QSIT is the Quality Systems Inspection Technique. It is (my words) the way to 'get the most bang for the (inspection) buck'. It is a methodology of hitting the 'most important' elements of a medical device company's Quality System, and leveraging touch-points between system to (somwehat) thoroughly address the appropriate (for the company) elements of 21 CFR 820.
It will have to be revised (but not much, IMO) with any alignment between 21 CFR 820 and 13485, and there is a non-zero chance that it would simply be dropped if a coherent MDSAP-like approach.
Generally: There is no systemic distinction between "CA" and "PA". The FDA inspectors don't consider things like 'mistake proofing' or changing machine fluids to be PA... a PA takes place in a common formal process similar to CA, with the difference being CA are for non-conformances that have occurred. As a practical matter no medical device company would formally start PA for certain things that (for example) would just be risk controls in a FMEA. The necessary steps of a PA are essentially done, but the PA process requires whatever documentation/approvals it requires while a lot of things that could be considered PA will just be incorporated into some other process (equipment management, calibration, training, risk management, whatever) and never formally see the PA process.
I think the medical device industry would be well-served by formally getting rid of the PA terminology. I have observed that lumping PA with CA has had an unfortunate side effect whereby (some) companies will go out of their way to avoid formal PAs because of the documentation burden and the necessary critical thinking about 'effectiveness checks'. These companies don't necessarily skimp on things like maintaining equipment, its just that they see no value in formally documenting these sorts of internal decisions in more than one system... if they've made poor choices it will (possibly) eventually get handled through the CA process.
