How common is it to switch to a tenure-track position from a non-tenure-track position in the same institution? I am looking for answers from the perspective of U.S. institutions.  At some institutions (e.g., mine), a faculty member is allowed to switch tracks at the institution once in their career at that institution.  For example, a person who was hired as a non-tenure track research assistant professor can petition or apply to be a tenure-track assistant professor.  The process is a bit vague, but it happened to someone at my institution recently, which got me thinking about the question.  

The person--let's call him Dr. X--started out as a research assistant professor in Department Y on Well-Funded Project Z.  Due to administrative...restructuring, which dissolved Department Y, all of the professors in Department Y had to choose a new department in the School, and all of the professors working on Well-Funded Project Z ended up moving to Department A.  

I am curious whether this is a common occurrence.  I was casually talking to another, more senior professor (who also involved in Well-Funded Project Z), when it was revealed to me that our institution allows professors to change tracks once in their career.  I was wondering if others had seen something similar at their institutions, and related to that, is it ever a good idea to ask when interviewing for a non-tenure-track position whether there is a possibility of switching to a tenure-track position down the road or what the institution's policy is surrounding switching tracks?
Like many things in academia, the answer will likely depend upon the institution.  In most, I would think that a non-tenure-track and a tenure-track position are actually different positions.  You aren't just changing a title, but you are leaving one job and starting another (at the same institution). I would imagine that most do not have official rules about the number of times you can change jobs, although there may be unofficial scuttlebutt to the contrary.  This should be outlined in the faculty handbook/guide.


  Is it ever a good idea to ask when interviewing for a non-tenure-track position whether there is a possibility of switching to a tenure-track position down the road or what the institution's policy is surrounding switching tracks?


If you are interested in a tenure-track position, I think this is a very important question to be asking, and is not viewed negatively by any reasonable person. The chair or hiring committee should be able to let you know about this possibility.