all the company can legally say is that he/she 'worked here' with no indication of ability
Don't know about airlines, but in my industry (IT/tech) if all you say is "I can confirm that XXX was employed by us from ... to..." then that can and will be glossed as "don't touch this person with a 1000 metre pole". If you would actually re-hire the person then you say all sorts of nice glowing things. You never say anything explicitly negative.