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Author Topic: transitional level vs transitional altitude  (Read 4365 times)
kaycekwon
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« on: March 15, 2014, 02:36:02 AM »

okay so my professor has possibly close to 30 years of experience in ATC but he's definitely not gifted in his teaching ability.

He has explained the difference between TL and TA and I can't seem to be able to grasp the concept.

I can't even begin to translate his lecture on here for you guys to analyse. He kind of said that we should look at Transitional Level as some type of platform? maybe?

Could you please clarify the difference for me? FYI the transitional level in korean airspace is FL140 or 14000ft
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kaycekwon
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« Reply #1 on: March 15, 2014, 02:49:23 AM »

I've looked up the definition on Skybrary but I can't seem to figure out what it means in the real world

Transition Altitude. The altitude at or below which the vertical position of an aircraft is controlled by reference to                  altitudes.

Transition Level. The lowest flight level available for use above the transition altitude.

Transition Layer. The airspace between the transition altitude and the transition level.
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1053857
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« Reply #2 on: March 15, 2014, 06:45:19 AM »

Transition altitude is when you're climbing you would switch from local QNH to standard QNH (1013).
Transition level is when you're descending you would switch from standard QNH to local QNH
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klkm
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« Reply #3 on: March 15, 2014, 08:15:08 AM »

http://en.wikipedia.org/wiki/Flight_level
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tyketto
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« Reply #4 on: March 17, 2014, 01:35:17 PM »

okay so my professor has possibly close to 30 years of experience in ATC but he's definitely not gifted in his teaching ability.

He has explained the difference between TL and TA and I can't seem to be able to grasp the concept.

I can't even begin to translate his lecture on here for you guys to analyse. He kind of said that we should look at Transitional Level as some type of platform? maybe?

Could you please clarify the difference for me? FYI the transitional level in korean airspace is FL140 or 14000ft

The others here pretty much nailed it.

I would venture to say that your instructor is US based (I may be wrong), because we have it a bit easy here, as our TL is are TA, so it is standard at FL180. So you should never hear '18000ft' being used by ATC. Even when the altimeter/QNH drops below 29.92/1013, you still should never hear '18000ft' being used by ATC.

BL.
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martyj19
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« Reply #5 on: March 17, 2014, 02:48:01 PM »

I must take issue slightly with tyketto ... as I understand transition level, it is identically equal to what FAR 91.121 calls "lowest usable flight level", so is not constant in the US, but varies with local altimeter.  91.121 has a table that specifies transition level varying from FL180 to FL210.  The transition altitude is 18000 MSL anywhere in the US.

To the original poster, the reason why a flight level may be unusable is that at low local atmospheric pressure, you would find that if you set your altimeter to standard pressure and fly 18000 on the altimeter, which is how FL180 is defined, your true altitude drops below 18000 and you are in conflict with traffic flying below 18000.   The solution is to block out use of any flight level that results in a true altitude below the transition altitude.  The saying is "High to low, look out below".

The same applies if you are on an instrument approach.  If you are flying it with an altimeter setting that is higher than actual conditions, you are too low and may hit something.  This is why some approaches say, "when local altimeter setting not received, use (some other) altimeter setting and increase (specified minimums and visibilities)" to compensate for the fact that you may in fact be too high or too low.
« Last Edit: March 17, 2014, 03:16:47 PM by martyj19 » Logged
tyketto
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« Reply #6 on: March 18, 2014, 01:12:43 PM »

I must take issue slightly with tyketto ... as I understand transition level, it is identically equal to what FAR 91.121 calls "lowest usable flight level", so is not constant in the US, but varies with local altimeter.  91.121 has a table that specifies transition level varying from FL180 to FL210.  The transition altitude is 18000 MSL anywhere in the US.

To the original poster, the reason why a flight level may be unusable is that at low local atmospheric pressure, you would find that if you set your altimeter to standard pressure and fly 18000 on the altimeter, which is how FL180 is defined, your true altitude drops below 18000 and you are in conflict with traffic flying below 18000.   The solution is to block out use of any flight level that results in a true altitude below the transition altitude.  The saying is "High to low, look out below".

The same applies if you are on an instrument approach.  If you are flying it with an altimeter setting that is higher than actual conditions, you are too low and may hit something.  This is why some approaches say, "when local altimeter setting not received, use (some other) altimeter setting and increase (specified minimums and visibilities)" to compensate for the fact that you may in fact be too high or too low.


