In the past, for other employers, I have worked days off to cover last minute charters and so on- and been well rewarded for it. Here it is not to cover late changes and the unexpected but just to cover the normal day to day operation and the rewards are pitiful. The situation will never improve until the people right at the top realise they don't have enough crew and do something about it. Working a day off just makes the problem worse. Just say no! (Or don't answer the phone....)