Also put into context 'bald tyres ' , 747 classic AMM stated 'worn tyres are a maintenance issue not a safety issue' , very useful with FE's trying to get wheels changed down route !!! Both airlines under FAA , also station handling manual for A340 and 777 permitted rtb from outstation with worn tyres , from a large european carrier . Note this is for wear , not for damage which is a different , i.e safety issue. The point i'm making is some defects may appear to be kept until return to base , but is perfectly safe . I think the relevant question is where crews are put under pressure where they dont have a routine turn round done by engineering , i.e they're doing it themselves very commonly esp on shorthaul and charter. Any problem then requires a call to MCC , calling out a locally based engineer then is a cost , if available , so putting 'pressure ' on crews to carry on .