I think there is a fairly widespread misconception on this forum that there is one certifiable level of risk that can be defined as ALARP. The practicable part of the acronym allows for timely work.
If, for example a fault was found with fleet wide ramifications for any airliner you care to think of, the chances are the entire fleet of hundreds of aircraft would not be grounded, but given a suitable timescale to effect a modification. In the case of the RAF, faults which require immediate rectification will in effect ground the aircraft until rectified, whereas those deemed acceptable within a given timeframe will be given that time for rectification and afterwards would be grounded until the work was complete.
Continuing to operate with a level of risk that is understood and tolerated within banded limits, whilst working towards a higher standard is reasonable whilst remaining practicable.