Actions of maintenance personnel.
Factor list item no.39, 'Maintenance personnel de-activate rat probe heating'.
This is NOT exactly what they did,and is crucial to the causality and mindset leading to the accident.
They seem to have switched off a power supply ONE of the functions of which was to supply the rat probe heating.
They appear to have failed to consider the effect of loss of power to the other systems powered by the same supply,or considered that the lack of power to these systems did not constitute a MEL .infringement.
It is vital in a maintenance regime to consider the effects and consequences on other systems of ANY action taken,and to be sufficiently conversant with the whole system to properly analyse the effects overall.
I write this after 50+ years in designing and maintaining industrial control and safety systems,and I still approach any 'link it out/switch it off for now' fault solutions with great fear and trepidation and endless what else will it affect mind searching.