My own dictionary lists preventive as the "correct" spelling, while it was written in 2000 or 2001 and is rather British. Truth is hard to find when it comes to Languages or even linguistics, so I gather other dictionaries disagree with that I wrote above.
As for your rant a page before, I would partially agree. (And yes, I read it and care about your opinion

) I wrote "partially" because I cannot speak of how English-speakers felt when coming in France for obvious reasons. I don't know about your hypothesis to explain this hostility or at least, this distrust from the French government, which would be linked to the choice of an "universal" language to be used in airports . To use English as the basic language in such cases is sensible IMO, simply because English is speaking much more widely than French to begin with. French was perhaps an universal language before, but that was five or six centuries ago so.
Nevertheless, I have to admit French usually have an issue with English, many barely know this language, and there are some who, even if they are fluent in English, are reluctant to use that language. I'm wondering, is such an attitude common in other countries or is that yet another oddity of France?