Hi and welcome to the Chiari forum.
I have not required a second surgery and mine was in '09....and it could be what type of decompression surgery you had....did they open the dura, did they patch it, if so what type of patch?
Were ALL related conditions ruled out prior to your surgery?
You said you were flying until recently....how soon after surgery did you fly and how often?
I am aware of some that have had more than one surgery....reasons some had a second surgery were CSF leaks or a pseudomeningocele. Everyone's issues and need for a second surgery will be different.I know a few members that had a second surgery because the plate used over the dura came loose....and they had to fix the plate. Not everyone had a mesh plate installed so gain this is not going to help you with your issue to if you may need another surgery....
Look to see if you have any related condition and if they may be your issue, and also check to see if you have scar tissue that formed , as that can also cause a CSF obstruction and cause pain.
I hope this is somewhat helpful...do let us know how you are doing.