I have a single-entry Schengen tourism visa from the Greek embassy, Greece and will be traveling to Athens. However, I have a flight afterwards from Athens to Germany (Cologne) with Pegasus airlines with a connection in Istanbul Sabiha Airport.
My question is, will I face any problems when entering Germany since my visa is only single-entry? My flight from Athens to Cologne is only connecting in Istanbul for an hour; I will not be checking in at Istanbul. Or will my flight from Athens to Cologne be considered as within the Schengen area since Istanbul is only for a connection at the same airport and with the same airline?