you have 2 possibilities :
-you can block a sum of money during 3 years equivalent to the price of the type rating, TNT have access to that money in case you will leave within 3 years, and will take the equivalent of what's left from your bond.
-If you dont have money to block, TNT will pay you 75% of the normal salary the 1st year and will redistribute this 25% taken the first year over 3 years (3 payments : at 12, 24, 36 months of employement)
of course if you leave the company before your 3 years bond you'll have to pay back the proportion of the cost of the type rating (and you will loose 1 third of your 25% of your annual salary if you leave after 2.5 years for example).