitude (18,000 feet by default in FS), you must:- change the altimeter setting to the standard setting (29.92 inHg or 1013.2 hPa)- manage the speed in Mach instead of knotsIf this is wrong, please let me know when should I switch to Mach speed during the climb.Thanks !!Eric

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Eric,I'm not a r/w pilot but I do know that you must set the altimeter to the standard 29.92 (1013.2) on reaching the transition altitude. When descending through the transition level you set it back to local pressure (QNH I believe).As far as switching from IAS to Mach is concerned I'm not aware of any rule for that. Maybe someone with more knowledge can chip in?Cheers,

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Last year I flew a Piper Aerostar up to FL 250. Changed the baro to 29.92 at 18K, and there was no mach meter on board. Never have even seen one on those planes. Yes, at the higher altitudes Mach is the best method for speed measurement, but I know of no regulation concerning this, and certainly none that concerns the transition altitude and the use of Mach afterwards.Regards,http://www.dreamfleet2000.com/gfx/images/F...R_FORUM_LOU.jpg

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What exactly is 'transition altitude' as i've seem some approach charts to airports that publish a transition of 3000ft?

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Tranistion altitude is the QNH height above which you need to reference heights in FL wiith 1013 on the alty subscale.Descending you have the transition level, below which heights are to be referenced to QNH altitudes.Generally, if you intend to climb to an FL you will select 1013 as you begin the climb. Conversely you would probably select QNH as you being the descent...unless you have been asked to report an altitude/FL on the way up/down. Regardless, airways equiped aircraft have two altimiters, it is normal practice to have the 2nd one on QNH for the duration of the flight.

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I imagine this is for two reasons:1) Aerostar would unable to reach its critical mach speed at any altitude. Jets use mach meters because to ensure thay don't exceed Mcrit.2) The Aerostar will not exceed 300kts in normal flight conditions. Above 300kts TAS compressability distorts the ASI reading. compressability will tend to cause the ASI to overread. Mach meters don't suffer from compressability errors they measure the difference ratio of pitot and static pressure rather than the difference and so are self correcting for density and temprature.

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You can calculate the average height for transition to mach.Local speed of sound = 38.94 * SQRT(temp kelvin). The temp kelvin at FL150 = 258 so 38.94 * 16.1 = a local speed of sound of 626kts. If we wanted to monitor mach at about .60 then 626*.6 = 375 kts TAS = about 300kts CAS (ASI). That is about the indicated speed you might expect at FL150 (maybe more like 280kts actucally but you get the idea) so the point at which you would may want to monitor Mach would be at or before FL150 with an ISA atmosphere. FL250 seems much too high.

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In the US you wait until crossing the transition level before switching to 29.92 in. Hg. It's not done on the climb out.I don't know for certain but I believe mach numbers are only used by aircraft who have to be concerned with it. At mach 1, airliners will receive damage and even at mach 0.9 it may go mach 1 somewere on the plane were air is flowing faster than at the sensing equipment (think of the faster air flowing over the wings).----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

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If I recall there is yet another 'transition' altitude during climb-out at which pilots would switch from flying constant IAS AP-mode to constant Mach. I believe this one occurs quite high - almost at FL300 or somewhere close to it.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2

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<>Correct and I can't imagine that any country would require going to 29.92 just because a pilot INTENDS to climb above FL180. Objects with which you can collide are referenced in MSL altitude which can only be useful when the barometric pressure over a given position is correctly set on the kollsman window of the altimeter.If everyone went to 29.92 at lower altitudes, airplanes at night or in IFR would be running into a lot of things.There are few obstructions on the planet above 18k MSL and where there are, I am certain that there is PLENTY of room calculated into the MEA restrictions to keep the ships off the granite.I don't think there is any Mach speed reporting requirement...at least not in the 20s. I once kidded with a very bored controller on the way back east from Witcihta in a C340, late at night and at FL190 that I was "level at Flight Level One Niner Zero, indicating point three Mach."He actually thought that was funny.(:Jim

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the answer is yes. You go to 29.92 when you hit fl018 and switch to mach speed just after...billg

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I'd like to add that 'Pressure Altitude' is another factor (key thing to remember here is weather patterns). At lower altitudes altimeter settings are very important as 1,000ft can feel like 5,000ft on an aircraft. If you have your altimeter set wrong you could be flying at 2,000ft but you gauge says 1,500ft or vice-versa. As you get to higher altitudes the pressure is pretty standard plus there's no ground obstructions... The weather is pretty much below you as well which would affect air pressure. Air is thinner the higher you go which again makes pressure on the aircraft less a factor and more standard.

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You are right Jay! FL 270 is the general standard to switch over to Mach reading, the pitot IAS becoming unreliable above that altitude.Paddy.

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One other point to remember is that flight levels vary around the world and can be as low as 3,000ft at EHAM, 5,000ft at EGCC and 6,000ft at EGLL.FS2004's built-in ATC does not use transition altitudes and levels. If you want a more realistic experience then try Radar Contact. Click on the icon in my signature for what it can do.End of shameless plug! :-hahCheers,

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UK Lower Airspace transition level is 10000ft (not 18000ft as in the USA). So when climbing ie on a SID from EGKK you would reset your altimeter to 10.13mb on passing 10000ft. Your "altitute" then officially becomes a "Flight Level" (which lets ATC know you are operating on the standard pressure setting).

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Yes Jay,you are correct. FL 270 is the flightlevel for switching over to Mach-reading; the pitot fed IAS becoming unreliable then.Paddy.

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Wrong. Transition altitudes in the UK are between 3000 and 6000ft (why they would have different ones in different areas of the country beats me).Maybe in some mountainous areas it's 10k ft, but not in general.

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Some charts also give the Transition Level is the lowest flight level available for use above the transition altitude.

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>Yes Jay,you are correct. FL 270 is the flightlevel for>switching over to Mach-reading; the pitot fed IAS becoming>unreliable then.I think good Air-data computer can correct most errors. Piper Meridian goes to FL300 and there is no Mach meter on this aircraft and its AOM doesn't talk about IAS being unreliable above FL270.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2

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