Altitudes and flight levels
Thread Starter
Joined: Dec 2004
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From: London
Altitudes and flight levels
Good morning,
I should know this from my training. But I'm afraid I don't. So shamelessly asking for help here.
Altitudes and flight levels.
Suppose I was going to IOW/Sandown from my base at Rochester. Once clear of the London TMA, I can climb and climb and climb, - in fact, that's what many people suggest I should do.
At what point do I go from QNH to flight levels if I want to cruise at or around 6K? And do I need to worry about the circular rule?
I seem to remember (vaguely) that the transition altitude varies from one place to the next - but I'm afraid this is where my knowledge ends....
Thanks for advice!
I should know this from my training. But I'm afraid I don't. So shamelessly asking for help here.
Altitudes and flight levels.
Suppose I was going to IOW/Sandown from my base at Rochester. Once clear of the London TMA, I can climb and climb and climb, - in fact, that's what many people suggest I should do.
At what point do I go from QNH to flight levels if I want to cruise at or around 6K? And do I need to worry about the circular rule?
I seem to remember (vaguely) that the transition altitude varies from one place to the next - but I'm afraid this is where my knowledge ends....
Thanks for advice!
Last edited by agfoxx; 21st August 2018 at 08:23. Reason: typos
Joined: Feb 2001
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From: Lechlade, Glos.UK
Well, having my first solo in 1959 and left the RAF in 2003, my memory is fading so perhaps more learned pilots will correct me. But here goes: You change to 1013 at Transition Level which is normally 3000 feet QNH. In the USA, by the way, it is 18,000 feet. I think the London control zone use to be 4000 feet. I think quadrants are now gone and we operate semi-circulars.
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From: Wildest Surrey
Well, having my first solo in 1959 and left the RAF in 2003, my memory is fading so perhaps more learned pilots will correct me. But here goes: You change to 1013 at Transition Level which is normally 3000 feet QNH. In the USA, by the way, it is 18,000 feet. I think the London control zone use to be 4000 feet. I think quadrants are now gone and we operate semi-circulars.
A common transition altitude is being considered for the whole of the UK to bring it in line with other Eurocontrol countries, possibly either 10,000ft or 18,000ft but no decision has yet been made.
Hopefully the RPS system will be dispensed with when it happens.
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From: UK
Curious, I just tried to reply to an identically worded post on the Microlight page on Facethingy just disappeared as I was replying to it.
Not disputing anything stated above (apart from RPS, which I find handy), but a useful rule of thumb is to use the airspace limits shown on the CAA half million chart. Look at the airspace top and bottom marked in your general vicinity and similar altitudes. If it's in feet, leave QNH on, if it's shown as a flight level set 1013 and use flight levels.
Not an official method, but works well enough and has never got me in trouble.
G
Not disputing anything stated above (apart from RPS, which I find handy), but a useful rule of thumb is to use the airspace limits shown on the CAA half million chart. Look at the airspace top and bottom marked in your general vicinity and similar altitudes. If it's in feet, leave QNH on, if it's shown as a flight level set 1013 and use flight levels.
Not an official method, but works well enough and has never got me in trouble.
G
Joined: Aug 2001
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From: UK
Joined: Jul 2008
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From: london
To answer your question about the 'circular rule' - have a look here for a definitive explanation
https://www.caa.co.uk/Commercial-ind...mplementation/
https://www.caa.co.uk/Commercial-ind...mplementation/
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From: Wildest Surrey
Curious, I just tried to reply to an identically worded post on the Microlight page on Facethingy just disappeared as I was replying to it.
Not disputing anything stated above (apart from RPS, which I find handy), but a useful rule of thumb is to use the airspace limits shown on the CAA half million chart. Look at the airspace top and bottom marked in your general vicinity and similar altitudes. If it's in feet, leave QNH on, if it's shown as a flight level set 1013 and use flight levels.
Not an official method, but works well enough and has never got me in trouble.
