Originally Posted by geosch

I previously witnessed at TXL that a passenger flying from LHR to PEK via TXL, apparently without a Schengen visa, was asked to identify himself upon leaving the aircraft (BA at that time) and then was escorted (I guess by ground staff) to probably the appropriate departure waiting area of his onward flight to PEK (most likely on HU).
As you know, TXL was not built with international transfers in mind.
Why self-guided international transfers should not work at DUS, I don't know.