aero2014

Hi all, I am accepted into the MIT Aero/Astro program for Masters, but I am wondering about the RA positions. I have asked my initial advisor and this professor said that there were some openings in his lab for next year and we will discuss it during either the Visit day or during a phone call. However, is it custom to also ask other professors about RA positions? I am afraid I will end up not getting an RA position and be left without funding and therefore want to spread my chances, but I also do not want to insult my initial advisor (when I ask other professors, he might think I do not like his lab). Could you guys give me some advice on the matter? Thanks!