Evening all.I've done a search, but can't find many answers that agree with each other...I'm not sure when to change from airspeed to Mach.I've been under the impression it was Mach above Transition Level, Airspeed below.But another poster seemed pretty adamant it was "about FL280-300".My problem with the TL is thus: in New Zealand, I'm advised our TL is 4000feet. This seems to be quite low to be worrying about the speed in terms of a percentage of the speed of sound!Which leads me to believe my understanding is bollocks!Anyone know for sure, as opposed to "best guess"?Thanks all.Rock on FSX!CheersTimNZWN

TA in New Zealand is 13000' with TL FL150.The transition to mach is somewhere over FL230

Hi Tim,Transition Altitude (and Level) are an altimeter setting thing. Have a search on the forums and there have been many discussions regarding this and you will find some very detailed descriptions of this subject.The altitude at which you switch from IAS to Mach is variable. It depends on many things but put simply....Preflight - decide at what IAS you want to climb at and at what Mach no. to climb at. Both these are normally available in the aircraft performance notes or readme's. If you don't have this info then as a ballpark figure - jets climb at around 300kts or mach .76 (that's a real rough guide guys).During the climb - climb at your IAS until your mach number equals the climb mach no you are looking for. Then climb at that mach no.During the descent - the opposite is true, descend at your cruise mach no, then when your IAS equals your desired IAS for the descent, descend at that IAS.The comments about FL280 is about right - maybe a bit lower.Hope this helps,Ian

Agree with above. Set climb power and lower nose to accelerate to climb speed. Once at climb speed adjust rate of climb to maintain speed +/- 3 kts. Once climb mach is obtained, follow mach +/- .005 until cruise alt is obtained. Accelerate at cruise alt until cruise mach obtained, then set cruise power. Adjust cruise power as required for aircraft weight.scott s..

Depends on the company. it's generally around FL270-FL300 that you end up doing it, but the real answer is that you fly a target CAS until you reach the target mach. Our VA (based loosly off of America West/US Air's proceedures) has a 300/0.74 climb restriction. So we fly 300 knots, until 300 knots equals .74 mach, then climb at .74 mach.edit- I forgot to mention, that's for our 737-300 and 737-400s, I'm not sure on the other aircraft in our fleet yet.----------------------------------------------------------------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

I was also under the impression that, at least for the USA, it was IAS to FL 230 and then switch to MACH values above that. See the following link (last paragraph or two):http://avsim.com/geoffschool/combined/takeoff.htmhttp://www.graphics-free.com/animations/tr...ges/plane_6.gifAlex ChristoffN562ZBaltimore, MD

The actuall cross over height is defined by a particualr airlines SOP (Standard Operating Procedure). The chances are they will all be similar (as they all rip each others off to a degree) but it isn't valid to say "there be the level"

Actually it depends a lot on what you put in your FMS. With our Honeywell boxes the changeover happens right around FL 270 for our fleet. Its going to be pretty much identical for most airlines. The variation will only be slight and likely based on the temperature at altitude.Hornit

Thanks all for your answers.I was under the impression is was more regulated and defined than that.Still, learning all the time!CheersTim

No, it's pretty much how you want to do it. As I said, our VA with the 737 fleet climbs at 300 knots until reaching mach .74 then we maintain that for the rest of the climb. Most airlines generally have the same kind of proceedure, but it may be 315 knots then mach .75 or what ever pair of numbers they choose.----------------------------------------------------------------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