Originally Posted by sdsearch

If they do say exactly that, it sounds like a spoken typo.

What would be correct is: "a member of the oneworld alliance."

Ie, the alliance is called oneworld, so it's correct to say "the oneworld alliance", which is shorthand for "the alliance called oneworld", but it is not correct to say "a member of oneworld Alliance", because that's shorthand for "a member of the organization called oneworld Alliance".

By the way, I'm writing it as oneworld because that's the way I see it painted on the sides of some planes (the "one" much "darker" type than the "world").