PHI Aircraft upgrade and transition contracts  

Depending on the state you live in, they may or may not be enforceable.  However, the "Employer" can turn the debt over to a collection agency.  A civil action will then occur, with a court order "freezing" your assets (If you have any) and placing a judgement on your current paycheck (if you have one).  Then you have to hire a lawyer to clear your issues, and that will cost more than your training contract would have.  So end the end, you have won the battle but lost the war.