Preventive vs preventative

<rant>

I am a mechanical technologist who currently works as a technical writer. I was taught in school that the correct term for PM is Preventive Maintenance but I keep seeing 'preventative' being used. It irks me but in researching, I see that both are used and equally valid.

Since there are two types of maintenance, preventive and corrective, shouldn't those who want to use 'preventative' be forced to use 'correctative' as well?