User manuals are indeed copyrighted. On the other hand, since the people building the cranes are most likely interested in people reading these manuals, there is a good chance that you would get permission to copy them, for example as part of a mobile app, if you ask the manufacturer.
On the other hand, it is possible that the manual was written by a third party, who receives some fixed amount of money for every manual that the manufacturer gives away to customers for free. In that case, copying would destroy that persons earnings, so permission would be unlikely.
You definitely need to ask for permission and can't go forward without permission. It would also be possible that the crane manufacturer will want to check out your app to make sure that everything is correct - if someone damages a crane because of some omissions in your app, that would be very bad for them.