Sorry to shatter your hopes, but if you have to ask for help as to how to make the distinction between a Line and Hangar based Engineer, then your chances of success at the Tribunal are less than zero. Doesn't say much for your legal representation either.
Much depends however, on why you are being transferred. Breach of contract ? personality clashes ? poor performance--your own that is ?----to offer but a few examples. If the issue is that you simply do not want to work in the Hangar--and your employer has decided otherwise, then you really have no case. you will simply join the ranks of the numerous others who have been transferred over the years from one working environment to another against their wishes.