Here's how I understand it:
If training is to maintain the requirements of your current position, it is deductable. If the training is to gain qualification for a higher position with better pay, or a job that you don't currently have, it is not deductable.
So: if you were flying for a Part 91 outfit, and they required you to get your own flight review... deductable.
If you're a F/O with a CPL, and you get an ATP so you can upgrade, not deductable.
Something like a CFII is a little grey ... is it a new position? once you get the II? I dunno, is there better pay?
Anyway, that is my understanding, I'm not a tax attorney, and my recollection of it may be flawed. The IRS maintains a Website with information on Tax regulations. Go there and wade through the regs on deductions. see if you agree with me or come to a different conclusion.