Here is just a thought:
A double rad alt failure will send the bus straight from normal to direct law when the gear is selected down and the autopilot is disconnected.Approach mode is not available.It helps to fly the approach in manual thrust as well in this case.
The workload can get very busy if you are manoeuvring on base leg,trying to get the FD to capture( because it will not in this case,and you haven't twigged why) and you ask for the gear down - and go straight into direct law and the autopilot disconnects!