I recently have had to do some repair /replace work and I have had to do a lot of rivet removal.

I thought I would share a little info on this subject

 Most  of the rivets on Zenith Aircraft are the Avex blind rivets .  A4 or A5 in size

I have found that the A5 are a little easier to remove that the A4s.

 You just want to remove the head and not try to dill it all the way out . Most of the time when you remove the head the reat of the rivet will easilly come out ,but not always  A lot of the times on the A4 you have the madrel breaks off higher or even with  the head of the rivet. If you try to drill off the head with the high mandrel rivet, the drill bit

 will not want to drill into the harder mandrel and will wonder off the side of the rivet and make the hole oblong .

That will ruin the part .

Most of the time you can tap out the mandrel or at least make it lower than the skin and then the heard of the rivet can easilly be drilled off. Making the removal of the part easy.   Do not tap too hard or support the piece ,rib flanges are not strong enought to support a lot of pressure on then and you will wind up with a flange that will need straightening.

   You will then be left with the body of the rivet that you can try to remove with a side cutters.

 I have flattened the one side of mine to get the face tighter to the skin and easier to pull out the body of the rivet

 another method on that is to try to use the side cutters to sqweeze the body of the rivet ,that will either pull out the mandrel or at least pull it lower than the skin and you can easilly drill off the head .

  I hope it helps  ,at some point in time you will need to remove,repair,or replace a panel

and it easy to make some oblong holes on the process