Banks and firms that uses their services are audited thoug. It is not blind trust. And regadress the tech used there would sitll be audits.

You dont need 51% attack to corrupt a ledger. Just enter incorrect info and the ledger is wrong. Not a damn thing a blockchain can do about that. Same issue is with any trustless system where you have to trust someone to input the correct info/do the agreed thing/ship the ordered physical item.

I have not seen any.

Thats not really true at leat according to aircrash investigation shows. Crew can make mistakes hours earlier that might lead to a crash or accident later. Mess up something during preflight checks and that can be the issue during later stage. Flights are long.