I remember watching a documentary on a similar issue. The study was conducted on a temperature basis. It was thought that the girlfriend/wives of men who worked in hot environments (mines, steel factory etc) were more likely have boys. However, they found no convincing evidence.
Just had a look at the Oz bureau of stats. and a population chart shows that the age goups 0 to 10 that there are slightly more boys than girls.
A friend of mine has 19,000 hours and his wife was a commercial pilot. They have 2 boys!
U2