This is what I was told:
Making planes female has the same background as it has on ships.
Considering that the captain is the boss on board ( of a ship / plane) and the "thing" he "drives" is his wife it of course has to be female.
This is also the reason why a ship's captain would always go down with HIS ship if it sank, since they "belong together".
Today however the captain does no longer have to be male but because of the history of calling planes females it just stays that what way and for me as a male I rather look at a she then at a him while spotting.
However, the 747 has been considered male because of it's size in relation to the then common 707. After all it's a Jumbo and not a Jumborette.
[Edited 2003-09-09 14:54:56]