Causes of chicken hatching problems

Our first trial hatch in the Brinsea Mini Advance incubator was better than I'd expected but worse than I'd hoped.  Four eggs  out of seven pipped, two chicks hatched, and one survived.  Although it was emotionally tough, I chose to autopsy all of the dead eggs in hopes of improving my hatch rate for next time.

• One chick was speared by another's claw as it tried to hatch.  The dead chick was hatching about half an hour later than its sibling and had just reached the stage where it was beginning to push the mostly detached egg top aside when its precocious sibling clambered over top of it and stuck its foot inside the crack.  In a way, this is a crazy fluke, but the experience also makes me think that it might be smart to have somewhere else for newly hatched chicks to fluff out rather than on top of their hatching siblings.  Since I've read that it's best not to move chicks to the brooder until they're fully fluffed out, that means a spare incubator or other enclosed, warm space.
  
• Another chick started pipping, but only seemed able to push small chips out of its shell.  (I've enlarged the hole after death to see in.)  I don't know whether the shell was abnormally hard or the chick was abnormally weak.  I'd read not to help chicks out of the shell, so I stood back, and the chick eventually perished (perhaps in part because an earlier hatched chick (not the same one as above) rolled the egg over so that the hole was face-down on the ground.)  Since the chick died anway, I wonder if I wouldn't have been better off helping this obviously struggling chick?  On the other hand, it might have come out weak and had to be culled anyway.
• Three eggs had nearly full-formed chicks inside but they didn't manage (or, apparently, even try) to pip.  Some sources suggest that late stage dead in shell chicks are signs of incorrect humidity, often too high.  I didn't keep track of the size of the air pocket over time by candling, but I may try that next time around to help me keep the humidity in the right range.
• Finally, one chick hatched on day 22 but died less than a day later.  Chicks that hatch late and are "soft" are indications of the average incubation temperature being lower than optimal, and temperature was definitely the spot where I did the worst job during incubation.  Air temperature in the kitchen fluctuated between 45 degrees and 85 degrees and the incubator's high and low temperature alarms went off several times.
  

The good news is that all of the eggs were viable and made it nearly to hatching time, which means our rooster and hens are all fertile.  And watching the first chick hatch was quite an experience --- well worth the price of the incubator by itself!  Hopefully I can fix my mistakes and have more living chicks next time.

Since writing this post, I've experimented much more with incubation.  I developed a dichotomous key that makes it easy to figure out exactly what went wrong (and how to prevent the problem from reoccurring).  Learn more about troubleshooting the hatch in my 99 cent ebook.

Permaculture Chicken: Incubation Handbook walks beginners through perfecting the incubating and hatching process so they can enjoy the exhilaration of the hatch without the angst of dead chicks. 92 full color photos bring incubation to life, while charts, diagrams, and tables provide the hard data you need to accomplish a hatch rate of 85% or more.