Actually, a bit off.. the lowest usable flight level does not equal the transition level or transition altitude. That that just means that that particular flight level can not be used for flight. In other words, from 28.92 to 29.91, FL180 can't be used for any flight at cruise; FL190 would be the lowest usable flight level. But that doesn't mean that FL180 isn't the transition level or transition altitude. Same applies for between 27.92 to 28.91, when FL190 can't be used for a flight at cruise and FL200 becomes the lowest usable flight level. FL180 would still be the transition altitude.

I'll still hear ATC tell pilots to climb and maintain FL180, when the altimeter setting is 29.89. But that is because FL180 isn't their final altitude. In short, flying through that flight level doesn't mean that it can't be used for the transition level or transition altitude.

BL.
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martyj19
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« Reply #7 on: March 18, 2014, 04:46:11 PM »

I must take issue slightly with tyketto ... as I understand transition level, it is identically equal to what FAR 91.121 calls "lowest usable flight level", so is not constant in the US, but varies with local altimeter.  91.121 has a table that specifies transition level varying from FL180 to FL210.  The transition altitude is 18000 MSL anywhere in the US.

To the original poster, the reason why a flight level may be unusable is that at low local atmospheric pressure, you would find that if you set your altimeter to standard pressure and fly 18000 on the altimeter, which is how FL180 is defined, your true altitude drops below 18000 and you are in conflict with traffic flying below 18000.   The solution is to block out use of any flight level that results in a true altitude below the transition altitude.  The saying is "High to low, look out below".

The same applies if you are on an instrument approach.  If you are flying it with an altimeter setting that is higher than actual conditions, you are too low and may hit something.  This is why some approaches say, "when local altimeter setting not received, use (some other) altimeter setting and increase (specified minimums and visibilities)" to compensate for the fact that you may in fact be too high or too low.


Actually, a bit off.. the lowest usable flight level does not equal the transition level or transition altitude. That that just means that that particular flight level can not be used for flight. In other words, from 28.92 to 29.91, FL180 can't be used for any flight at cruise; FL190 would be the lowest usable flight level. But that doesn't mean that FL180 isn't the transition level or transition altitude. Same applies for between 27.92 to 28.91, when FL190 can't be used for a flight at cruise and FL200 becomes the lowest usable flight level. FL180 would still be the transition altitude.

I'll still hear ATC tell pilots to climb and maintain FL180, when the altimeter setting is 29.89. But that is because FL180 isn't their final altitude. In short, flying through that flight level doesn't mean that it can't be used for the transition level or transition altitude.

BL.


Okay, gotcha.  There is certainly no dispute that the transition altitude is 18000.  There does not seem to be a lot of operational difference no matter how the transition level might be defined.  At cruise in the usable flight levels, you are securely inside Class A and there isn't any conflict with unidentified VFR.  It would seem there is no difference between climbing/descending IFR traffic through 15000 or 17000 or whatever cruise altitudes above 18000 are blocked out by the local altimeter, while maintaining separation with whatever unidentified traffic there might be at those altitudes; I agree with that.

As long as you set standard pressure sometime during the climb through the transition altitude, and set local altimeter sometime during the descent, that suffices -- the exact altitude at which you are during a climb or descent is not material until it is time to level off at the cleared altitude.
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tyketto
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« Reply #8 on: March 19, 2014, 01:30:23 PM »

Okay, gotcha.  There is certainly no dispute that the transition altitude is 18000.  There does not seem to be a lot of operational difference no matter how the transition level might be defined.  At cruise in the usable flight levels, you are securely inside Class A and there isn't any conflict with unidentified VFR.  It would seem there is no difference between climbing/descending IFR traffic through 15000 or 17000 or whatever cruise altitudes above 18000 are blocked out by the local altimeter, while maintaining separation with whatever unidentified traffic there might be at those altitudes; I agree with that.

As long as you set standard pressure sometime during the climb through the transition altitude, and set local altimeter sometime during the descent, that suffices -- the exact altitude at which you are during a climb or descent is not material until it is time to level off at the cleared altitude.

Exactly. Depending on that altimeter setting (if under 29.92), there could be a 1500ft to 2500ft altitude block that is unused that separates VFR aircraft at the ceiling of their operating altitude, and the lowest altitude to be used by aircraft in Class A airspace.

Though if FL210 is the lowest usable flight level that can be used, you're probably in the middle of a hurricane, so do you really want to be up there anyway? Wink

BL.
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