Beccazon
Crowing
The air sac is where it should be. No worries. In the picture they just used a basic oval shape but it should be at the fat end. If you take a pencil or some thing and mark The outline of the air cell, you can assess if it is getting larger as due date approaches. That is what you want. You would then know that it is likely progressing well since you are not able to candle in full darkness.