Probably just accomodating 21st-century practices. It is very rare for female actors to be called "actresses" these days (it's a pointless piece of implied sexism), and the term "aviatrix" itself implies that a pilot who is female is somehow "special" or "unusual". In the post-jurassic era such condescending drivel is no longer acceptable.
What on earth is condescending about it? Is it any more condescending than referring to a male pilot as an aviator?
After is, it's TCT that goes on about how significant her gender is, nobody else regards it as remotely relevant.