I wonder who uses both in Europe?
I know the UK uses both, and most pilots don’t know the difference. Outside the UK, where significant altitudes can be flown (e.g. the Adriatic goes to about 10000ft) they seem to use just the first one.
References to both can be found here.
I thought everyone uses both. I’m only aware of transition level being calculated dynamically as the lowest level that is at least XXX ft the transition altitude, but the value of XXX depends on the country.
In controlled airspace it’s processed by ATC for you? if you ask for FL40 on descent they will clear you for 4ft, if you ask for 6kft they clear you to FL60
Does it make any practical difference to PIC flying? (assuming one use QNH on his 2nd altimeter to avoid terrain)
In uncontrolled airspace, 3000ft amsl is used as default TA for semi-circular rule, TL has to be calculated by the pilot (again none of this should be an issue if 2nd altimeter is on QNH)
Define use?
I’m aware of both on every flight, but at the end of the day I can’t remember the last time when I really needed to know it myself, as altitudes and levels are usually assigned by ATC.
I quite commonly fly around 6000’ and depending where I am flying it’s not uncommon to get “G-CD can you adjust to FL60” and then maybe a while later “Can you adjust to altitude 6000’ QNH 1020” etc. By many books you shouldn’t really fly around in the transition layer, but it does happen in practice.
lionel wrote:
I thought everyone uses both.
Yes, everyone does.
I’m only aware of transition level being calculated dynamically as the lowest level that is at least XXX ft the transition altitude, but the value of XXX depends on the country.
AFAIK XXX is standardised to be at 1000 ft, so that traffic at the TA and at the TL are always separated.
Airborne_Again wrote:
AFAIK XXX is standardised to be at 1000 ft, so that traffic at the TA and at the TL are always separated.
France takes XXX = 0, according to AIP ENR 1.7.2.2.b:
- the transition level is «the first flight level, multiple of 10, equal to or superior to the transition altitude», that is, the first flight level read on an altimeter set to 1013.2 hPa, encountered by an ascending aircraft after crossing the transition altitude read on an altimeter set to the local QNH.
- the air space between the transition altitude and the transition level is the transition layer. Its thickness lies between 0 and 299 m (0 and 999 ft) depending on the ruling atmospheric pressure.
The discussion so far seems to be mostly related to IFR climbs & descents, which of course comes first to mind for IFR pilots.
There is another element that isn’t 100% related to transition altitude/level. Several (many?) countries delimit various airspace upper and especially lower boundaries using both altitudes and flight levels. This can be a trap for a (usually VFR) pilot, and can result in an airspace bust or worse (collision). Despite it being part of the PPL curriculum, many VFR pilots don’t need or use QNE/STANDARD very often if at all depending on where they fly, and are not always sensitive to its importance when flying under airspace with a floor expressed in FL.
A valid point. My local airport has a TA of 6000’ but the main airway leading in and out of it has a base of FL45, luckily (I suppose) few VFR pilots fly above 3000’ so it would rarely be an issue, but the only good ways of operating in the vicinity is either to get a clearance into it, or have two altimeters so you can have one on standard and one on QNH. I know if the QNH is high then you’re fine but operating that way will catch you out some day when the QNH is low.
Yes could be an issue for VFR but as long as you keep flying on QNH with good +500ft margin nothing bad can happen as FL floors will get pushed higher on hot days with high pressure…
It’s unlikely to fly VFR that high in cold days ISA-10C with low QNH < 995hp such that 500ft is not enough?
Most VFR rarely fly above 3000ft agl even in CAVOK ISA days 
None of this is an issue for traffic VFR/IFR in controlled airspace with radar and mandatory mode C tranponders, for terrain, VFR should have other means to avoid hitting terrain than high precision altimetry…
For busting controlled airspace (UK mainly) while flying uncontrolled bimbles, well some airspace is defined in AGL (QFE), some in MSL, some in FL (STD) all in the same map, the only way to comply is to have few baro altimeters to cover the various airfields and maybe a radar altimter
lionel wrote:
France takes XXX = 0, according to AIP ENR 1.7.2.2.b:
Interesting… That used to be the case in Sweden as well but I though that the change was harmonised by Eurocontrol.
