Morning,

 

On a lot of approach and departure charts I see both a Transition Altitude and a Transition Level, each with a different altitude. eg. Kathmandu (VNKT) Transition Level = FL150 Transition Altitude = 13,500.  What is the difference between the two,m and how and when does a pilot select which to use?  thnx!!!

 

Richard

Climb vs. descent.

 

If you are climbing then you pass through the transition ALTITUDE. If you are descending, then you pass through the transition LEVEL.

 

http://en.wikipedia.org/wiki/Flight_level#Transition_altitude

 

Best regards,

Robin.

Transition altitude is what you use when you're climbing out after departure and have local barometric pressure selected, Transition Level is what you use when you're descending from cruise level and have Standard Pressure dialled in. It is good conduct to switch between the two when either instructed to climb to a flight level on departure or descend to an altitude. ATC should give you the current local pressure before you get close to TL, if they don't hesitate to ask for it.

Got it gentlemen - thanks for the clarification.  One thing I like about this hobby of ours is that there is always more to learn, always a little more to pick up.

 

Richard

The altitudes between the Transition Level (TL) and the Transition Altitude (TA) form a buffer zone so that aircraft still on standard altimeter barometric setting can't fly at an altitude too close  to aircraft on local altimeter barometric setting.  An aircraft should never be cleared to an altitude between the TL and TA.  At or below TA the altimeter should be on local barometric pressure.

 

AFAIK, the TA is always fixed.  At some airports the TL varies according to the atmospheric pressure at the time.  For example, if the barometric pressure is very low, altimeters on standard setting will read higher than the real altitude.  If the TA is, say, 6000 ft, an aircraft still on standard altimeter could easily be at 6500 ft, only a few hundred feet above an aircraft on local altimeter setting at 6000 ft.   So on a day like that, to ensure adequate vertical separation, the TL would be set higher than on a day with standard or high actual barometric pressure.  Airports that have a standard TL presumably make it high enough so that even on a very low pressure day, aircraft on standard altimeter won't be too close to aircraft at or below the TA on local altimeter.

 

Mike

According to ICAO:

 

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

 

Transition Level is the lowest flight level available for use above the transition altitude. It varies with QNH, in principle.

According to ICAO:

 

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

 

Transition Level is the lowest flight level available for use above the transition altitude. It varies with QNH, in principle.

 

Some airports, like Kathmandu above and the one used for destination in the PMDG T7 tutorial have a fixed TL (they all have a fixed TA).

 

Mike

It's far easier to explain transition level/altitude with a picture. Note some people call the lower transition level (13000ft) as "Transition altitude". Level flight in the transition layer is generally not permitted.

 

 

This is only for New Zealand (except for the mountainous Mt Cook area and during extreme low pressure weather systems) so consult your charts for other countries/airports.

Some airports, like Kathmandu above and the one used for destination in the PMDG T7 tutorial have a fixed TL (they all have a fixed TA).

 

Mike

 

That doesn't affect the definitions of TA and TL. I also said TL varied with QNH in principle. As an earlier poster said, even the TL is fixed  it's based on an assumed QNH.

Fun fact:

Many people here (FAA-land) just assume it's always 18000/FL180 here, but it really isn't.  The difference is just that it isn't ever really explicitly stated.

 

If you're ever heading into JFK on VATSIM and hear this:

"Cross HOGGS at FL180."

...and then the next day:

"Cross HOGGS at FL190."

 

...it isn't the controllers screwing up.  The letter of agreement between ZDC and ZNY states that aircraft should be descended to the lowest usable flight level by HOGGS.  If the pressure is lower than 29.92, FL180 cannot be used (Google "lowest usable flight level" and you'll get a nice table, probably from the ATC "Bible," the 7110.65).  The transition level would then be FL190.  This is because at a lower pressure than 29.92, 18000 and FL180 don't match up as 18000 will be above FL180.