G
Not disputing anything stated above (apart from RPS, which I find handy), but a useful rule of thumb is to use the airspace limits shown on the CAA half million chart. Look at the airspace top and bottom marked in your general vicinity and similar altitudes. If it's in feet, leave QNH on, if it's shown as a flight level set 1013 and use flight levels.
Not an official method, but works well enough and has never got me in trouble.
G
Joined: Feb 2007
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From: Amsterdam
A tip that I found useful: Your transponder will always show the flight levels, even below the transition layer. So you can use your transponder for two things:
- As your secondary altimeter when flying above the TL: It should give the same indication as an altimeter set to 1013.2.
- As a gross error check when flying below the TL: If the QNH is lower than 1013.2, then the transponder should indicate higher than the altimeter set to the proper QNH. If the QNH is high then the transponder should indicate lower than the altimeter. How much higher or lower? About 30 feet per hPa of course.
(I always get a brainfreeze when trying to remember whether the transponder should indicate high or low. The way I remember it is as follows: If the QNH is high, then the transition layer (from 3000' to FL35, say) is thicker (more than 500'). So if I'm climbing from 3000' to FL35, I need to climb more than 500'. This means if I arrive at 3000' and reset the altimeter to 1013.2, it needs to indicate 3500 minus a bit more than 500', so less than 3000'. For example, 3000' then becomes FL29. So with a high QNH the altimeter at QNH indicates more than the transponder (which is always at 1013.2).
This is useful when we fly aerobatics: Due to airspace restrictions we typically get a block between 3000' (below the TL) and FL55 (above the TL). Which is a block height of 2500' with a standard QNH, but less than 2500' if the QNH is low, and more than 2500' if the QNH is high.)
- As your secondary altimeter when flying above the TL: It should give the same indication as an altimeter set to 1013.2.
- As a gross error check when flying below the TL: If the QNH is lower than 1013.2, then the transponder should indicate higher than the altimeter set to the proper QNH. If the QNH is high then the transponder should indicate lower than the altimeter. How much higher or lower? About 30 feet per hPa of course.
(I always get a brainfreeze when trying to remember whether the transponder should indicate high or low. The way I remember it is as follows: If the QNH is high, then the transition layer (from 3000' to FL35, say) is thicker (more than 500'). So if I'm climbing from 3000' to FL35, I need to climb more than 500'. This means if I arrive at 3000' and reset the altimeter to 1013.2, it needs to indicate 3500 minus a bit more than 500', so less than 3000'. For example, 3000' then becomes FL29. So with a high QNH the altimeter at QNH indicates more than the transponder (which is always at 1013.2).
This is useful when we fly aerobatics: Due to airspace restrictions we typically get a block between 3000' (below the TL) and FL55 (above the TL). Which is a block height of 2500' with a standard QNH, but less than 2500' if the QNH is low, and more than 2500' if the QNH is high.)
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From: Amsterdam
Google "Garmin transponder" or "Trig transponder" on Google Images. Plenty results.
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From: Nanaimo (CAC8)
I fly aeoplanes from the dark ages. My transponder always says 1200’. 
PS All this nonsense and confusion would go away, if the transition altitude was 18,000', like on this side of the pond.
PS All this nonsense and confusion would go away, if the transition altitude was 18,000', like on this side of the pond.
Last edited by India Four Two; 22nd August 2018 at 06:57.
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From: Wildest Surrey
The transponder always sends altitude information to the interrogator based on 1013.2 and the radar display on the ground is set with the current local pressure setting and this converts it to altitude; that's all I l know.
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From: Wildest Surrey
Years since I flew with a transponder (no room for one in a Shadow microlight) so I'm obviously out of date.
Anyway I get my 'standby altitude' info from my Garmin handheld GPS which doesn't need an encoding altimeter!
Anyway I get my 'standby altitude' info from my Garmin handheld GPS which doesn't need an encoding altimeter!
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From: UK
Everywhere but North America mostly use 7000 "VFR, own navigation".
(Yes I do know the differences in practices between N.America and the rest of the world, but this particular one is funny and has occasionally embarrassed somebody who first learned to fly in the USA particularly).
G
