I don't know the technicalities of the whole thing shamrock, I can't remember the exact wording reading the fte site but it tells that nothing is "guaranteed". I doubt Aer Lingus will give a letter guaranteeing a job to anyone as the individual could: a) not be successful in training and b) not end up with a role in Aer Lingus because Aer Lingus make it clear in the descriptions that any job offer is subject to the requirements of the airline at the time, now I know that it is extremely unlikely that Aer Lingus will not hire you after successfully completing training , but I'm sure you can see the reasons why Aer Lingus will not provide any guarantee so to speak. They most likely will give an offer of employment however they will say it is subject to many other things and their requirements at the time of your graduation.