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Trans LVL vs. Trans ALT

NYCPilot

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What are they and what are the differences between the two. When are they used and why.
Thanks.
 

Workin'Stiff

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If I've got this right, tran level is the altitde where you go from local altimeter settings to 29.92" or 1013mb and start flying pressure levels. Trans alt is where you switch from standard altimiter settings (29.92 or 1013) to local altimeter settings, hence reading MSL. I know in Europe that those two will sometimes be different. Here in the US, it's always 18,000'. I'm not sure why that is the way in Europe and other parts of the world...
 

Inida Job

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a little dyslexia never hurt anyone...

Stiff,
I'm pretty sure you have it reversed. The way I always remember is, if you are above 18000' you have 2992 set and you are flying flight LEVELS (ie FL190, FL250, etc.). As you descend you hit the lowest level available (FL180 in most cases in the US) also called the transistion level and you have to switch to local altitmeter setting. You are now flying MSL altitudes. As you climb up from below 18000' you hit the highest ALTITUDE available or transistion altitude (at 18000') and you switch to 2992.

I think 18000 is used in the US because of terrain and standardization. If you set 2992 above 18000 then you will always be above Pike's Peak or Mt Ranier (even Mt McKinley in AK) no matter what the local barometric pressure is. Airfields in south FL could safely use different trans levels and alts but FAA standardized so all the US would be the same. Not every country is the same. Some countries have different trans lvls and alts at every airport, they are published on the Jepps approach plate. The purpose of the different settings is to make sure the aircraft close to the ground all have the same local setting so they don't hit each other or the ground and aircraft up high (not so worried about hitting the planet) will not hit each other and they don't have to change altimeter settings every 30 miles.

To further muddle things up:
QNH-altitude above mean sea level based on local station pressure. This is "local" altimeter setting used below 18000 in the US.
QNE-altimeter set to 1013.2 millibars (standard pressure also 29.92 inches). The "standard" setting used while flying flight levels.
QFE-atmospheric pressure at Airport elevation. With its sub-scale set to the Airport QFE an altimeter will indicate height above that airfield. In other words, on the ground dial the baro pressure until the alt reads zero and you have QFE set.

If you do a yahoo or google search for "transition altitude definitions" you will find a lot more detail about altimeter settings than I could provide here (I've already gone longer than I wanted!).
 

Workin'Stiff

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Inida Job-

Thanks man... I was kinda shootin' from the hip anyways... Don't really use the terms here in the US... It's more like, "um, 92 set.." :)
 

NYCPilot

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So if I understand this correctly, the reason behind assigning a "Trans" LVL or ALT is predicated upon the requirement for switching from 29.92 to local altimeter setting and vice versa. Basically assigning an altitude or flight level based on when to change over. Although, normally it is ALWAYS 18,000 in the U.S.

Going from FL's to MSL my Trans LVL is 180...(U.S.)

Going from MSL to FL my Trans ALT is 18,000...(U.S.)

Thanks for the replies and correct me if I'm wrong.


.NYCPilot.
 

Workin'Stiff

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Yep, that's correct. It's nice and easy in the US.. Things get alittle more complicated when you're abroad...
 

Inida Job

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It can get slightly more complicated in the US also. If the local altimeter setting is less than 29.92 then the trans LVL can be higher than 180. In other words you may have to set the local altimeter before you reach 180 on the way down. There's a chart in the Flight Information Handbook for us NOAA/DOD FLIP users. Not positive where Jepps puts this info.
 

AdlerDriver

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NYCPilot said:
So if I understand this correctly, the reason behind assigning a "Trans" LVL or ALT is predicated upon the requirement for switching from 29.92 to local altimeter setting and vice versa. Basically assigning an altitude or flight level based on when to change over. Although, normally it is ALWAYS 18,000 in the U.S.

Going from FL's to MSL my Trans LVL is 180...(U.S.)

Going from MSL to FL my Trans ALT is 18,000...(U.S.)

Thanks for the replies and correct me if I'm wrong.


.NYCPilot.
An easy way to remember it is with the A in Transition Altitude looks like an arrow pointing in the direction you are going when you use it. Conversely, the V in Transition LeVel points in the direction you are going when you use it. I like idiot-proof stuff. ;)
 

Dr Pokenhiemer

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You will see Trans. Alt. down to around 7000msl (don't quote me or bust my chops if that's not exact) if you fly down around Bermuda. I think it's partly because of the lack of low-level radar coverage in that area. New York Center monitors you all the way to the tower handoff. Obviously there is no terrain to have to worry about over the ocean--could be another reason for being able to use 29.92 so far below FL180 as we normally do here. In case you were wondering, Trans. Altitude can be seen on the Jepp Charts usually just below all the Freq. info near the top of the page.
 

TonyC

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Transition Altitude is the highest altitude available.

Transition Level is the lowest flight level available.




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jetalc

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TonyC said:
Transition Altitude is the highest altitude available.

Transition Level is the lowest flight level available.




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Ummmm...no. Look at an approach plate - that's the transition altitude and FL they're talking about. Availability of the lowest FL depends on pressure in the area.
 

TonyC

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jetalc said:
TonyC said:
Transition Altitude is the highest altitude available.

Transition Level is the lowest flight level available.
Ummmm...no. Look at an approach plate - that's the transition altitude and FL they're talking about. Availability of the lowest FL depends on pressure in the area.
Ummm, yes.

The Transition Altitude published on the approach plate is the highest altitude available. You cannot fly or be assigned a higher altitude. Anything above that would have to be a Flight Level.

The Highest Altitude available, or Transition Altitude, is determined by the State Agency (that would be the FAA here in the US of A) and might be based on any number of variables.

The Lowest Flight Level available, or Transition Level, is also determined by a number of things, one of which MIGHT be the local barometric pressure. It might be a fixed Level, as it is in the majority of the US, or it might vary. Consequently, it may be published on the approach plate, or it may be part of the ATIS.

I tried to read the poster's question and answer it directly without branching out into complicated scenarios and exceptions. My answer was succinct and absolutely correct.


For a more in-depth explanation and discussion, try this. For an explanation tailored more for the non-pilot, Wikpedia's flight level should work nicely. To quote Wikpedia, "A vertical region extending from a defined transition altitude to the lowest available flight level is known as the transition layer - pilots will use altitude based on the local pressure below this level, and flight levels above. The altitude of the lowest flight level varies from country."



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