Would mean one less thing to think about for most GA ops. However, surely it will mean a re-definition of all airspace classified by flight level below FL180? People might need to start using ASR again. Would people still use the quadrangle rule?
What's a 'quadrangle rule'? After 40 odd years in ATC I never heard of it. As for using ASR; this would not necessarily prevent a pilot from inadvertantly entering CAS when operating below a CTA so I would think pilots would have to get an actual QNH, possibly from the nearest airfield, as they presently MUST do when operating below a TMA (FIR might be able to help but would they have the closest local value available?).
As a very occasional enthusiasist Flyer; I understand that QNH will give the PIC his height above mean sea level in the vacinity of an airfield. ASR when set will give the lowest expected pressure QNH for the region in which the setting applies for a given time - So assisting the pilot against a drop in actual atmospheric pressure, erroding minimum safe sector Altitude.
Given my very limited understanding of things like this - FL 1013 Mb (old money) is set as you pass "transition altitude" on departure to provide aircraft on "Airways" with a setting calibrated to ensure a 1000 ft seperation between aircraft.
OK I suppose modern aircraft climb through the proposed transition altitude comparitively quickly so no problem. But are there routes where even modern jet aircraft actually fly comparitively low (say 18000 - FL180) because of fixed height restrictions at given waypoints.
Can you imagine the complexity imposed in a country the size of the UK by flights transititing ASR's within airways with differiing regional settings - not to mention turboprops or perhaps a day where the isobars are tightly packed.
I know in the USA (a big country) the transition altitude is something like 16,000 ft but I imagine their ASR regions are a lot bigger.
Can you imagine the complexity imposed in a country the size of the UK by flights transititing ASR's within airways with differiing regional settings - not to mention turboprops or perhaps a day where the isobars are tightly packed.
FWIW because of the high TA/TL in the States and the complexity of some of it's airspace (especially the Eastern seaboard around BOS/New York/PHL/IAD) it's not unknown in the descent to do pretty much what you describe - to fly part of the descent, including STAR altitude constraints on one altimeter setting and then have to change setting when handed over to the next agency to continue downwards, eventually landing using the airport "altimeter"....not pretty but you just need to be ready for it.
In the US each new ATC sector gives you their altimeter setting below 18,000ft. It has the advantage about not having to worry about what you real altitude is versus flight level but it also means you have to change altimeter settings a lot.
On balance I don't like the way at the moment different parts of the UK seem to work on different transition altitudes, I can't see any good reason for it and it would seem sensible to just have one. The US uses 18,000ft so that seems as good as any other altitude to use...
When I started flying IFR you got a new transponder code (if they had radar) and and the altimeter setting at each check in. So now there is only half the work. Even doing 290 knots at 15,000 PHL to JFK it's just another 3 seconds for the controller and another few for the flight to reply. In a way it may help, when the flight replys "Two niner niner seven" you know that conversation is over and you can jump in.
The US uses FL180 as the transition altitude based on the highest terrain. I know the highest terrain in the lower 48 states is in California and is around 14,000ft. In my opinion, it is a system that works very well because on an IFR flight plan in controlled airspace, the controller always gives their latest altimeter setting in your area when you check on below FL180.
It would certainly be nice if all countries could adhere to one set of airspace rules and definitions, making our lives easier. I imagine it could sometimes get tricky to remember different terminologies and transition altitudes.
The UK regularly experiences deep low pressure systems. More so than most countries. The QNH can vary significantly over short distances.
A standard TA/TL, higher than current seems a good idea. But why FL180? There is no terrain higher than 5000 feet. FL 80 would seem more realistic. FL 180 for the whole of Europe perhaps?
Location: A Whilom nimble brain. With 31 million posts.
Age: 72
Posts: 2,957
Mmm . . . perhaps it's time for two distinctly different types of height information to be used. i.e. Standard all the time to stop aircraft bumping into one another, and a new display for terrain and airfield use.
This might have been nonsense once, but with modern flight-decks, the total separation of a theoretical spacing height, and a true working height, starts to make more sense.
No, I don't expect anyone to take this seriously. Keep twiddling that little knob.
Thanks Con. as I said earlier. correct me - Does the higher transition make your workload harder ?
Exactly the opposite. Setting QNH before or after you get busy is a good thing. Those wacky departures in the UK where every time you reach for a knob you get a radio call are spring loaded for missing that 4000 feet (or whatever) low transition altitude. Likewise, on the way down, if you miss the change to 996 hPa, you don't have much time to catch your mistake before you get a GPWS (or, so I'm told ).
A friend of mine from the UK is dismayed that many U.S. departures are now simple vectors, e.g. runway heading, maintain 5000 feet. I guess he still does NDB holding and stuff like that on his instrument check and doesn't like the simplicity.
If you have to change the altimeter more than once below FL180 in the U.S., it's a tweek since you've already set QNH and even if you miss a call, you'll usually be closer with the arrival ATIS value a hundred miles out than with QNE (sometimes in the NE U.S. you will be below FL180 a hundred miles out to get under another airport's corridors).
A friend of mine from the UK is dismayed that many U.S. departures are now simple vectors, e.g. runway heading, maintain 5000 feet. I guess he still does NDB holding and stuff like that on his instrument check and doesn't like the simplicity.
At least he will still be able to fly when the radar goes down!
But why FL180? There is no terrain higher than 5000 feet. FL 80 would seem more realistic. FL 180 for the whole of Europe perhaps?
Contacted,
The Transition Altitude for the whole of the US and Canada is 18,000', even though the vast majority of the terrain in both countries is below 3000'. It just makes life simpler.
As others have pointed out, when below 18,000, you are given new Altimeter Settings as appropriate (and they are NEVER referred to as QNH).
The system in the US really isn't that tedious most of the time. Once cleared below 18000ft during the descent, the controller will supply the QNH of a station within 100nm. Using the 3:1 rule, you'll see that by 18,000 you're nearly there anyway, so you only have to change it once or twice, and then maybe only by 0.01 each time.
).
