ATSB's 1st Interim Report on the QF32 pitch-down accident describes the role division between the PRIMs:
Review of PRIM monitoring functions
The aircraft’s flight control system included three flight control primary computers (FCPCs, commonly known as PRIMs) and two flight control secondary computers (FCSCs, commonly known as SECs). One PRIM functioned as the master while the other two PRIMs could take over as master if a fault in the current master was detected. The master PRIM processed and sent control surface deflection orders to other computers, which executed them using servo-controls. The two other PRIMs continuously computed control orders and monitored control surface deflections but those orders were not actioned.
Each PRIM consisted of two independent parts, a Command (COM) part and a Monitor (MON) part. The MON part monitored the performance of the COM part and the position of the control surfaces. If there was a discrepancy between COM and MON, then the PRIM would ‘fault’ itself. The fault could be for only a part of the PRIM (for example, pitch channel) or for the whole PRIM. A PRIM could not generate a fault for the whole PRIM unless it was the master. The PRIM Fault parameter recorded by the FDR was active only for a fault of the whole PRIM and not for a partial fault (for example, a pitch channel fault). However, partial faults were recorded by the PFR.
For elevator control, the active servo-controller in normal operation was PRIM 1. The servo-controller priority order was PRIM 1, PRIM 2, SEC 1 and SEC2. If PRIM 1 could not perform this function, then the servo-control function reverted to PRIM 2 and so on.
Table 4 provides a sequence of events for the PRIMs and is based on a review of the FDR and PFR data by the aircraft manufacturer and investigation team.
Table 4: PRIM sequence of events
(table deleted, does not reproduce in PPRuNe - HN39)
In summary, the PRIM PITCH FAULTs and PRIM 3 FAULTs that occurred during the flight were consistent with the system design. They were consequences of the pitch-down events and not the initiators of those events.