sounds reasonable to me . A little excessive perhaps , but 3 years ? Should be quite proficient with about 1500+ on type by then , which will be very marketable .as long as there is a reasonable clause that allows you to leave on health grounds , being made redundant etc.
Bottom line is , you are not paying 50k$ , you will be paid quite well , acquire world-wide skills and experience , while working for a world class airline which is not going to diasappear ANYTIME.
lucky chap I say - couldn't do that when I were a lad.
enjoy it.