Gareth, you make the assumption, as do many instructors and discussions on this subject, that the FO has a better understanding of the situation than the Captain.
The critical issue is why there should be an apparent difference in understanding of either the situation, or in deciding on a course of action. None of this presupposes that either pilot is right or wrong, just that there is a difference.
Thus every effort should be made to question individual understandings of the situation and then enquire of the Captain why there appears to be a difference in viewpoints – ‘I don’t understand, please explain; if we GA we might have to ...’. In this, the enquiry should try to provide additional or trigger information such as:-
the actual landing distance required for both wet and flooded runways,
if the runway has a lot of rubber deposits or is ungrooved,
the temp / wind profile, if it is conducive to windshear,
the missed approach routing,
Communication is essential in helping to resolve the differences in awareness; first for self-education and understanding, and second to aid the Captain by triggering a new assessment and explanation.
There is never a perfect match of understanding in any situation, the objective is to establish an acceptable shared mental model containing both the situation and proposed action.
If this is not resolvable, further communication should enquire a justification against the concerns – why is it safe to continue; only then might the communication be elevated; see PACE. However, remember it is important to avoid an antagonist confrontation and any thought of physical interaction; one consideration would be that intervention might have higher risks than continuing to land.
Problems like this are at the root of operational decision making –
‘Errors in Aviation Decision Making’
Also see
‘PACE’