Gnomon
Topic Author
Posts: 894
Joined: Thu Jun 03, 1999 12:38 pm

Transition Altitude?

Mon May 22, 2000 11:08 am

I've noticed on several European nav charts the specification for "transition altitude." I'm assuming that the transition altitude is simply the altitude at which the altimeter setting is changed from the cruise QNE (1013.2) to the local QNH...

Is this correct?
 
Guest

RE: Transition Altitude?

Mon May 22, 2000 11:25 am

Yup you got it...

Climbing you'd set 1013.2 going through the transition altitude, descending you'd set the local altimeter setting.
 
sabenapilot
Posts: 2442
Joined: Sat Feb 26, 2000 6:18 pm

RE: Transition Altitude?

Tue May 23, 2000 2:00 am

To be fully correct-
Transition ALTITUDE is the altitude at which you set 1013.25hPa when climbing out.
However, during your descent, you change to local altimeter setting when passing the transition LEVEL. This is also written down on the charts, but is says something like 'by ATC'. ATC will tell you what the transition level is. Transition Level is always higher then the transition altitude and depends on the pressure. It changes from hour to hour, that's why they can't publish it.
Nowadays, the transition level is hardly ever used, because there's a rule that says that when you're cleared for a descent from above the transition level to below the transition altitude, you can change to local altimiter setting right away. Since most descents are uninterupted , this is almost always the case.

An example/
You're at FL120
Transition Level = FL50
Transition Altitude = 4500ft
ATC tells you to descent to 3000ft, 1018.
You can set 1018 right away and start your descent.
Or, you can descent and when crossing the Transition Level set 1023 on condition ATC has told you what the Transition Level is.
 
sabenapilot
Posts: 2442
Joined: Sat Feb 26, 2000 6:18 pm

RE: Transition Altitude?

Tue May 23, 2000 2:03 am

I've just written:
Or, you can descent and when crossing the Transition Level set 1023 on condition ATC has told you what the Transition Level is.
It should read:
Or, you can descent and when crossing the Transition Level set 1018 on condition ATC has told you what the Transition Level is.
Now it's absolutely correct  

 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Transition Altitude

Tue May 23, 2000 6:05 am

In North America, the Standard Pressure Region exists at and above 18,000 feet ASL and all low-level airspace in Northern Domestic Airspace (NDA). The object is to always have the altimeter setting while in the altimeter setting region (more in a moment), so climbing out, one leaves the assigned altimeter setting until in the FL airspace. On descent as mentioned above, one sets the assigned altimeter setting prior to entering low level airspace.

In Canada, we also have a horizontal requirement for setting standard pressure on our altimeters, and that is in the low level airpsace in the NDA region. The same logic applies horizontally as well as vertically: crossing the border from Southern to Northern Domestic Airspace, one leaves the current altimeter setting until inside the NDA, then switching to 29.92". Going the other way, one sets the current altimeter setting prior to exiting the NDA.

One big difference here is being alert for low pressure situations (altimeter settings less than 29.92"). It can get you in a heap of trouble. It is not uncommon to see very low pressure in Canada's eastern arctic, less than 28.20" on occasion. That's a difference of about 1700' of true altitude, not to mention cold weather altimeter setting source problems. There are also a lot of big rocks (~8,000') in the east & northern arctic region.

Another thread!

Best Regards,

Buff

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