There was an article posted (I believe here) a while back about aerospace software development. They talked about the processes used to develop the software and it was definitely in line with engineering rigor. However, it went on to say the people doing the work were not professional engineers. So, at least in some countries, you still could not call it software engineering.
I'd guess that a professional engineer is still required to sign off on the software before a plane gets certification. The same happens when non-licensed-engineers work on other engineering projects. Perhaps the software part does have less engineers working on it percentage wise.
