Transition Level

[JammedStab]

Is there a particular reason why there are two different transition levels in HKG depending on altimeter setting. Most other places seem to have one level such as Japan, Philippines etc.

[Yeager]

Some astronaut Cathay Pathetic senior C&T Captain will give you the "only right" answer to your curios question.

My humble answer would be; Hong Kong, as you know, used to be a POM Colony and as we all know, and as demonstrated by the Cathay Pathetic MNGM, they know "better". Why make it simple when you can make it hard.

Good luck with it!

[CokeZero]

JS

You referring to 9000ft to FL110 ? If so then this is common in most parts of the world. The gap I think you mention is a no fly transition zone to cater for very low QNH changes.

Does this help?
CZ

[Trafalgar]

...bit of a chip on your shoulder Yeager...??! Sheesh....take a valium mate. Type A or what...!

[BuzzBox]

The TL is FL110 with QNH 980 or above, FL120 with QNH 979 or below. It's to maintain a vertical separation of at least 1000ft between aircraft using QNH and those using QNE (1013) when the QNH is very low, eg during the passage of a typhoon.

If you recall, a pressure difference of 1 hPa is approx 30ft. Ergo, if the QNH is 980, the vertical separation between an aircraft at the TL and one at the TA is 2000 ft - [(1013 - 980) hPa x 30 ft/hPa] = 1000 ft (approx). If the QNH is less than 980, the separation between an aircraft at 9,000 ft on QNH and one at FL110 on QNE would be less than 1,000 ft. Hence a higher TL is used when the QNH is very low.

Fall foul of the system did we Yeager?? Can't say I'm surprised.

PS. FWIW, I'm not an STC, or an astronaut...

[JammedStab]

Originally Posted by BuzzBox

The TL is FL110 with QNH 980 or above, FL120 with QNH 979 or below. It's to maintain a vertical separation of at least 1000ft between aircraft using QNH and those using QNE (1013) when the QNH is very low, eg during the passage of a typhoon.

If you recall, a pressure difference of 1 hPa is approx 30ft. Ergo, if the QNH is 980, the vertical separation between an aircraft at the TL and one at the TA is (1013 - 980) hPa x 30 ft/hPa = 1000 ft (approx). If the QNH is less than 980, the separation between an aircraft at 9,000 ft on QNH and one at FL110 on QNE would be less than 1,000 ft. Hence a higher TL is used when the QNH is very low.

Thanks.

I'm just curious why the more complicated procedure instead of the straight forward single transition level that is used in much of the world.

As we all know...FL 180 in North America is the transition level, if the altimeter is below standard, then FL 170 not available from ATC. I'm sure both methods achieve the same thing.

Or the Philippines which has a space between the transition level and altitude like Hong Kong but still only uses FL130 for transition level.

[Vidab]

Buzzbox beat me to it, he is correct. The difference between HKG and other ATCCs is that they will take into account the low local QNH and simply not assign a low FL that would create a loss of vertical separation. All transparent to flight crew and with less risk.

I can just imagine a situation in HKG with a weak typhoon, low QNHs, saturated airspace and a few non-local crew missing that little gem of a note.

[fly123456]

In many european countries, the TL is not printed on the charts but is only given in the atis, as it is not fixed but varies with the local QNH.

[Absolutely Fabulous]

Code:

So the point remains: Why do they do it the hard way instead of the easy way? One guess!

because the older generation were taught to think but the younger generation taught to do ?

[White None]

Refer to Buzzbox for the facts. Of course we could just use FL120 all the time but then we'd lose 1000' (or arguably, with 2 way traffic, 2000') of manoeuvring space in the terminal area. If you think that would be "progress" suggest it and continue battering away on the keyboard without thinking. Or am I being "Silly"?

[744drv]

I don't really see how this affects flight crew in practise. If it is a sub 980 day your flight will not get cleared to a lower FL than 120 .... in which case you would stay on STD regardless of high/low pressure. Then when you are cleared to 9000' or below you 'transition'. The only difference between this and how LHR do it is that HK bothered to write their procedure on the plate; LHR do it seamlessly in the background .... same system.

[Steve the Pirate]

White None

Or am I being "Silly"?

Correct. Commendably self-aware. You must work on your sillyness and avoid the entirely reasonable, measured posts you keep ruining FH with - enough now, treat yourself, join in with a little tantrum.

STP