 

Here in the States, though, it's not generally something pilots pay much attention to.  ATC definitely keeps an eye on it in the ARTCCs ("Centers").  Dispatchers might, depending on the planned cruise levels for their flights, and pilots who have to plan their routes themselves may look at it.

Contrary to the US, I think it's a European habbit to have TA and TL set below 10.000ft (ofcourse unless airports are located in higher lands but I don't know any major EU airport located at high altitudes ASL)

 

Brussels for instance has a TA of 4.500ft

http://www.ivao.be/controller/general/approach

This is because at a lower pressure than 29.92, 18000 and FL180 don't match up as 18000 will be above FL180.

 

o.k., I understand.

So this is the reason why FSX/FS9 built in ATC always said "you are xyz feet above/below your assigned altitude! Climb/descend to FL180!" although I was flying the assigned FL180 on 1013/29.92.

Always very contradictionary...

other interesting fact

 

They are looking to harmonise the TA across the whole of Europe - but as you can imagine, certain european states are doing their usual version of Europe standardisation, in that the only like it if its what they do.

 

However the main proposal is that it will be 18000ft across all of Europe(or most of it) but either way you'll at least find that in a particular country you wont end up with multiple TA's depending on which airport you are flying into. 

 

http://www.caa.co.uk/docs/33/CAP%20493%20MATS%20edition%205.pdf section 7 and the appendix table will help explain ATC procedures within the UK - you'll see quite a lot of differences in how ATC is done in the UK and generally Europe to compared to the strange FAA stuff - things like clearing planes to land when there are already planes on the runway, and in fact planes ahead of you still on the approach! (kind of goes against the word Clear!) the closest the UK comes to that is at certain airports only they use phrase Land after the departing or Vacating. But never will you be cleared to land with something on the runway - and thats in use at the Busiest single runway operation in the world, so never worked out why a 8 runway airport in the states needs to clear everything! FAA ATC generally viewed as Air Traffic (limited Control) by most pilots outside of the USA.

 

 

things like clearing planes to land when there are already planes on the runway, and in fact planes ahead of you still on the approach! (kind of goes against the word Clear!)

 

It clearly works for us, so I don't understand why this continues to come up.  Additionally, the important word is "cleared" as in "you've been given clearance."  The literal definition of the word is "to give authorization to," not "to clear the way," as you've implied, but that's getting a little too deep into semantics.

 

 

 

the closest the UK comes to that is at certain airports only they use phrase Land after the departing or Vacating. But never will you be cleared to land with something on the runway - and thats in use at the Busiest single runway operation in the world, so never worked out why a 8 runway airport in the states needs to clear everything!

 

We clear people with anticipated separation because it works.  We don't feel that there's a reason to withhold clearance if there's reason to believe that the runway will be clear by the time you get to it.  I don't get why this is so much of an issue with people.

 

If we were smacking planes together all the time, then sure, but we're not.  Anticipated separation is only approved for use at certain facilities, and at those facilities, additional safety measures must be implemented.

 

It isn't as Shoot-from-the-Hip-Cowboy-Western-I'm-the-New-Sheriff-in-Town as people outside the States make it out to be.

 

 

 

FAA ATC generally viewed as Air Traffic (limited Control) by most pilots outside of the USA.

 

Over-control creates barriers, lack of dynamic adaptation, and generally gets in the way of efficiencies.  We just operate differently.  If there's some verifiable proof that ya'll are so superior, I'd like to see it.  I'd honestly like to see how that system would work N90.  That would be a sight to see...

 

Here, I think the mentality is more of "shared responsibility" than overt control.

,,We clear people with anticipated separation because it works,,

LOL unless it is a student pilot..... many decades ago I was cleared to land at KSAC Sacramento Executive and I nervousely watched an airplane on the runway ahead of me on his takeoff roll.... I executed a straight ahead go around and probably aroused some nervousness in the tower because I had to go talk to the chief controller after I shut down. I will never forget that embarrasment.