I am working for an Oregon employer as an aircraft mechanic. They want to send me to school to become more efficient on a certain type of jet engine. They are wanting me to sign a promissory note saying that I will stay employed with them for a term of one year otherwise I will be forced to pay back the amount of the school costs and other costs accrued with interest.

These agreements are not at all uncommon. You will need to show the exact agreement to a local attorney to determine whether or not the agreement your employer wants you to sign is enforceable in your state.