The company can use all sorts of reasons to select you to go. For instance they may decide to get rid of the rank of CSD and all CSD's could go. Or they may decide that those with the least number of types would go so you would have to be qualified and current on 747,777 and 767 to stay etc etc. I am not suggesting that they will do this but these would all be legitimate and legal ways to make a decision. Last in First Out would be highly unlikely to be used as a sole criterion as it can easily be construed as discriminating on the grounds of age. Length of service allied to some other criteria may be used.