A GS is double pay, no credit IF (!!!!!) all the rest of your flying for the month is at or above the GS trigger. (This is for regular lineholders; the rules for reserves are quite different but that is another conversation.)

If you are below the GS trigger, the first thing that happens with your GS is that any time that is required to bring you up to the trigger is first paid out at straight pay and credit. In your example the first 30 minutes of the GS would be straight pay and credit, and the rest is double pay and no credit.

Two VERY important points:

1. As stated, you can borrow up to five hours from your bank to "fill up" to the trigger. So in your example it would be far better to take 30 minutes out of your bank to bring yourself up to the trigger; that way the GS would pay double for all of it.

2. GS accounting is not done until the END of the month. So if you have a GS at the beginning of the month, and your are way short of the trigger, not to worry. In addition to the five hours from your bank available to you, you have until the end of the month to white slip, swap with the pot, or use the swapboard to get your total non-GS hours up to or above the trigger.