How does schengen clean work? Like how would a airport segregate one of those flights? Which countries are considered "Schengen clean"?

They are segregated via either the terminal they use or if a mixed terminal the gate and how it’s set up to divert “clean” passengers one way and “unclean” another way.

Where did you hear the term "Schengen clean"? I've lived in the Schengen area since it existed and I've never, ever heard it. Anyway, read the Wikipedia article, where you'll find absolutely everything a non-lawyer needs to know, including a short "air travel" section.

Never heard the term.

There usually separate terminals for Schengen and non-Schengen flights, or at a minimum, a separate bank of gates where passengers can be segregated.

Pretty standard across the world (except the US). This means people en transit from a non-Schengen to non-Schengen destination don't need to go through passport contr�le; as they're not entering the espace Schengen.

Schengen considers arrivals from all the other schengen countries clean, so you avoid reclearing security. There different ways this is done depending how the airport is set up, but usually means you disembark the plane straight into the departure area for flights to schengen countries

There are some other countries that schengen considers clean, such as the USA and UK, but not every airport is able to ensure passengers from those countries do not mix with arrivals from unclean for example at passport control, so reclearing security is not always consistent, even across one airport. If my flight from london arrives into Terminal 1A at Frankfurt then no need to reclear security. If it arrives into T1B then I might.

meanwhile an arrival from london into warsaw, i would need to reclear security if going for a domestic or schengen flight as I mix with 'unclean' arrivals at passport control. If i am connecting to a non schengen flight then no need to reclear security as they allow you directly into the departure area from the jetty on production of your boarding pass.

Hope this helps. If you would like more info then share the flight details

At some airports if your flight is "clean" you will be directed at the jetway directly to the departures level (for transit passengers), otherwise transit passengers will be directed to the arrivals level for subsequent transfer processing. Usually arrivals and departures are on 2 different levels.

Singapore Changi is an example of an exception to this (I know it isn't Schengen). At Changi arriving and departing passengers mingle in the same spaces and this requires departing security at the gate.

[MENTION=747616]scottishpoet[/MENTION] I think no matter if you are schengen clean, if you reach passport control and releaize you are doing a ITI transfer, you will need to reclear transit security because you have left the schengen clean hallway

depends on the airport set up, in frankfurt you can transit clean (US and UK arrivals in Z) from non schengen to schengen via passport control

similarly in MUC

What is an "ITI transfer"?

While I don't use that term, I guess the poster meant International to International.

T-WDPLUA?

PS In case nobody understands, Thanks-why do people love using abbreviations? Are they so busy that they want to save a few seconds spelling words out? Do they wish to train our cognitive skills (thank you). Do they think this is the correct Internet etiquette?

Abbreviations are an efficient way of standardizing jargon so that people don't end up using different phrases to mean the same thing, which can cause more confusion than using an abbreviation ever would. In this way they make discussions more clear in the long run, even though they do require newcomers to familiarize themselves with the argot.

They also, of course, serve as an in-group identifier that helps the audience to recognize how familiar the speaker/writer is with the subject matter, which in turn often subtly affects how seriously their points are taken.

Yes, especially when people invent their own abbreviation! Sorry for the out-of-topic (OOT?) discussion, but in one of the common Internet sites explaining abbreviations there are 46 listings for ITI, but the one suggested by [MENTION=908768]ISTFlyer[/MENTION] (which, by the way, seems to be the correct one ) is absent! So much for "making discussions more clear" for me as a "newcomer".

The EU also recognizes the air security screening of Canada and Singapore as well, and has signed mutual recognition agreements with both countries.

Google works quite well for me when I see unfamiliar terms. For example, when I searched for "iti transfer", the first three search results were about exactly that, and then further down the page there were four links to FlyerTalk threads about it, with lots of detail