The Star Diaries and Memoirs of a Space Traveller by Stanislaw Lem. Think Gulliver Travels in space. Also, Tales of Prix the Pilot, from the same author. Amazingly deep, exciting and humorous at the same time. Invincible (also Lem's) might be a good idea if you like mystery with a fair bit of philosophy, but not everybody would find it suitable for a plane trip.
Stanislaw Lem in general is a very good author (one of the few benefits of being a Pole is getting to read his books in original without needing to learn notoriously difficult Polish as a second language), but many of his works might not be suitable for a plane trip. His Master's Voice, for example, is a seemingly dinky book that actually has more "content" than some doorstopper series. Very interesting and satisfying to read, but also very difficult. Same deal with Solaris, though not to this extent.