"to be fully able" is correct and usable in written English.
You can use it when talking about someone's ability to do something completely or successfully. Example sentence: Sarah attended the training program in order to be fully able to handle the responsibilities of her new job.
Although it seemed to become a real capital again, it needed endless overambitious projects, for instance an airport such as Berlin-Brandenburg, to be fully able to compete with Germany's financial capital, Frankfurt.
It was the only way to be fully able to think about what I wanted to do with the rest of my life.
It strongly appears that humans' brains have yet to evolve enough to be fully able to deal with today's very different world of data and information about everybody and everything.
If you have too many personal issues of your own to sort out, you may not be fully able to help your friend.
The lay public might find your case superficially appealing, but they may not be fully able to judge the merits of all your technical evidence.
If you feel you might not be fully able to do so, stop listening.
Only two papers were judged to be of sufficient quality to have been fully able to include in explanatory meta-analyses (with appropriate sensitivity analyses for blinding) if differing outcomes had not prevented these from occurring (Table 2).
I'm not going to go back until I'm fully able to do it properly.
Consumer demand continues unabated and we need to ensure that UK SMEs are fully able to capitalise on this.
However, this latest draft does not go far enough to ensure persons with disabilities are fully able to benefit from Bank projects.
Śāntarakṣita considers that he is fully able to respond to the criticisms of Kumārila with his presentation of exclusions.
