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Diego
Topic Author
Posts: 135
Joined: Mon Apr 23, 2001 7:33 pm

Transition Level

Mon Oct 21, 2002 12:31 am

Hi folks, yesterday I was cruising along at 410 on a Learjet 35 from KILM to KMIA when before starting the descent Jacksonville Center issued the following clearance 'NXXXX descend to FL 190 transition at 310 or greater'. As I was pitching down one question kept bugging me and it might be some of you may shed some light on it: although I know that the transition from mach to kias occurs between 280 and 310 depending on the temperature, I have never completely understood what causes that transition level to shift in altitude and if ther is any sort of rule of thumb to anticipate it. Thanks
 
Guest

RE: Transition Level

Mon Oct 21, 2002 12:43 am

Diego,
The transition happens when it happens. As you know, if you maintain a constant Mach as you descend, the indicated airspeed will increase steadily during the descent. At the point when the mandated IAS and the Mach held during the descent are equal is when you make the transition. As you can see, there are several factors in the equation - the indicated Mach in the descent, the OAT, and the assigned IAS given by ATC. You could probably come up with some sort of equation, but that would be too much unnecessary work; "somewhere between FL280 and FL310" is usually more than adequate.

Jetguy
 
Guest

RE: Transition Level

Mon Oct 21, 2002 4:29 am

Hello Jetguy and Diego -
xxx
You Gentlemen got me a little confused on wording here - Diego, that ATC clearance to me was just to descent at 310 KIAS or greater, down to FL 190... "nada mas"...
But what confuses me is you mention "transition" and "transition level"... we are talking about different animals here, Diego...
Is the "crossover" of Mach and IAS (Mmo vs. Vmo) the question...? That is strictly a question of your aircraft, if I remember, LR-35 is Mmo .82 IMN, and VMO like 358 KIAS... so you can do 310 or more, below the crossover...
The transition level (the title) confuses me... Any more question about it, come back here, Jetguy, myself or the gang will gladly explain it...
xxx
Happy contrails  Smile
(s) Skipper
 
Inbound
Posts: 614
Joined: Sat Sep 15, 2001 7:59 am

RE: Transition Level

Mon Oct 21, 2002 4:46 am

i thought transition level was an altitude where you switch from altitude in "feet or metres" to "flight levels"....and vice versa.
for instance in canada, it's 17999' or FL180
and here in trinidad, it's 4099' or FL041.
Maintain own separation with terrain!
 
Guest

RE: Transition Level

Mon Oct 21, 2002 5:27 am

Hello Inbound -
xxx
Yes you got the idea correctly - but watch out the definition's wording...
xxx
Transition altitude, is the altitude at which, when CLIMBING, you change altimeters from altitude in MSL (QNH) to flight levels (QNE) standard...
Transition level, is the level at which, when DESCENDING, you change altimeters from FL (QNE) to read altitude with altimeter set to MSL (QNH)...
xxx
Like you correctly say it is 18,000 feet in USA, most other countries is variable, can be as low as 3,000 feet MSL...
xxx
But I think our friend Diego was talking about the changeover from aircraft speeds expressed in Mach numbers or indicated speeds...
Happy contrails  Smile
(s) Skipper
 
Diego
Topic Author
Posts: 135
Joined: Mon Apr 23, 2001 7:33 pm

RE: Transition Level

Mon Oct 21, 2002 9:46 am

Thanks guys for your willingness, let's see if I can square that off, the clearance referred to the airspeed to maintain when transitioning from mach to kias, which as I know from my personal experience occurs between FL310 and 280, it did not refer to the transition altitude/level, that's why in the previous post I specified that I had been cleared to FL190 that as you know is 1000ft higher than the transition altitude, in this case. Now I was wondering if there is any rule of thumb or means to figure out at which FL the mach/kias takes place and basically why that happens, I have a general understanding of the reason although I haven't really ever understood it, Don't know why but a kind of tricky concept to grasp.
Thanks again
By the way Skipper what are the minimums to apply for the company you work for?
 
Guest

RE: Transition Level

Mon Oct 21, 2002 10:21 am

Hi Diego -
xxx
The crossover Mmo/Vmo for your Lear 35 (verify if .82 and 358 are red line for your aircraft) will happen at FL 230...
xxx
Suppose you like to cruise and descend at .80, and would like to continue your descend at 300 KIAS thereafter... here is the table for you -
Down to FL 305 you will be at March .80... thereafter, 300 KIAS...
xxx
Diego, I am an old timer pilot who still believes in the aviation slide rules, and I use the old Jeppesen CR-3... To provide the top answer I wrote to you, I did place Mach .82 on the Mach scale window, then looked in the CAS/PA scale, and found that for 358 KIAS, it is FL 230...
xxx
We may hire next year, presently ATPL written, 500 hours turbojet preferred, and Argentina citizenship, or Mercosur countries acceptable... if we cannot find such individuals, may take people from other areas. Italia e molto bene...
Ciao amico...
(s) Skipper  Smile
 
POSITIVE RATE
Posts: 2121
Joined: Sun Sep 16, 2001 11:31 am

RE: Transition Level

Mon Oct 21, 2002 5:02 pm

Here in Australia it is as follows: when passing 10,000ft AMSL(transition altitude) the pilot sets a QNH setting of 1013.2 Hpa and anything above 10,000ft is a Flight Level. When on descent approaching FL110(transition Level) the pilots sets area QNH. The altitude between 10,000ft and FL110 is the transition layer and it varies as temp and QNH vary.
 
