J.E.
You could wait until you get back or you could start it at Grandmas house. You will be there 10 days that should be enough time for the baby to adjust and just think how nice it will be for Grandma to be there for one of the babys "firsts." That way you won't have to worry about it on the plane going and you will know what to expect on the way back home since it will be 10 days in already.
P.S. My kids did not have a problem either way when they started food. Good luck!