should be in the rules
I'm not one for over regulation but personally I think the CAA should include some verbiage in the conditions when they issue an airline it's licence. And the rules should say that when there is a schedule change then the airline has a duty to try and notify the passenger. Given email/sms etc then the cost nowadays is negligible if the capability is built into the reservation IT system.
It's the same as the trains in the the SouthEast being built without toilets, where are the regulators saying if you want a licence to operate there is a baseline you cannot go beneath when being fair with the consumer? That's why we have regulators!
G