Re “Should a braking action have been offered or was it not offered as it was unmeasurable on the slippery bits?”
We must be careful with terms and definitions associated with this subject:
ICAO ‘braking action’ is a description, and ranges from ‘Good’ to ‘Poor’, the US in particular has differing terms; all of these are associated with a measured runway friction.
The UK appears to use ‘runway braking action’ as being the friction measurement.
UK AIP AD1.1.1 states:-
15.8 When a runway is contaminated by water (ie more than 3 mm), wet snow or slush, a braking action report will not be available due to the limitations of existing friction measuring equipment …
Thus, the reported circumstances suggest that the aerodrome operator has interpreted the conditions as ‘contaminated’ (friction not measured or not reportable).
However, in ICAO terms a descriptive braking action could be given if available.
I suggest that an aerodrome operator would be reluctant to do this without a friction measurement. Therefore, all that might be available is a PIREP, which if available, might not be very reliable for take off depending on the location of the de-icing fluid and the ‘slippery when wet’ sections of the runway – rubber deposits?.
Overall, this suggests that operators should use contaminated performance data.
This might be the conclusion from additional information provided by the aerodrome operator (and how is that determined?) …, but its always the aircraft operator’s responsibility – the pilot’s responsibility!