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Old 15th Sep 2004, 08:05   #1 (permalink)
 
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Post Transition Altitude and Transition Level

Ive been posed a question for an up and coming interview involving an approach into Bodrum and a possible conflict between two aircraft. Its between an aircraft holding at a flight level waiting to start the approach and an aircraft just starting the approach at an altitude......

How do Transition altitudes and levels prevent conflict? Also, two nice definitions of both please......

I think Ive got my head around it but........hearing from one more succinct than I would be great.

Cheers
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Old 15th Sep 2004, 10:15   #2 (permalink)
 
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Aileron, I suspect the reason you've had no reply in 3 hours, when everyone reading this forum knows the answer, is that they are puzzled as to what you are really asking. Because this is the sort of stuff that is taught almost on day one of a PPL.

Your profile is no help in finding your qualifications, so one doesn't know whether one has missed some nuance that would be puzzling a professional (there are always nuances!) or whether you are just starting out and don't yet have access to the books that explain it all. In which case, what's the interview for?

More background please, Aileron.
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Old 15th Sep 2004, 10:57   #3 (permalink)
 
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Vertical position of an aircraft at or below the Transition Altitude shall be expressed in terms of altitude relevant to the appropriate QNH setting. A climbing a/c will, at the TA, change its altimeter zetting to 1013.2mb.

The Transition Level is the lowest Flight Level (1013.2mb) available above the TA. At and above this level the vertical position shall be expresed interms of Flight Levels. A descending a/c will change its altimeter to the local QNH as it passes the TA.

There may not necessarily be any separation between the two but many ATC units will ensure that the lowest FL they allocate will be separated from the TA.

There... a pretty good guess without reference to any manuals!!!
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Old 15th Sep 2004, 12:16   #4 (permalink)
 
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Quote:
The Transition Level is the lowest Flight Level (1013.2mb) available above the TA...
There may not necessarily be any separation between the two...
Different states seem to have different views on this one. As HD says, the UK does not guarantee standard separation between the transition level and the transition altitude. I'm led to believe that other states do, however, taking a slightly different interpretation of ICAO's use of available. No idea about Turkey.
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Old 15th Sep 2004, 12:30   #5 (permalink)
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Here, we make sure that the lowest usable FL has the required separation from the highest usable altitude.

As for the definitions, I'll leave that to someone with the books at hand.

Regards,
Fred
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Old 15th Sep 2004, 14:32   #6 (permalink)

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In Aus, Transition Altitude is A100, (10,000') on QNH. Transition Level is FL110, (11,000') on 1013.2 hPa.

At a QNH at or above 1013.2, there is a minimum of 1000' vertically between the Transition Altitude and the Transition Level.

In an area of low pressure, FL110 is not available for cruis flight, to preserve the 1000' buffer between aircraft at A100 and aircraft above A100.

As the QNH drops, FL115 is not available if QNH < 997 hPa, FL120 is not available when the QNH < 980 hPa, FL125 is not available when the QNH < 963 hPa, and so on.
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Old 15th Sep 2004, 23:14   #7 (permalink)
 
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Cpt Claret,

Have no experience of flying in Oz, but your explaination of how things work does seem a bit strange.

In the UK, the TL is always physically above the TA by a maximum of 500' and minimum of 0'. Thus, a QNH of say 1010 with a 3000' TA will give a TL of FL35. Likewise, QNH 1016 in the same situation would give a TL of FL30. Thus, TL's are not generally published in the UK, navigation charts quoting "By ATC". In everyday operations, we would not even be told the TL as ATC take care of things.

As a result, seperation of a/c on STD and QNH is made simple - standard 1000' seperation by ATC guarentee's that the physical seperation will be at least 1000', possibly up to 1500'. I can't comment on other states, so forgive my ignornce!

Regards,

Cuban_8
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Old 16th Sep 2004, 02:46   #8 (permalink)
 
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I concur with claret on this one, if area QNH is lower than QNE, 1013 or 29.92 where I currently fly, then the lowest flight level (180) is usually not available. Minimum separation from oposite direction traffic is insufficient.
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Old 16th Sep 2004, 04:43   #9 (permalink)
 
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The US/Aust/Kiwi...rest of the world system as far simpler than the UK one.
(Having lived and flown in all of the above)

I remember flying from Weymouth towards Exeter...the acft ahead of me was at FL30 IFR, I was at 3000ft RPS VFR and the guys behind me was still using QFE, also at 3000ft.
Not impossible to work out by any means but ......!

The particular TA/TL in your part of the world is generally dictated by the MSAs.

Aust: 10000ft/FL110
NZ: 11000ft/FL130
USA: 18000ft/FL180

Aileron, your answer is in there......
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Old 16th Sep 2004, 08:56   #10 (permalink)

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Cuban_8

Horses for courses I guess.