User avatar
American 767
Posts: 4557
Joined: Wed May 19, 1999 7:27 am

RE: Transition Level

Wed Oct 23, 2002 9:23 am

In the United States, the transition level is always 17999ft MSL regardless of local weather conditions on the ground. As of 18000ft, altitudes are measured in Flight Level. If a pilot is assigned 18000ft as cruisting altitude, ATC will say Flight Level One Eight Zero, not eighteen thousand feet. Above 17999ft MSL, the altimeter setting is always 29.92 (measured in inches or mercury). And you have to be on an IFR flight plan to fly at 18000ft or higher, the airspace above that altitude used to be called the Positive Control Area before it was renamed Class A Airspace.

I don't know the aviation regulations in Australia at all, but when reading Positive rate's post, I think it is the transition level that varies according to temperature and QNH. If the local altimeter setting is close to 1013.2Hpa, the pilot will probably adjust it only when descending below 10000ft MSL but if it is farther away from Standard altimeter setting, the pilot will probably adjust it already when descending to 12000ft. I don't know, I imagine that's how it works.

I don't know what the transition level is in Europe but I do know it is lower than 18000ft. In Belgium, it may be even lower than 11000ft.

Ben Soriano
Brussels Belgium
Ben Soriano
 
Guest

RE: Transition Level

Wed Oct 23, 2002 9:37 am

Thanks American767 -
Taking good notes here about briefing - much appreciated -
Europe transition level lower than FL 110 - copied -
And varies according to TEMPERATURE and... QNH...
Thanks for the help, Ben...
About time that I finally learn something new... modern aeronautics I guess...
(s) Skipper
 
POSITIVE RATE
Posts: 2121
Joined: Sun Sep 16, 2001 11:31 am

RE: Transition Level

Wed Oct 23, 2002 5:47 pm

Regarding Europe i'm not 100% sure but i think that FL's start at 6,000ft. It is definitelty below 18,000ft you are correct about that American 767
 
FLY 8
Posts: 330
Joined: Sat Dec 02, 2000 5:48 am

RE: Transition Level

Wed Oct 23, 2002 6:08 pm

Like B747skipper explained correctly, there is a transiton level and a transition altitude.
The transition altitude is for an specific airport always the same for example 3000 ft. in Amsterdam. (It depends on the terrain surrounding the airport).
This transition altitude is always depicted on the departure charts.
Then we have the transition level, which is depending on the local altimeter setting. The transition level is higher than the transition altitude and only broadcasted on the ATIS.
Now in between the trans. alt and trans. level it is called transition layer. it is usually only about 2000 feet thick. At this altitude usually there should no airplane fly level.
yes i can handle that alone. - - -famous last words
 
Guest

RE: Transition Level

Wed Oct 23, 2002 6:15 pm

Getting better and better -
Now we are getting into experimental aeronautics as well -
What do we get next...?
I am not 100% sure either... but I am ready for anything at this stage...
(s) Skipper
 
Guest

RE: Transition Level

Wed Oct 23, 2002 6:23 pm

Thanks Fly8 - I was beginning to wonder what was going to be next...
(s) Skipper
 
VASI
Posts: 187
Joined: Thu Aug 17, 2000 3:33 am

RE: Transition Level

Thu Oct 24, 2002 4:42 am

That is correct. From 6.000 feet on you talk of Flight Levels in Europe.
Transition Level varies, will be given in the actual ATIS, but at least when reaching FL100 you have to switch over to 29.92 or 1013,2.
What a pitty, I usually never get higher than 4.000 feet in my Cessna/Reims 152. Highest was FL110 (climb rate at this altitude was still 200 feet per minute as I remember correctly  Smile )

VASI
 
Guest

RE: Transition Level

Thu Oct 24, 2002 5:07 am

I would like to ask friends here to be careful making statements which are erroneous and incorrect... 6000 ft is not a blanket European transition altitude... a transition altitude can be ANYTHING from 3,000 feet up, and varies. A transition level can be as low as FL 45 and as high as FL 200, and each country in the world have different applicable numbers.
xxx
Change from QNH to QNE and vv. is a very strict procedure and there is no such things as saying "about", or "I am not completely sure but..."
xxx
Altimetry is an exact science... ask those you flew against mountains or ground obstacles on approaches... it is not a "two lines" explanation, or a "one minute" briefing... I can make 8 hours classroom lecture about altimeters, the settings, the procedures, the errors...
xxx
Please let's avoid broadcasting errors - thank you...
(s) Skipper  Smile

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