Large air cell on internally pipped chick under broody

[Weetamoo93]

I was checking on chicks under my 5th broody hen so far this year (my girls are NUTS) to see what had/hadn't hatched since they were due. 4 of 5 eggs had hatched and the chicks were already old enough to wander a little ways from Momma Minerva. I checked at night, candling the final egg. It was the one of suspected would have issues or not make it due to a small crack in the shell. It has a very large air cell. Immediately I thought "dead" and was planning how to dispose of it when I noticed a flicker of moment. I held it to my ear and could hear it pipping inside and tapping at the shell. When I was considering a safety hole, not finding where the tapping was located, I noticed a small new crack that light could just pass through, indicating the chick was working toward an external pip.

Has anyone seen an air cell like this under a brooding hen?

 

[Weetamoo93]

Got two more photos before my weather got more "fowl" (not sorry). The chick is very vocal and active inside the egg. My only concern is that the siblings are already hatched and about; all eggs were placed under hen at the same time and I check daily for any extras other hens try to slip in. Nobody has snuck one past Minerva, though.

One rather poor photo of the small crack it's had since about mid incubation and a second candling photo with markups: yellow arrow is wear chick appears to be working on external pip and red circle is approximate location of crack.

I could've managed a better shell photo if my daggum phone would actually work with me and focus and I want hurrying due to weather.