Who plays major role in the implementation of 360Degree PAs?

HR definetly plays a key role as the system can be tampered easily if not driven with the right intent. From a design perspective and from communication and culture expectation setting, HR will have to own the process.

HR with the colaboration of all the Department Heads and Supervisors.

Definately HR plays a vital role to implement the360 degree performance appraisal by formulating policies, formats, feedback and measure the employees effectiveness.

can say the HRD is the base to implement the360degree PAs. 

it is a collaborative role between HR department and different respective business units head