Can a man eat on plane when traveling on chol hamoed Sukkos?
Yes, one who is travelling and due to his travels has no access to a Sukkah is exempt from this obligation and may eat out of the Sukka. Igros Moshe rules that one should refrain from going on a trip for no reason other than pleasure when it will cause this exemption. Most other authorities do not mention this concern.
See here for sources and extended discussion.