Apparently they offer two options via the two contracting agencies - either 'worldwide', where you tell them when you want to work, and they either use you or not. Or fixed roster (21 on/14 off, or 24 on/12 off), which is fixed for the next 12 months. In the latter case you know how much you're going to get paid even if you're sat in the hotel not being used. In either case, the pay is about 500 usd per day 'on base', which is probably the lowest paid 747 captain salary in the market. Around 8000 usd per month. Other players pay up to double that, with benefits.