I was wondering if this preposition can be used in the following ways
1) I've been working with ABC (a company) since 1990.
2) I'm flying with Cathay this time.
Aside from with, are there any other ways you would normally say where you're working at and which airline you're flying?
#2 is the most common way of saying which airline you've chosen, although we do also say "I'm flying/going on Cathay this time".
In #1, "with" does give some ambiguity though. If you are actually employed (as an official employee) then I would use "I've been working for ABC ..." or "I've been working at ABC ...". If you're a freelance worker, or self-employed in some other way, and ABC company are currently utilising your services, then "I've been working with ABC ..." would be fine.