I would be extremely cautious with mentioning a Schichtzulage, those have been ruled illegal by the highest german tax court quite a few years ago. If your airline still uses it better be quiet, otherwise it can blow up quite wide and cost both employees and company a lot of money. Besides, everything over 15% means that around half the work done by the employees is done at night or during weekends / holidays which is what airlines flying longhaul do, however in the case of easyjet i somehow doubt it.