I agree. I am fairly sure that overstayers, just like if I overstayed in the US, might not be able to use the visa waiver programme. Contact the German consulate in NYC for clarification and don't rely on some random answers on the internet.

http://www.germany.info/newyork

I think at this point what I'll do is purchase a ticket from Frankfurt to Istanbul for the day I arrive, so I can claim honestly that I intend to use Frankfurt only as a transit point. I've been to Germany several times, and the only reason for attempting to visit on this trip was to be a short stop on the way to Asia. It just so happened that a one-way flight from JFK to Frankfurt was the cheapest way to go across the Atlantic. I intend on going on to Turkey anyway; it might have to be sooner rather than later.

Failing that idea, what do you think is the likelihood that I'll simply be told that I must buy the next ticket back to the US, no exceptions?

If you are transiting Frankfurt from a non-Schengen country to a non-Schengen country you will not pass immigration at Frankfurt.

That won't work assuming you have checked luggage because you would need to enter Schengen in order to pick up your luggage and check it in for the next flight. The only way to avoid this is to be connecting on the same ticket. If the airlines have an interline agreement they might check through on separate tickets but there is no guarantee.

Personally, if I was banned from Schengen I wouldn't go anywhere near a Schengen airport. It could lead to all kinds of complications including further bans if you try to be "cute".

So I'll be in deep s*** even if I make perfectly clear that I intend only to catch my next flight OUT of their country?

Is that right? Can anybody confirm this?

Banned means banned. You are not likely to be admitted under any circumstances. Once you are in you are in and could abscond.

But as noted before, the only real answer will come from the German authorities.

As a US citizen, you visit the Schengen zone as a guest. You did not comply with the rules and were apparently asked not to return for six months. It would be rather disrespectful to show up and expect them to let you through anyway, and your past overstay makes you less trustworthy in the eyes of officials than the average traveller. It's up to them to decide, but I doubt it would go smoothly!

I understand the fact that I'm likely banned and don't oppose that as a restriction on entering the Schengen countries. It's an annoyance but I did (unknowingly) break the law, and I should be held responsible.

But surely there is some kind of dispensation for those simply using an aiport and its facilities to travel onward to another destination? I am aware that one usually goes through immigration immediately after disembarking from the plane.

Is there absolutely no way I could try to get on a connecting flight to Turkey?

Contact the German embassy and ask the question. No one can tell you for sure.

However, as they did not make a big deal of it, and I would assume they are looking at it as an error, then I think you may be able to speak to the embassy and they will probably show leniency and give you a visa to stay and enter.

If however you don't do this and just front up, there is a high chance you will not gain entry.

So do it properly and you will probably be fine.