Not having flown in the UK I find I have to think very carefully to assess the system you describe, whereas, being familiar with the system in Aus, where the TL is always FL110 and the TA is always A100, I find it simple.

Another way of looking at our system, is that rather than change the TL with changing (falling) pressure, we just prohibit cruise at certain lower FL to maintain a minimum 1000' buffer. The TL doesn't change though.
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Old 17th Sep 2004, 09:22   #11 (permalink)
 
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I would assume the definition of TA and TL are or should be the same everywhere. However I know that the TA varies in every country, and even varies within a country as well.

In Norway where I fly we have now set TA to 7000'. Before it was different for every airport you flew into. Some had 4000' some had 6000' and some had 7000' all depending on surrounding terrain. Now however every airport has 7000'. This altitiude is measured above the local QNH at that airport. Depending on the QNH and the difference to QNE the TL is set according to a table for every airport at any given time in order to ensure at least 1000' separation between the TA and the TL. On a day with very low QNH the TL would sometimes be as high as FL90 or even higher. On a day with QNH = 1013,25 HPa The TL would be FL80 and therefore have the 1000' separation between the two. As QNH drops the TL needs to be raised in order to maintain at least 1000' separation.

Someone stated above that an aircraft descending to land at an airport sets his altimeter setting to local QNH at TA is wrong. This is done at TL so that when he descends below TL he is flying on the same altimeter setting as everyone else flying below TA. Since the Transition Layer, the airspace between TA and TL is a greyzone in this relation, no aircraft is given clearance to fly in this layer. This is a transition layer and departing and arriving aircrafts are flying on different alitimeter settings. QNH for arriving and QNE for departing.
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Old 17th Sep 2004, 09:38   #12 (permalink)
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Why would anyone want to set QNE ?? All it gives you is the level which your altimeter will read at the specified aerodrome if 1013.2 is set on your altimeter. That's a lot of subscale changing to ensure the value remains constant

Much better to set the Standard Pressure Setting instead
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Old 17th Sep 2004, 10:49   #13 (permalink)
 
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I'm a bit confused ?!

QNH = is the pressure measured at an aerodrome reduced to sea level
QNE = Standard Pressure 1013,25
QFE = Is the pressure measured at the aerodrome
QFF = Is the pressure measured at sea level

QNH and QNE is the pressure used in aviation in Europe today. QNH below TL for arriving AC and for departing up to TA. QNE is used above TA for departing AC and above TL for arriving.

I'm not suggesting this is the best way of doing things, but it is the recognized way of doing it world wide.

In order to ensure that all aircrafts are flying enroute with the same pressure reference, QNE = 1013,25 is used. QNE is worthless when approaching an airport to land as all it gives you is your altitude above the 1013,25 reference datum. But enroute it's a good idea to use one standard as the pressure from departure to arrival can change alot.
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Old 17th Sep 2004, 11:21   #14 (permalink)
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QNE is NOT 1013.2 though, that is a misconception. Therefore you don't set it to fly a level datum.

When the ISA mean sea level standard pressure of 1013.2 hPa is set on an aircraft altimeter subscale, the height indicated on the altimeter upon landing at an airfield is known as the QNE.

QNE will always be a measurement of height, not of pressure. In standard ISA, the QNE would be 66' at my location.
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Old 17th Sep 2004, 11:44   #15 (permalink)
 
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I took this down from the web:

"QNE:
When the ISA mean sea level standard pressure of 1013.2 hPa is set on an aircraft altimeter subscale, the height so indicated upon landing at an airfield is known as the QNE reading. More widely, this is also the PRESSURE ALTITUDE, which is alternatively defined as the height of any level in the international standard atmosphere (ISA-see above), above the level corresponding to a pressure of 1013.2 hPa"

The question you raise is whether the QNE is the reading on the altimeter with standard pressure set, or if QNE is the actual pressure set. In the quotation above you can see that what you are talking about is "QNE reading"

This quotation is from an ATSB Accident report:"QNE is the standard pressure altimeter setting of 1013.2 hPa that is set for flight above the transition altitude."

All of the above; QNH, QFF, QFE and QNE are pressure settings and the abbreviation's can be found here :

http://www.aecma.org/Publications/glossary/gq.htm

But enough about that. The question here was the definition of TL and TA and how they prevent conflict. I hope those questions have been answered.
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Old 17th Sep 2004, 17:36   #16 (permalink)
 
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Smile

In answer to your question, it should not cause conflict in most countries however, what does the Turkish AIP say about changing altimeter settings? The best place to get an answer to that is in a briefing room of a UK airport used by the "Bucket and Spade" men where copies of other National AIP's are kept. I'd suggest that that the real answer would be that there would be a conflict (otherwise why the question - the interviewer will often want to show how clever they are) so the real issue is (as you politely praise the interviewer with his depth of knowledge) - How will you deal with the potential conflict (I bet you'll be a given a low QNH!)?
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